Oracle® TimesTen In-Memory Database

Replication Guide

11g Release 2 (11.2.2)

E21635-11

October 2014

Oracle TimesTen In-Memory Database Replication Guide, 11g Release 2 (11.2.2)

E21635-11

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Contents

Preface

- Audience

- Related documents

- Conventions

- Documentation Accessibility

What's New

- New features in Release 11.2.2.8.0

- New features in Release 11.2.2.7.0

- New features in Release 11.2.2.5.0

- New features in Release 11.2.2.4.0

- New features in Release 11.2.2.2.0

- New features in Release 11.2.2.1.0

- New features in Release 11.2.2.0.0

1 Overview of TimesTen Replication

- What is replication?

- Requirements for replication compatibility

- Replication agents

- Copying updates between databases

- Default replication

- Return receipt replication

- Return twosafe replication

- Types of replication schemes

- Active standby pair with read-only subscribers

- Classic replication

- Full database replication or selective replication

- Unidirectional or bidirectional replication

- Direct replication or propagation

- Cache groups and replication

- Replicating an AWT cache group

- Replicating an AWT cache group with a subscriber propagating to an Oracle database

- Replicating a read-only cache group

- Sequences and replication

- Foreign keys and replication

- Aging and replication

2 Getting Started

- Configuring an active standby pair with one subscriber

- Step 1: Create the DSNs for the master and the subscriber databases

- Step 2: Create a table in one of the master databases

- Step 3: Define the active standby pair

- Step 4: Start the replication agent on a master database

- Step 5: Set the state of a master database to 'ACTIVE'

- Step 6. Create a user on the active database

- Step 7: Duplicate the active database to the standby database

- Step 8: Start the replication agent on the standby database

- Step 9. Duplicate the standby database to the subscriber

- Step 10: Start the replication agent on the subscriber

- Step 11: Insert data into the table on the active database

- Step 12: Drop the active standby pair and the table

- Configuring a replication scheme with one master and one subscriber

- Step 1: Create the DSNs for the master and the subscriber

- Step 2: Create a table and replication scheme on the master database

- Step 3: Create a table and replication scheme on the subscriber database

- Step 4: Start the replication agent on each database

- Step 5: Insert data into the table on the master database

- Step 6: Drop the replication scheme and table

3 Defining an Active Standby Pair Replication Scheme

- Overview of master database states

- Duplicating a database

- Restrictions on active standby pairs

- Defining the DSNs for the databases

- Table requirements for active standby pairs

- Defining an active standby pair replication scheme

- Identifying the databases in the active standby pair

- Using a return service for an active standby pair

- Setting STORE attributes for an active standby pair

- Configuring network operations for an active standby pair

- Using automatic client failover for an active standby pair

- Including or excluding database objects from replication

- Replicating tables with foreign key relationships in an active standby pair

- Materialized views in an active standby pair

- Replicating sequences in an active standby pair

4 Defining Attributes and Options for a Replication Scheme

- Using a return service

- Specifying a different return service for each subscriber in a classic replication scheme

- RETURN RECEIPT

- RETURN RECEIPT BY REQUEST

- RETURN TWOSAFE

- RETURN TWOSAFE BY REQUEST

- NO RETURN

- Setting STORE attributes

- Setting the return service timeout period

- Managing return service timeout errors and replication state changes

- Column definition options for replicated tables

- Examples for an active standby pair replicating tables with table definition checking set to relaxed

- Examples for classic replication scheme with table definition checking set to relaxed

- Compressing replicated traffic

- Port assignments

- Setting wait timeout for response from remote replication agents

- Setting the transaction log failure threshold

- Suspending or resuming classic replication in response to conflicts

- Configuring the network

- Network bandwidth requirements

- Replication in a WAN environment

- Configuring network interfaces with the ROUTE clause

- Configuring network interfaces when not using the ROUTE clause

- Identifying database hosts on UNIX without using the ROUTE clause

- Host name resolution on Windows

- User-specified addresses for TimesTen daemons and subdaemons

- Identifying the local host of a replicated database

5 Administering an Active Standby Pair without Cache Groups

- Setting up an active standby pair with no cache groups

- Recovering from a failure of the active database

- Recovering when the standby database is ready

- When replication is return receipt or asynchronous

- When replication is return twosafe

- Failing back to the original nodes

- Recovering from a failure of the standby database

- Recovering after a dual failure of both active and standby databases

- Recover the active database

- Recover the standby database

- Recovering from the failure of a subscriber database

- Reversing the roles of the active and standby databases

- Detection of dual active databases

6 Administering an Active Standby Pair with Cache Groups

- Active standby pairs with cache groups

- Setting up an active standby pair with a read-only cache group

- Setting up an active standby pair with an AWT cache group

- Changing user names or passwords used by replication

- Recovering from a failure of the active database

- Recovering when the standby database is ready

- When replication is return receipt or asynchronous

- When replication is return twosafe

- When there is unsynchronized data in the cache groups

- Failing back to the original nodes

- Recovering from a failure of the standby database

- Recovering after a dual failure of both active and standby databases

- Recover the active database and duplicate a new standby database

- Recover the standby database to be the new active master

- Restore the active master from a backup

- Recovering from the failure of a subscriber database

- Reversing the roles of the active and standby databases

- Detecting dual active databases

- Using a disaster recovery subscriber in an active standby pair

- Requirements for using a disaster recovery subscriber with an active standby pair

- Rolling out a disaster recovery subscriber

- Switching over to the disaster recovery site

- Creating a new active standby pair after switching to the disaster recovery site

- Switching over to a single database

- Returning to the original configuration at the primary site

7 Altering an Active Standby Pair

- Making DDL changes in an active standby pair

- Controlling replication of objects to all databases in an active standby pair

- DDL statements that can be automatically replicated

- Creating a new PL/SQL object in an existing active standby pair

- Restrictions on making DDL changes in an active standby pair

- Examples: Making DDL changes in an active standby pair

- Making other changes to an active standby pair

- Examples: Altering an active standby pair

8 Using Oracle Clusterware to Manage Active Standby Pairs

- Overview of how Oracle Clusterware can manage TimesTen

- Required privileges

- Hardware and software requirements

- Restricted commands and SQL statements

- Configuring Oracle Clusterware management with the cluster.oracle.ini file

- Configuring basic availability

- Configuring advanced availability

- Including cache groups in the active standby pair

- Including the active standby pair in a cache grid

- Implementing application failover

- Recovering from permanent failure of both master nodes

- Using the RepDDL attribute

- Creating and initializing a cluster

- Install Oracle Clusterware

- Install TimesTen on each host

- Register the TimesTen cluster information

- Start the TimesTen cluster agent

- Create and populate a TimesTen database on one host

- Create system DSN files on other hosts

- Create a cluster.oracle.ini file

- Create the Oracle Clusterware resources to manage virtual IP addresses

- Create an active standby pair replication scheme

- Start the active standby pair and the applications

- Load cache groups

- Include more than one active standby pair in a cluster

- Configure an Oracle database as a disaster recovery subscriber

- Configure a read-only subscriber that is not managed by Oracle Clusterware

- Using Oracle Clusterware with a TimesTen cache grid

- Creating and initializing a cluster of cache grid members

- Failure and recovery for active standby pair grid members

- Making schema changes to active standby pairs in a grid

- Add a cache group

- Drop a cache group

- Change an existing cache group

- Recovering from failures

- How TimesTen performs recovery when Oracle Clusterware is configured

- When an active database or its host fails

- When a standby database or its host fails

- When read-only subscribers or their hosts fail

- When failures occur on both master nodes

- Automatic recovery when not attached to a grid

- Manual recovery of both nodes of an active standby pair grid member

- Manual recovery for advanced availability

- Manual recovery for basic availability

- Manual recovery to the same master nodes when databases are corrupt

- Manual recovery when RETURN TWOSAFE is configured

- When more than two master hosts fail

- Perform a forced switchover after failure of the active database or host

- Clusterware management

- Performing a rolling upgrade of Oracle Clusterware software

- Upgrading TimesTen

- Managing hosts in the cluster

- Adding a host to the cluster

- Removing a host from the cluster

- Managing active standby pairs in a cluster

- Adding an active standby pair to a cluster

- Removing an active standby pair from a cluster

- Managing read-only subscribers in the active standby pair

- Adding a read-only subscriber managed by Oracle Clusterware

- Removing a read-only subscriber managed by Oracle Clusterware

- Adding or dropping a read-only subscriber not managed by Oracle Clusterware

- Rebuilding a read-only subscriber not managed by Oracle Clusterware

- Changing the schema

- Facilitating schema change for Oracle Clusterware

- Managing subscribers and database attributes

- Reversing the roles of the master databases

- Moving a database to a different host

- Performing host or network maintenance

- Performing maintenance on the entire cluster

- Changing user names or passwords when using Oracle Clusterware

- Managing the TimesTen database RAM policy

- Monitoring cluster status

- Obtaining cluster status

- Message log files

9 Defining Classic Replication Schemes

- Designing a highly available system

- Considering failover and recovery scenarios

- Making decisions about performance and recovery tradeoffs

- Distributing workloads

- Defining a classic replication scheme

- Owner of the replication scheme and replicated objects

- Database names

- Table requirements and restrictions for classic replication schemes

- Restrictions for classic replication schemes involving multiple masters

- Defining replication elements

- Defining the DATASTORE element

- Defining table elements

- Replicating tables with foreign key relationships in a classic replication scheme

- Replicating sequences

- Views and materialized views in a replicated database

- Checking for replication conflicts on table elements

- Setting transmit durability on DATASTORE element

- Using a return service in a classic replication scheme

- Setting STORE attributes in a classic replication scheme

- Configuring network operations for a classic replication scheme

- Classic replication scheme syntax examples

- Single classic subscriber schemes

- Multiple subscriber classic replication schemes with return services and a log failure threshold

- Replicating tables to different subscribers

- Propagation scheme

- Bidirectional split workload schemes

- Bidirectional distributed workload scheme

- Applying a classic replication scheme to a database

- Creating classic replication schemes with scripts

10 Altering a Classic Replication Scheme

- Altering a classic replication scheme

- Adding a table or sequence to an existing classic replication scheme

- Adding a PL/SQL object to an existing classic replication scheme

- Adding a DATASTORE element to an existing classic replication scheme

- Including tables or sequences when you add a DATASTORE element

- Excluding a table or sequence when you add a DATASTORE element

- Dropping a table or sequence from a classic replication scheme

- Dropping a table or sequence that is replicated as part of a DATASTORE element

- Dropping a table or sequence that is replicated as a TABLE or SEQUENCE element

- Creating and adding a subscriber database to a classic replication scheme

- Dropping a subscriber database from a classic replication scheme

- Changing a TABLE or SEQUENCE element name in a classic replication scheme

- Replacing a master database in a classic replication scheme

- Eliminating conflict detection in a classic replication scheme

- Eliminating the return receipt service in a classic replication scheme

- Changing the port number for a classic replication scheme

- Changing the replication route

- Changing the log failure threshold

- Altering a replicated table in a classic replication scheme

- Truncating a replicated table in a classic replication scheme

- Dropping a classic replication scheme

11 Setting Up a Replicated System

- Setting up the replication environment

- Establishing the databases

- Connection attributes for replicated databases

- Configuring parallel replication

- Configuring automatic parallel replication

- Configuring automatic parallel replication with disabled commit dependencies

- Configuring user-defined parallel replication for classic replication schemes

- Managing the transaction log on a replicated database

- About log buffer flushing

- About transaction log growth on a master database

- Setting connection attributes for logging

- Duplicating a master database to a subscriber

- Configuring a large number of subscribers

- Replicating databases across releases

- Starting and stopping the replication agents

- Setting the replication state of subscribers

12 Monitoring Replication

- Show state of replication agents

- Using ttStatus to obtain replication agent status

- Using ttAdmin -query to confirm policy settings

- Using ttDataStoreStatus to obtain replication agent status

- Show master database information

- Using ttRepAdmin to display information about the master database

- Querying replication tables to obtain information about a master database

- Show subscriber database information

- Display subscriber status with the ttRepAdmin utility

- Display subscriber status with the ttReplicationStatus built-in procedure

- Display information about subscribers through querying replication tables

- Subscriber information

- Show the configuration of replicated databases

- Display configuration information with the ttIsql repschemes command

- Display configuration information with the ttRepAdmin utility

- Display configuration information through querying replication tables

- Show replicated log records

- Monitor replication with the TTREP.REPPEERS table

- Monitor replication with the ttLogHolds built-in procedure

- Monitor replication with the ttRepAdmin utility

- Monitor replication with the ttBookMark built-in procedure

- Use ttRepAdmin to show replication status

- MAIN thread status fields

- Replication peer status fields

- TRANSMITTER thread status fields

- RECEIVER thread status fields

- Check the status of return service transactions

- Determine if return service is disabled

- Check last returned status for a return service

- Analyze outstanding transactions in the replication log

13 Resolving Replication Conflicts

- How replication conflicts occur

- Update and insert conflicts

- Delete/update conflicts

- Using a timestamp to resolve conflicts

- Timestamp comparisons for local updates

- Configuring timestamp comparison

- Including a timestamp column in replicated tables

- Configuring the CHECK CONFLICTS clause

- Enabling system timestamp column maintenance

- Enabling user timestamp column maintenance

- Reporting conflicts

- Reporting conflicts to a text file

- Reporting conflicts to an XML file

- Reporting uniqueness conflicts

- Reporting update conflicts

- Reporting delete/update conflicts

- Suspending and resuming the reporting of conflicts

- The conflict report XML Document Type Definition

- The main body of the document

- The uniqueness conflict element

- The update conflict element

- The delete/update conflict element

14 Improving Replication Performance

- Adjust transaction log buffer size and CPU

- Performance considerations when altering tables that are replicated

- Increase replication throughput for active standby pairs

- Limit replication transmitters, receivers, and XLA readers

15 Managing Database Failover and Recovery

- Overview of database failover and recovery

- General failover and recovery procedures

- Subscriber failures

- Master failures

- Automatic catch-up of a failed master database

- When master catch-up is required for an active standby pair

- Failures in bidirectional distributed workload schemes

- Network failures

- Failures involving sequences

- Recovering a failed database

- Recovering a failed database from the command line

- Recovering a failed database from a C program

- Recovering nondurable databases

- Writing a failure recovery script

A TimesTen Configuration Attributes for Oracle Clusterware

- List of attributes

- Required attributes

- MasterHosts

- Conditionally required attributes

- AppCheckCmd

- AppFailureInterval

- AppName

- AppRestartAttempts

- AppStartCmd

- AppStopCmd

- AppType

- AppUptimeThreshold

- CacheConnect

- GridPort

- MasterVIP

- RemoteSubscriberHosts

- RepBackupDir

- SubscriberHosts

- SubscriberVIP

- VIPInterface

- VIPNetMask

- Optional attributes

- AppFailoverDelay

- AppFailureThreshold

- AppScriptTimeout

- AutoRecover

- DatabaseFailoverDelay

- FailureThreshold

- MasterStoreAttribute

- RepBackupPeriod

- RepDDL

- RepFullBackupCycle

- ReturnServiceAttribute

- SubscriberStoreAttribute

- TimesTenScriptTimeout

Index

Preface

Oracle TimesTen In-Memory Database (TimesTen) is a relational database that is memory-optimized for fast response and throughput. The database resides entirely in memory at runtime and is persisted to disk storage for the ability to recover and restart. Replication features enable high availability. TimesTen supports standard application interfaces JDBC, ODBC, and ODP.NET, in addition to Oracle interfaces PL/SQL, OCI, and Pro*C/C++. TimesTen is available separately or as a cache for Oracle Database.

High availability for the in-memory database is provided through real-time transactional replication. This book covers how to configure, manage, and use replication.

Audience

This document is intended for application developers and system administrators who use and administer TimesTen to TimesTen Replication.To work with this guide, you should understand how database systems work. You should also have knowledge of SQL (Structured Query Language) and either ODBC (Open DataBase Connectivity) or JDBC (JavaDataBase Connectivity).

Related documents

TimesTen documentation is available on the product distribution media and on the Oracle Technology Network:

http://www.oracle.com/technetwork/database/database-technologies/timesten/documentation/index.html

Oracle Database documentation is also available on the Oracle Technology network. This may be especially useful for Oracle Database features that TimesTen supports, but does not document.

http://www.oracle.com/pls/db112/homepage/

Conventions

TimesTen supports multiple platforms. Unless otherwise indicated, the information in this guide applies to all supported platforms. The term Windows refers to all supported Windows platforms. The term UNIX applies to all supported UNIX and Linux platforms. See "Platforms" in Oracle TimesTen In-Memory Database Release Notes for specific platform versions supported by TimesTen.

Note:
In TimesTen documentation, the terms "data store" and "database" are equivalent. Both terms refer to the TimesTen database.

This document uses the following text conventions:

Convention

Meaning

boldface

Boldface type indicates graphical user interface elements associated with an action, or terms defined in text or the glossary.

italic

Italic type indicates book titles, emphasis, or placeholder variables for which you supply particular values.

monospace

Monospace type indicates commands within a paragraph, URLs, code in examples, text that appears on the screen, or text that you enter.

italic monospace

Italic monospace type indicates a variable in a code example that you must replace. For example:
Driver=install_dir/lib/libtten.sl

Replace install_dir with the path of your TimesTen installation directory.

[ ]

Square brackets indicate that an item in a command line is optional.

{ }

Curly braces indicated that you must choose one of the items separated by a vertical bar ( | ) in a command line.

|

A vertical bar (or pipe) separates alternative arguments.

. . .

An ellipsis (. . .) after an argument indicates that you may use more than one argument on a single command line.

%

The percent sign indicates the UNIX shell prompt.

#

The number (or pound) sign indicates the UNIX root prompt.

TimesTen documentation uses these variables to identify path, file and user names:

Convention

Meaning

install_dir

The path that represents the directory where the current release of TimesTen is installed.

TTinstance

The instance name for your specific installation of TimesTen. Each installation of TimesTen must be identified at install time with a unique alphanumeric instance name. This name appears in the install path.

bits or bb

Two digits, either 32 or 64, that represent either the 32-bit or 64-bit operating system.

release or rr

The first three parts in a release number, with or without dots. The first three parts of a release number represent a major TimesTen release. For example, 1122 or 11.2.2 represents TimesTen 11g Release 2 (11.2.2).

jdk_version

Two digits that represent the version number of the major JDK release. Specifically, 14 represent JDK 1.4; 5 represents JDK 5.

DSN

The data source name.

Documentation Accessibility

For information about Oracle's commitment to accessibility, visit the Oracle Accessibility Program website at http://www.oracle.com/pls/topic/lookup?ctx=acc&id=docacc.

Access to Oracle Support

Oracle customers have access to electronic support through My Oracle Support. For information, visit http://www.oracle.com/pls/topic/lookup?ctx=acc&id=info or visit http://www.oracle.com/pls/topic/lookup?ctx=acc&id=trs if you are hearing impaired.

What's New

This preface summarizes the new features of Oracle TimesTen In-Memory Database release 11.2.2 that are documented in this guide. It provides links to more information.

New features in Release 11.2.2.8.0

- You can disable commit dependencies for automatic parallel replication for an active standby pair that uses asynchronous replication and does not contain cache groups. This provides parallel replication over multiple threads that automatically enforces transactional dependencies, but does not enforce transactions to be committed in the same order on the subscriber database as on the master database. For more information, see "Configuring automatic parallel replication with disabled commit dependencies."

New features in Release 11.2.2.7.0

- The DDLReplicationLevel and DDLReplicationAction connection attributes control what objects that are created or dropped by DDL statements are automatically replicated to the databases involved in an active standby pair replication scheme. For this release, a new level of 3 (not the default) for the DDLReplicationLevel connection attribute adds replication of the CREATE VIEW or DROP VIEW statements, the CREATE SEQUENCE or DROP SEQUENCE statements, and the result of running the ttCacheUidPwdSet built-in procedure to set the cache administration user name and password. When DDLReplicationLevel=3 and the DDLReplicationAction connection attribute is set to INCLUDE, then any new sequences created are included in the replication scheme. See "Controlling replication of objects to all databases in an active standby pair" for details.

- When using Oracle Clusterware, you must execute the new ttCWAdmin -reauthenticate command after modifying any user name or password to enable Oracle Clusterware to store these new user names and passwords. For full details, see "Changing user names or passwords when using Oracle Clusterware".

New features in Release 11.2.2.5.0

- When you use ALTER TABLE to add or drop columns, extraneous space or partitions could be added, which can hinder the performance of replication. If you are using relaxed replication, you can eliminate the extraneous space and partitions with ttMigrate -relaxedUpgrade. For details, see "Column definition options for replicated tables".

- There is a new command, the -logAnalyze command, in the ttXactLog utility that analyzes the replication logs to measure how much is left to replicate from the active to a standby master and any subscribers and if the current configuration distributes the load appropriately for parallel replication. For more details, see "Analyze outstanding transactions in the replication log".

New features in Release 11.2.2.4.0

- You can now specify an alias or the IP address of the network interface when you want to use a specific local or remote network interface over which database duplication occurs. For details, see "Duplicating a database".

New features in Release 11.2.2.2.0

- By default, replication is performed with a single thread. You can increase your performance by configuring parallel replication, which configures multiple threads for sending updates from the source database to the target database and for applying the updates on the target database. For more information, see "Configuring parallel replication".

New features in Release 11.2.2.1.0

- You have additional control over TimesTen application behavior when Oracle Clusterware is managing a TimesTen active standby pair. The AppFailureInterval, AppRestartAttempts, and AppUptimeThreshold Clusterware attributes are new. See "Implementing application failover".

New features in Release 11.2.2.0.0

- Durable commit behavior has changed. See "DURABLE COMMIT".

- LOB columns can be replicated. See "Table requirements for active standby pairs" and "Table requirements and restrictions for classic replication schemes".

- TimesTen provides in-memory columnar compression. However, you cannot replicate tables with compressed columns. This restriction is mentioned in "Table requirements for active standby pairs" and "Table requirements and restrictions for classic replication schemes".

1 Overview of TimesTen Replication

The following sections provide an overview of TimesTen replication:

- What is replication?

- Requirements for replication compatibility

- Replication agents

- Copying updates between databases

- Types of replication schemes

- Cache groups and replication

- Sequences and replication

- Foreign keys and replication

- Aging and replication

What is replication?

Replication is the process of maintaining copies of data in multiple databases. The purpose of replication is to make data highly available to applications with minimal performance impact. In addition to providing recovery from failures, replication schemes can also distribute application workloads across multiple databases for maximum performance and facilitate online upgrades and maintenance.

Replication is the process of copying data from a master database to a subscriber database. Replication is controlled by replication agents for each database. The replication agent on the master database reads the records from the transaction log for the master database. It forwards changes to replicated elements to the replication agent on the subscriber database. The replication agent on the subscriber database then applies the updates to its database. If the subscriber replication agent is not running when the updates are forwarded by the master, the master retains the updates in its transaction log until they can be applied at the subscriber database.

TimesTen recommends the active standby pair configuration for highest availability. In an active standby pair replication scheme, the data is copied from the active database to the standby database before being copied to read-only subscribers.

An entity that is replicated with all of its contents between databases is called a replication element. TimesTen supports databases, cache groups, tables and sequences as replication elements. TimesTen also replicates XLA bookmarks. An active standby pair is the only supported replication scheme for databases with cache groups.

In addition, when you execute certain DDL statements in an active standby pair, some statements are replicated against the other nodes in the replication scheme. For more details, see "Making DDL changes in an active standby pair".

Requirements for replication compatibility

TimesTen replication is supported only between identical platforms and bit-levels. Although you can replicate between databases that reside on the same host, replication is generally used for copying updates into a database that resides on another host. This helps prevent data loss from host failure.

The databases must have DSNs with identical DatabaseCharacterSet and TypeMode database attributes.

Replication agents

Replication between databases is controlled by a replication agent. Each database is identified by:

- A database name derived from the file system's path name for the database

- A host name

The replication agent on the master database reads the records from the transaction log and forwards any detected changes to replicated elements to the replication agent on the subscriber database. The replication agent on the subscriber database then applies the updates to its database. If the subscriber agent is not running when the updates are forwarded by the master, the master retains the updates in the transaction log until they can be transmitted.

The replication agents communicate through TCP/IP stream sockets. The replication agents obtain the TCP/IP address, host name, and other configuration information from the replication tables described in Oracle TimesTen In-Memory Database System Tables and Views Reference.

Copying updates between databases

By default, updates are copied between databases asynchronously. While asynchronous replication provides the best performance, it does not provide the application with confirmation that the replicated updates were committed on subscriber databases. For applications that need higher levels of confidence that the replicated data is consistent between the master and subscriber databases, you can enable either return receipt or return twosafe service.

- The return receipt service loosely synchronizes the application with the replication mechanism by blocking the application until replication confirms that the update has been received by the subscriber.

- The return twosafe service provides a fully synchronous option by blocking the application until replication confirms that the update has been both received and committed on the subscriber.

Return receipt replication impacts performance less than return twosafe, but at the expense of less synchronization. The operational details for asynchronous, return receipt, and return twosafe replication are discussed in these sections:

- Default replication

- Return receipt replication

- Return twosafe replication

Default replication

When using default TimesTen replication, an application updates a master database and continues working without waiting for the updates to be received and applied by the subscribers. The master and subscriber databases have internal mechanisms to confirm that the updates have been successfully received and committed by the subscriber. These mechanisms ensure that updates are applied at a subscriber only once, but they are completely independent of the application.

Default TimesTen replication provides maximum performance, but the application is completely decoupled from the receipt process of the replicated elements on the subscriber.

Figure 1-1 Basic asynchronous replication cycle

The default TimesTen replication cycle is:

1. The application commits a local transaction to the master database and is free to continue with other transactions.

2. During the commit, the TimesTen daemon writes the transaction update records to the transaction log buffer.

3. The replication agent on the master database directs the daemon to flush a batch of update records for the committed transactions from the log buffer to a transaction log file. This step ensures that, if the master fails and you need to recover the database from the checkpoint and transaction log files, the recovered master contains all the data it replicated to the subscriber.

4. The master replication agent forwards the batch of transaction update records to the subscriber replication agent, which applies them to the subscriber database. Update records are flushed to disk and forwarded to the subscriber in batches of 256K or less, depending on the master database's transaction load. A batch is created when there is no more log data in the transaction log buffer or when the current batch is roughly 256K bytes.

5. The subscriber replication agent sends an acknowledgement back to the master replication agent that the batch of update records was received. The acknowledgement includes information on which batch of records the subscriber last flushed to disk. The master replication agent is now free to purge from the transaction log the update records that have been received, applied, and flushed to disk by all subscribers and to forward another batch of update records, while the subscriber replication agent asynchronously continues on to Step 6.

6. The replication agent at the subscriber updates the database and directs the daemon to write the transaction update records to the transaction log buffer.

7. The replication agent at the subscriber database uses a separate thread to direct the daemon to flush the update records to a transaction log file.

Return receipt replication

The return receipt service provides a level of synchronization between the master and a subscriber database by blocking the application after commit on the master until the updates of the committed transaction have been received by the subscriber.

An application requesting return receipt updates the master database in the same manner as in the basic asynchronous case. However, when the application commits a transaction that updates a replicated element, the master database blocks the application until it receives confirmation that the updates for the completed transaction have been received by the subscriber.

Return receipt replication trades some performance in order to provide applications with the ability to ensure higher levels of data integrity and consistency between the master and subscriber databases. In the event of a master failure, the application has a high degree of confidence that a transaction committed at the master persists in the subscribing database.

Figure 1-2 Return receipt replication

Figure 1-2 shows that the return receipt replication cycle is the same as shown for the basic asynchronous cycle in Figure 1-1, only the master replication agent blocks the application thread after it commits a transaction (Step 1) and retains control of the thread until the subscriber acknowledges receipt of the update batch (Step 5). Upon receiving the return receipt acknowledgement from the subscriber, the master replication agent returns control of the thread to the application (Step 6), freeing it to continue executing transactions.

If the subscriber is unable to acknowledge receipt of the transaction within a configurable timeout period (default is 10 seconds), the master replication agent returns a warning stating that it did not receive acknowledgement of the update from the subscriber and returns control of the thread to the application. The application is then free to commit another transaction to the master, which continues replication to the subscriber as before.

Return receipt transactions may time out for many reasons. The most likely causes for timeout are the network, a failed replication agent, or the master replication agent may be so far behind with respect to the transaction load that it cannot replicate the return receipt transaction before its timeout expires. For information on how to manage return-receipt timeouts, see "Managing return service timeout errors and replication state changes".

See "RETURN RECEIPT" for information on how to configure replication for return receipt.

Return twosafe replication

The return twosafe service provides fully synchronous replication between the master and subscriber. Unlike the previously described replication modes, where transactions are transmitted to the subscriber after being committed on the master, transactions in twosafe mode are first committed on the subscriber before they are committed on the master.

Figure 1-3 Return twosafe replication

The following describes the replication behavior between a master and subscriber configured for return twosafe replication:

1. The application commits the transaction on the master database.

2. The master replication agent writes the transaction records to the log and inserts a special precommit log record before the commit record. This precommit record acts as a place holder in the log until the master replication receives an acknowledgement that indicates the status of the commit on the subscriber.

Note:
Transmission of return twosafe transactions is nondurable, so the master replication agent does not flush the log records to disk before sending them to the subscriber, as it does by default when replication is configured for asynchronous or return receipt replication.

3. The master replication agent transmits the batch of update records to the subscriber.

4. The subscriber replication agent commits the transaction on the subscriber database.

5. The subscriber replication agent returns an acknowledgement back to the master replication agent with notification of whether the transaction was committed on the subscriber and whether the commit was successful.

6. If the commit on the subscriber was successful, the master replication agent commits the transaction on the master database.

7. The master replication agent returns control to the application.
If the subscriber is unable to acknowledge commit of the transaction within a configurable timeout period (default is 10 seconds) or if the acknowledgement from the subscriber indicates the commit was unsuccessful, the replication agent returns control to the application without committing the transaction on the master database. The application can then to decide whether to unconditionally commit or retry the commit. You can optionally configure your replication scheme to direct the master replication agent to commit all transactions that time out.

See "RETURN TWOSAFE" for information on how to configure replication for return twosafe.

Types of replication schemes

You create a replication scheme to define a specific configuration of master and subscriber databases. This section describes the possible relationships you can define between master and subscriber databases when creating a replication scheme.

When defining a relationship between a master and subscriber, consider these replication schemes:

- Active standby pair with read-only subscribers

- Classic replication

Active standby pair with read-only subscribers

Figure 1-4 shows an active standby pair replication scheme with an active master, a standby master, and four read-only subscriber databases.

Figure 1-4 Active standby pair

The active standby pair can replicate a whole database or select elements like tables and cache groups.

In an active standby pair, two databases are defined as masters. One is an active master, and the other is a standby master. The application updates the active master directly. Applications cannot update the standby master. It receives the updates from the active master and propagates the changes to as many as 127 read-only subscriber databases. This arrangement ensures that the standby master is always ahead of the subscriber databases and enables rapid failover to the standby master if the active master fails.

Only one of the master databases can function as an active master at a specific time. You can manage failover and recovery of an active standby pair with Oracle Clusterware. See Chapter 8, "Using Oracle Clusterware to Manage Active Standby Pairs". You can also manage failover and recovery manually. See Chapter 5, "Administering an Active Standby Pair without Cache Groups" or Chapter 6, "Administering an Active Standby Pair with Cache Groups."

If the standby master fails, the active master can replicate changes directly to the read-only subscribers. After the standby database has been recovered, it contacts the active master to receive any updates that have been sent to the subscribers while the standby master was down or was recovering. When the active master and the standby master have been synchronized, then the standby master resumes propagating changes to the subscribers.

For details about setting up an active standby pair, see "Setting up an active standby pair with no cache groups", "Setting up an active standby pair with a read-only cache group", or "Setting up an active standby pair with an AWT cache group."

Classic replication

Classic replication schemes enable you to design relationships between masters and subscribers. The following sections describe classic replication schemes:

- Full database replication or selective replication

- Unidirectional or bidirectional replication

- Direct replication or propagation

Full database replication or selective replication

Figure 1-5 illustrates a full replication scheme in which the entire master database is replicated to the subscriber.

Figure 1-5 Replicating the entire master database

You can also configure your master and subscriber databases to selectively replicate some elements in a master database to subscribers. Figure 1-6 shows examples of selective replication. The left side of the figure shows a master database that replicates the same selected elements to multiple subscribers, while the right side shows a master that replicates different elements to each subscriber.

Figure 1-6 Replicating selected elements to multiple subscribers

Unidirectional or bidirectional replication

Unidirectional replication is where a master database sends updates to one or more subscriber databases. Bidirectional replication is where there are two databases that operate bidirectionally, where each database is both a master and a subscriber.

These are basic ways to use bidirectional replication:

- Split workload configuration

- Distributed workload

Split workload configuration

In a split workload configuration, each database serves as a master for some elements and a subscriber for others.

Consider the example shown in Figure 1-7, where the accounts for Chicago are processed on database A while the accounts for New York are processed on database B.

Figure 1-7 Split workload bidirectional replication

Distributed workload

In a distributed workload replication scheme, user access is distributed across duplicate application/database combinations that replicate any update on any element to each other. In the event of a failure, the affected users can be quickly shifted to any application/database combination.The distributed workload configuration is shown in Figure 1-8. Users access duplicate applications on each database, which serves as both master and subscriber for the other database.

Figure 1-8 Distributed workload configuration

When databases are replicated in a distributed workload configuration, it is possible for separate users to concurrently update the same rows and replicate the updates to one another. Your application should ensure that such conflicts cannot occur, that they be acceptable if they do occur, or that they can be successfully resolved using the conflict resolution mechanism described in Chapter 13, "Resolving Replication Conflicts".

Note:
Do not use a distributed workload configuration with the return twosafe return service.

Direct replication or propagation

You can define a subscriber to serve as a propagator that receives replicated updates from a master and passes them on to subscribers of its own.

Propagators are useful for optimizing replication performance over lower-bandwidth network connections, such as those between servers in an intranet. For example, consider the direct replication configuration illustrated in Figure 1-9, where a master directly replicates to four subscribers over an intranet connection. Replicating to each subscriber over a network connection in this manner is an inefficient use of network bandwidth.

Figure 1-9 Master replicating directly to multiple subscribers over a network

For optimum performance, consider the configuration shown in Figure 1-10, where the master replicates to a single propagator over the network connection. The propagator in turn forwards the updates to each subscriber on its local area network.

Figure 1-10 Master replicating to a single propagator over a network

Propagators are also useful for distributing replication loads in configurations that involve a master database that must replicate to a large number of subscribers. For example, it is more efficient for the master to replicate to three propagators, rather than directly to the 12 subscribers as shown in Figure 1-11.

Figure 1-11 Using propagators to replicate to many subscribers

Note:
Each propagator is one-hop, which means that you can forward an update only once. You cannot have a hierarchy of propagators where propagators forward updates to other propagators.

Cache groups and replication

As described in Oracle TimesTen Application-Tier Database Cache User's Guide, a cache group is a group of tables stored in a central Oracle database that are cached in a local TimesTen Application-Tier Database Cache (TimesTen Cache). This section describes how cache groups can be replicated between TimesTen databases. You can achieve high availability by using an active standby pair to replicate asynchronous writethrough cache groups or read-only cache groups.

This section describes the following ways to replicate cache groups:

- Replicating an AWT cache group

- Replicating an AWT cache group with a subscriber propagating to an Oracle database

- Replicating a read-only cache group

See Chapter 6, "Administering an Active Standby Pair with Cache Groups" for details about configuring replication of cache groups.

Replicating an AWT cache group

An asynchronous writethrough (AWT) cache group can be configured as part of an active standby pair with optional read-only subscribers to ensure high availability and to distribute the application workload. Figure 1-12 shows this configuration.

Figure 1-12 AWT cache group replicated by an active standby pair

Application updates are made to the active database, the updates are replicated to the standby database, and then the updates are asynchronously written to the Oracle database by the standby. At the same time, the updates are also replicated from the standby to the read-only subscribers, which may be used to distribute the load from reading applications. The tables on the read-only subscribers are not in cache groups.

When there is no standby database, the active database both accepts application updates and writes the updates asynchronously to the Oracle database and the read-only subscribers. This situation can occur when the standby has not yet been created, or when the active fails and the standby becomes the new active. TimesTen reconfigures the AWT cache group when the standby becomes the new active.

If a failure occurs on the node where the active database resides, the standby node becomes the new active node. TimesTen automatically reconfigures the AWT cache group so that it can be updated directly by the application and continue to propagate the updates to the Oracle database asynchronously.

Replicating an AWT cache group with a subscriber propagating to an Oracle database

You can recover from a complete failure of a site by creating a special disaster recovery read-only subscriber on a remote site as part of the active standby pair replication configuration. Figure 1-13 shows this configuration.

Figure 1-13 Disaster recovery configuration with active standby pair

The standby database sends updates to cache group tables on the read-only subscriber. This special subscriber is located at a remote disaster recovery site and can propagate updates to a second Oracle database, also located at the disaster recovery site. You can set up more than one disaster recovery site with read-only subscribers and Oracle databases. See "Using a disaster recovery subscriber in an active standby pair".

Replicating a read-only cache group

A read-only cache group enforces caching behavior in which committed updates on the Oracle database tables are automatically refreshed to the corresponding TimesTen cache tables. Figure 1-14 shows a read-only cache group replicated by an active standby pair.

Figure 1-14 Read-only cache group replicated by an active standby pair

When the read-only cache group is replicated by an active standby pair, the cache group on the active database is autorefreshed from the Oracle database and replicates the updates to the standby, where AUTOREFRESH is also configured on the cache group but is in the PAUSED state. In the event of a failure of the active, TimesTen automatically reconfigures the standby to be autorefreshed when it takes over for the failed master database by setting the AUTOREFRESH STATE to ON.TimesTen also tracks whether updates that have been autorefreshed from the Oracle database to the active database have been replicated to the standby. This ensures that the autorefresh process picks up from the correct point after the active fails, and no autorefreshed updates are lost.This configuration may also include read-only subscriber databases.This enables the read workload to be distributed across many databases. The cache groups on the standby database replicate to regular (non-cache) tables on the subscribers.

Sequences and replication

In some replication configurations, you may need to keep sequences synchronized between two or more databases. For example, you may have a master database containing a replicated table that uses a sequence to fill in the primary key value for each row. The subscriber database is used as a hot backup for the master database. If updates to the sequence's current value are not replicated, insertions of new rows on the subscriber after the master has failed could conflict with rows that were originally inserted on the master.

TimesTen replication allows the incremented sequence value to be replicated to subscriber databases, ensuring that rows in this configuration inserted on either database does not conflict. See "Replicating sequences" for details on writing a replication scheme to replicate sequences.

Foreign keys and replication

You may choose to replicate all or a subset of tables that have foreign key relationships with one another. However, the method for how to replicate the tables involved in the relationship differ according to the type of replication scheme. See the following for details:

- "Replicating tables with foreign key relationships in an active standby pair"

- "Replicating tables with foreign key relationships in a classic replication scheme"

Aging and replication

When a table or cache group is configured with least recently used (LRU) or time-based aging, the following rules apply to the interaction with replication:

- The aging configuration on replicated tables and cache groups must be identical on every peer database.

- If the replication scheme is an active standby pair, then aging is performed only on the active database. Deletes that result from aging are then replicated to the standby database. The aging configuration must be set to ON on both the active and standby databases. TimesTen automatically determines which database is actually performing the aging based on its current role as active or standby.

- In a replication scheme that is not an active standby pair, aging is performed individually in each database. Deletes performed by aging are not replicated to other databases.

- When an asynchronous writethrough cache group is in a database that is replicated by an active standby pair, delete operations that result from aging are not propagated to the Oracle database.

2 Getting Started

The following sections describe how to configure and start up sample replication schemes:

- Configuring an active standby pair with one subscriber

- Configuring a replication scheme with one master and one subscriber

Note:
You must have the ADMIN privilege to complete the procedures in this chapter.

Configuring an active standby pair with one subscriber

This section describes how to create an active standby pair with one subscriber. The active database is master1. The standby database is master2. The subscriber database is subscriber1. To keep the example simple, all databases reside on the same computer, server1.

Figure 2-1 shows this configuration.

Figure 2-1 Active standby pair with one subscriber

This section includes the following topics:

- Step 1: Create the DSNs for the master and the subscriber databases

- Step 2: Create a table in one of the master databases

- Step 3: Define the active standby pair

- Step 4: Start the replication agent on a master database

- Step 5: Set the state of a master database to 'ACTIVE'

- Step 6. Create a user on the active database

- Step 7: Duplicate the active database to the standby database

- Step 8: Start the replication agent on the standby database

- Step 9. Duplicate the standby database to the subscriber

- Step 10: Start the replication agent on the subscriber

- Step 11: Insert data into the table on the active database

- Step 12: Drop the active standby pair and the table

Step 1: Create the DSNs for the master and the subscriber databases

Create DSNs named master1, master2 and subscriber1 as described in "Managing TimesTen Databases" in Oracle TimesTen In-Memory Database Operations Guide.

On UNIX systems, use a text editor to create the following odbc.ini file:

[master1]
DRIVER=install_dir/lib/libtten.so
DataStore=/tmp/master1
DatabaseCharacterSet=AL32UTF8
ConnectionCharacterSet=AL32UTF8

[master2]
DRIVER=install_dir/lib/libtten.so
DataStore=/tmp/master2
DatabaseCharacterSet=AL32UTF8
ConnectionCharacterSet=AL32UTF8

[subscriber1]
DRIVER=install_dir/lib/libtten.so
DataStore=/tmp/subscriber1
DatabaseCharacterSet=AL32UTF8
ConnectionCharacterSet=AL32UTF8

On Windows, use the ODBC Administrator to set the same connection attributes. Use defaults for all other settings.

Step 2: Create a table in one of the master databases

Use the ttIsql utility to connect to the master1 database:

% ttIsql master1

Copyright (c) 1996-2011, Oracle.  All rights reserved.
Type ? or "help" for help, type "exit" to quit ttIsql.

connect "DSN=master1";
Connection successful: DSN=master1;UID=timesten;DataStore=/tmp/master1;
DatabaseCharacterSet=AL32UTF8;ConnectionCharacterSet=AL32UTF8;TypeMode=0;
(Default setting AutoCommit=1)
Command>

Create the employees table;

Command> CREATE TABLE employees
>   ( employee_id   NUMBER(6) PRIMARY KEY,
>    first_name     VARCHAR2(20),
>    last_name      VARCHAR2(25) NOT NULL,
>    email          VARCHAR2(25) NOT NULL UNIQUE,
>    phone_number   VARCHAR2(20),
>    hire_date      DATE NOT NULL,
>    job_id         VARCHAR2(10) NOT NULL,
>    salary         NUMBER(8,2),
>    commission_pct NUMBER(2,2),
>    manager_id     NUMBER(6),
>    department_id  NUMBER(4)
> ) ;

Step 3: Define the active standby pair

Define the active standby pair on master1:

Command> CREATE ACTIVE STANDBY PAIR master1, master2
> SUBSCRIBER subscriber1;

For more information about defining an active standby pair, see Chapter 3, "Defining an Active Standby Pair Replication Scheme".

Step 4: Start the replication agent on a master database

Start the replication agent on master1:

Command> CALL ttRepStart;

Step 5: Set the state of a master database to 'ACTIVE'

The state of a new database in an active standby pair is 'IDLE' until the active database has been set.

Use the ttRepStateSet built-in procedure to designate master1 as the active database:

Command> CALL ttRepStateSet('ACTIVE');

Verify the state of master1:

Command> CALL ttRepStateGet;
< ACTIVE, NO GRID >
1 row found.

Step 6. Create a user on the active database

Create a user ttuser with a password of ttuser and grant ttuser the ADMIN privilege. Creating a user with the ADMIN privilege is required by Access Control for the next step.

Command> CREATE USER ttuser IDENTIFIED BY ttuser;
User created.
Command> GRANT ADMIN TO ttuser;

Step 7: Duplicate the active database to the standby database

Exit ttIsql and use the ttRepAdmin utility as the ttuser (the user created with the ADMIN privilege) with the -duplicate option to duplicate the active database to the standby database. If you are using two different hosts, enter the ttRepAdmin command from the target host.

% ttRepAdmin -duplicate -from master1 -host server1 -uid ttuser -pwd ttuser
master2

Step 8: Start the replication agent on the standby database

Use ttIsql to connect to the master2 database and start the replication agent:

% ttIsql master2
Copyright (c) 1996-2011, Oracle.  All rights reserved.
Type ? or "help" for help, type "exit" to quit ttIsql.

connect "DSN=master2";
Connection successful: DSN=master2;UID=timesten;DataStore=/tmp/master2;
DatabaseCharacterSet=AL32UTF8;ConnectionCharacterSet=AL32UTF8;TypeMode=0;
(Default setting AutoCommit=1)

Command> CALL ttRepStart;

Starting the replication agent for the standby database automatically sets its state to 'STANDBY'. Verify the state of master2:

Command> CALL ttRepStateGet;
< STANDBY, NO GRID >
1 row found.

Step 9. Duplicate the standby database to the subscriber

Exit ttIsql and use the ttRepAdmin utility as the ttuser (the user created with the ADMIN privilege) to duplicate the standby database to the subscriber database:

% ttRepAdmin -duplicate -from master2 -host server1 -uid ttuser -pwd ttuser
subscriber1

Step 10: Start the replication agent on the subscriber

Use ttIsql to connect to subscriber1 and start the replication agent. Verify the state of subscriber1. Starting the replication agent for the subscriber database automatically sets its state to 'IDLE'. All subscriber databases have their state set to 'IDLE'.

% ttIsql subscriber1

Copyright (c) 1996-2011, Oracle.  All rights reserved.
Type ? or "help" for help, type "exit" to quit ttIsql.

connect "DSN=subscriber1";
Connection successful: DSN=subscriber1;UID=timesten;DataStore=/stmp/subscriber1;
DatabaseCharacterSet=AL32UTF8;ConnectionCharacterSet=AL32UTF8;TypeMode=0;
(Default setting AutoCommit=1)

Command> CALL ttRepStart;

Command> call ttRepStateGet;
< IDLE, NO GRID >
1 row found.

Step 11: Insert data into the table on the active database

Use the ttIsql utility to connect to the master1 database:

% ttIsql master1

Copyright (c) 1996-2011, Oracle.  All rights reserved.
Type ? or "help" for help, type "exit" to quit ttIsql.

connect "DSN=master1";
Connection successful: DSN=master1;UID=timesten;DataStore=/tmp/master1;
DatabaseCharacterSet=AL32UTF8;ConnectionCharacterSet=AL32UTF8;TypeMode=0;
(Default setting AutoCommit=1)
Command>

Insert a row into the employees table on master1.

Command> INSERT INTO employees VALUES
> ( 202,
>   'Pat',
>   'Fay',
>   'PFAY',
>   '603-123-7777',
>   TO_DATE('17-AUG-1997', 'dd-MON-yyyy'),
>   'MK_REP',
>   6000,
>   NULL,
>   201,
>   20
);
1 row inserted.
Command> SELECT * FROM employees;
< 202, Pat, Fay, PFAY, 603-123-7777, 1997-08-17 00:00:00, MK_REP,
6000, <NULL>, 201, 20 >
1 row found.

Verify that the insert is replicated to master2 and subscriber1. Use ttIsql to connect to master2:

% ttIsql master2
Copyright (c) 1996-2011, Oracle.  All rights reserved.
Type ? or "help" for help, type "exit" to quit ttIsql.

connect "DSN=master2";
Connection successful: DSN=master2;UID=timesten;DataStore=/tmp/master2;
DatabaseCharacterSet=AL32UTF8;ConnectionCharacterSet=AL32UTF8;TypeMode=0;
(Default setting AutoCommit=1)

Verify that the data is replicated to master2:

Command> SELECT * FROM employees;
< 202, Pat, Fay, PFAY, 603-123-7777, 1997-08-17 00:00:00, MK_REP,
6000, <NULL>, 201, 20 >
1 row found.

Perform the same step on subscriber1 to verify the data is replicated to the subscriber.

Step 12: Drop the active standby pair and the table

Connect to each database using ttIsql and stop the replication agents on each database:

Command> CALL ttRepStop;

Drop the active standby pair on each database. You can then drop the employees table on any database in which you have dropped the active standby pair.

Command> DROP ACTIVE STANDBY PAIR;

Command> DROP TABLE employees;

Configuring a replication scheme with one master and one subscriber

This section describes how to configure a replication scheme that replicates the contents of a single table in a master database (masterds) to a table in a subscriber database (subscriberds). To keep the example simple, both databases reside on the same computer.

Figure 2-2 Simple replication scheme

This section includes the following topics:

- Step 1: Create the DSNs for the master and the subscriber

- Step 2: Create a table and replication scheme on the master database

- Step 3: Create a table and replication scheme on the subscriber database

- Step 4: Start the replication agent on each database

- Step 5: Insert data into the table on the master database

- Step 6: Drop the replication scheme and table

Step 1: Create the DSNs for the master and the subscriber

Create DSNs named masterds and subscriberds as described in "Managing TimesTen Databases" in Oracle TimesTen In-Memory Database Operations Guide.

On UNIX systems, use a text editor to create the following odbc.ini file on each database:

[masterds]
DataStore=/tmp/masterds
DatabaseCharacterSet=AL32UTF8
ConnectionCharacterSet=AL32UTF8

[subscriberds]
DataStore=/tmp/subscriberds
DatabaseCharacterSet=AL32UTF8
ConnectionCharacterSet=AL32UTF8

On Windows, use the ODBC Administrator to set the same connection attributes. Use defaults for all other settings.

Step 2: Create a table and replication scheme on the master database

Connect to masterds with the ttIsql utility:

% ttIsql masterds
Copyright (c) 1996-2011, Oracle.  All rights reserved.
Type ? or "help" for help, type "exit" to quit ttIsql.

connect "DSN=masterds";
Connection successful: DSN=masterds;UID=timesten;
DataStore=/tmp/masterds;DatabaseCharacterSet=AL32UTF8;
ConnectionCharacterSet=AL32UTF8;TypeMode=0;
(Default setting AutoCommit=1)
Command>

Create the employees table:

Command> CREATE TABLE employees
>   ( employee_id   NUMBER(6) PRIMARY KEY,
>    first_name     VARCHAR2(20),
>    last_name      VARCHAR2(25) NOT NULL,
>    email          VARCHAR2(25) NOT NULL UNIQUE,
>    phone_number   VARCHAR2(20),
>    hire_date      DATE NOT NULL,
>    job_id         VARCHAR2(10) NOT NULL,
>    salary         NUMBER(8,2),
>    commission_pct NUMBER(2,2),
>    manager_id     NUMBER(6),
>    department_id  NUMBER(4)
> ) ;

Create a replication scheme called repscheme to replicate the employees table from masterds to subscriberds.

Command> CREATE REPLICATION repscheme
> ELEMENT e TABLE employees
> MASTER masterds
> SUBSCRIBER subscriberds;

Step 3: Create a table and replication scheme on the subscriber database

Connect to subscriberds and create the same table and replication scheme, using the same procedure described in Step 2.

Step 4: Start the replication agent on each database

Start the replication agents on masterds and subscriberds:

Command> call ttRepStart;

Exit ttIsql. Use the ttStatus utility to verify that the replication agents are running for both databases:

% ttStatus
TimesTen status report as of Thu Aug 11 17:05:23 2011

Daemon pid 18373 port 4134 instance ttuser
TimesTen server pid 18381 started on port 4136
------------------------------------------------------------------------
Data store /tmp/masterds
There are 16 connections to the data store
Shared Memory KEY 0x0201ab43 ID 5242889
PL/SQL Memory KEY 0x0301ab43 ID 5275658 Address 0x10000000
Type            PID     Context     Connection Name              ConnID
Process         20564   0x081338c0  masterds                          1
Replication     20676   0x08996738  LOGFORCE                          5
Replication     20676   0x089b69a0  REPHOLD                           2
Replication     20676   0x08a11a58  FAILOVER                          3
Replication     20676   0x08a7cd70  REPLISTENER                       4
Replication     20676   0x08ad7e28  TRANSMITTER                       6
Subdaemon       18379   0x080a11f0  Manager                        2032
Subdaemon       18379   0x080fe258  Rollback                       2033
Subdaemon       18379   0x081cb818  Checkpoint                     2036
Subdaemon       18379   0x081e6940  Log Marker                     2035
Subdaemon       18379   0x08261e70  Deadlock Detector              2038
Subdaemon       18379   0xae100470  AsyncMV                        2040
Subdaemon       18379   0xae11b508  HistGC                         2041
Subdaemon       18379   0xae300470  Aging                          2039
Subdaemon       18379   0xae500470  Flusher                        2034
Subdaemon       18379   0xae55b738  Monitor                        2037
Replication policy  : Manual
Replication agent is running.
Cache Agent policy  : Manual
PL/SQL enabled.
------------------------------------------------------------------------
Data store /tmp/subscriberds
There are 16 connections to the data store
Shared Memory KEY 0x0201ab41 ID 5177351
PL/SQL Memory KEY 0x0301ab41 ID 5210120 Address 0x10000000
Type            PID     Context     Connection Name              ConnID
Process         20594   0x081338f8  subscriberds                      1
Replication     20691   0x0893c550  LOGFORCE                          5
Replication     20691   0x089b6978  REPHOLD                           2
Replication     20691   0x08a11a30  FAILOVER                          3
Replication     20691   0x08a6cae8  REPLISTENER                       4
Replication     20691   0x08ad7ba8  RECEIVER                          6
Subdaemon       18376   0x080b1450  Manager                        2032
Subdaemon       18376   0x0810e4a8  Rollback                       2033
Subdaemon       18376   0x081cb8b0  Flusher                        2034
Subdaemon       18376   0x08246de0  Monitor                        2035
Subdaemon       18376   0x082a20a8  Deadlock Detector              2036
Subdaemon       18376   0x082fd370  Checkpoint                     2037
Subdaemon       18376   0x08358638  Aging                          2038
Subdaemon       18376   0x083b3900  Log Marker                     2040
Subdaemon       18376   0x083ce998  AsyncMV                        2039
Subdaemon       18376   0x08469e90  HistGC                         2041
Replication policy  : Manual
Replication agent is running.
Cache Agent policy  : Manual
PL/SQL enabled.

Step 5: Insert data into the table on the master database

Use ttIsql to connect to the master database and insert some rows into the employees table:

% ttIsql masterds
Command> INSERT INTO employees VALUES
> ( 202,
>   'Pat',
>   'Fay',
>   'PFAY',
>   '603-123-7777',
>   TO_DATE('17-AUG-1997', 'dd-MON-yyyy'),
>   'MK_REP',
>   6000,
>   NULL,
>   201,
>   20
);
1 row inserted.

Open a second command prompt window for the subscriber. Connect to the subscriber database and check the contents of the employees table:

% ttIsql subscriberds
Command> SELECT * FROM employees;
< 202, Pat, Fay, PFAY, 603-123-7777, 1997-08-17 00:00:00, MK_REP,
6000, <NULL>, 201, 20 >
1 row found.

Figure 2-3 shows that the rows that are inserted into masterds are replicated to subscriberds.

Figure 2-3 Replicating changes to the subscriber database

Step 6: Drop the replication scheme and table

After you have completed your replication tests, stop the replication agents on both masterds and subscriberds:

Command> CALL ttRepStop;

To remove the employees table and repscheme replication scheme from the master and subscriber databases, enter these statements on each database:

Command> DROP REPLICATION repscheme;
Command> DROP TABLE employees;

3 Defining an Active Standby Pair Replication Scheme

The following sections describe how to design a highly available system and define replication schemes:

- Overview of master database states

- Duplicating a database

- Restrictions on active standby pairs

- Defining the DSNs for the databases

- Table requirements for active standby pairs

- Defining an active standby pair replication scheme

- Identifying the databases in the active standby pair

- Using a return service for an active standby pair

- Setting STORE attributes for an active standby pair

- Configuring network operations for an active standby pair

- Using automatic client failover for an active standby pair

- Including or excluding database objects from replication

- Replicating tables with foreign key relationships in an active standby pair

- Materialized views in an active standby pair

- Replicating sequences in an active standby pair

To reduce the amount of bandwidth required for replication, see "Compressing replicated traffic".

Overview of master database states

This section summarizes the possible states of a master database. These states are referenced in the tasks described in the rest of the chapter.

The master databases can be in one of the following states:

- ACTIVE - A database in this state is the active database. Applications can update its replicated tables.

- STANDBY - A database in this state is the standby database. Applications can update only nonreplicated tables in the standby database. Nonreplicated tables are tables that have been excluded from the replication scheme by using the EXCLUDE TABLE or EXCLUDE CACHE GROUP clauses of the CREATE ACTIVE STANDBY PAIR statement.

- FAILED - A database in this state is a failed master database. No updates can be replicated to it.

- IDLE - A database in this state has not yet had its role in the active standby pair assigned. It cannot be updated. Every database comes up in the IDLE state.

- RECOVERING - When a previously failed master database is synchronizing updates with the active database, it is in the RECOVERING state.

You can use the ttRepStateGet built-in procedure to discover the state of a master database.

Duplicating a database

When you set up a replication scheme or administer a recovery, a common task is to duplicate a database. Use the -duplicate option of the ttRepAdmin utility or the ttRepDuplicateEx C function to duplicate a database.

To duplicate a database, these conditions must be fulfilled:

- The instance administrator performs the duplicate operation.

- The instance administrator user name must be the same on both instances involved in the duplication.

- You must provide the user name and password for a user with the ADMIN privilege on the source database.

- The target DSN cannot include client/server attributes.

On the source database, create a user and grant the ADMIN privilege to the user:

Command> CREATE USER ttuser IDENTIFIED BY ttuser;
User created.

Command> GRANT ADMIN TO ttuser;

Assume the user name of the instance administrator is timesten. Logged in as timesten on the target host, duplicate the dsn1 database on host1 to dsn2:

ttRepAdmin -duplicate -from dsn1 -host host1 dsn2

Enter internal UID at the remote datastore with ADMIN privileges: ttuser
Enter password of the internal Uid at the remote datastore:

Enter ttuser when prompted for the password of the internal user at the remote database.

If you want to use a specific local or remote network interface over which the database duplication occurs, you can optionally specify either by providing an alias or the IP address of the network interface. You can specify the local and remote network interfaces for the source and target hosts by using the -localIP and -remoteIP options of ttRepAdmin -duplicate. If you do not specify one or both network interfaces, TimesTen chooses them.

If you are duplicating an active database that has cache groups, use the -keepCG option. You must also specify the cache administration user name and password with the -cacheUid and -cachePwd options. If you do not provide the cache administration user password, ttRepAdmin prompts for a password. If the cache administration user name is orauser and the password is orapwd, duplicate database dsn1 on host1:

ttRepAdmin -duplicate -from dsn1 -host host1 -keepCG
-connStr "DSN=dsn2;UID=;PWD="

Enter internal UID at the remote datastore with ADMIN privileges: ttuser
Enter password of the internal Uid at the remote datastore:

Enter ttuser when prompted for the password. The ttRepAdmin utility then prompts for the cache administration user and password:

Enter cache administrator UID: orauser
Enter cache administrator password:

Enter orapwd when prompted for the cache administration password.

The UID and PWD for dsn2 are specified as null values in the connection string so that the connection is made as the current OS user, which is the instance administrator. Only the instance administrator can run ttRepAdmin -duplicate. If dsn2 is configured with PWDCrypt instead of PWD, then the connection string should be "DSN=dsn2;UID=;PWDCrypt=".

When you duplicate a standby database with cache groups to a read-only subscriber, use the -nokeepCG option. In this example, dsn2 is the standby database and sub1 is the read-only subscriber:

ttRepAdmin -duplicate -from dsn2 -host host2 -nokeepCG
-connStr "DSN=sub1;UID=;PWD="

The ttRepAdmin utility prompts for values for -uid and -pwd.

If you cannot access the Oracle database (either the Oracle database is down or you cannot connect to it) while performing a duplicate for a replication scheme with AWT or incremental autorefresh cache groups, then the ttRepAdmin -duplicate command cannot update the metadata on the Oracle database (that cache uses to manage AWT and autorefresh cache groups) after AWT or incremental autorefresh cache groups are duplicated. In this case, use one of the following options to perform the duplicate:

- If you are using ttRepAdmin -duplicate to recover either a failed active or standby master where all AWT or incremental autorefresh cache groups are included in the active standby pair replication scheme, then use the -keepCG -recoveringNode options. When this option is used, changes that occur during the duplicate operation are tracked and so may not need to initiate a full autorefresh.

- Otherwise, use the -keepCG -deferCacheUpdate options. This option may initiate a full autorefresh.

After completion of the duplicate operation with either -keepCG -recoveringNode options or -keepCG -deferCacheUpdate options, warning messages are posted informing you that while the duplicate operation was successful, updates to the Oracle database metadata are deferred until the cache and replication agents are started. Thus, once the duplicate operation is complete, start both the cache and replication agents on the new node. If there are cascading TimesTen node failures and intermittent connectivity problems with the Oracle database, then starting the cache and replication agents may initiate a full autorefresh.

For more information about the ttRepAdmin utility, see "ttRepAdmin" in Oracle TimesTen In-Memory Database Reference. For more information about the ttRepDuplicateEx C function, see "ttRepDuplicateEx" in Oracle TimesTen In-Memory Database C Developer's Guide.

Restrictions on active standby pairs

When you are planning an active standby pair, keep in mind the following:

- For the initial setup, you create the standby database by duplicating the active database with the ttRepAdmin -duplicate utility or the ttRepDuplicateEx C function.

- To ensure high availability, each active and standby master databases as well as all subscriber databases should be on different machines.

- To avoid performance issues, especially in intensive operations such as a master database catchup, standby master recovery, or processing a return service, we strongly recommend that the network has a latency of less than 100 milliseconds between the hosts on which the master databases are installed.

Note:
When using return services, the active master waits for a response from the standby master. If the bandwidth causes the latency response time to exceed the defined timeout, the performance of the transaction is negatively affected. For more information on the timeout period for return services, see "Setting the return service timeout period".

- The clock skew between the active node and the standby node cannot exceed 250 milliseconds. When adjusting the system clocks on any nodes to be synchronized with each other, do not set any clock backward in time.

- ALTER ACTIVE STANDBY PAIR statements can be executed only on the active database. If ALTER ACTIVE STANDBY PAIR is executed on the active database, then the standby database must be regenerated by duplicating the active database. All subscribers must also be regenerated from the standby database. See "Duplicating a database".

- Read-only subscribers can be created only by duplicating the standby database. If the standby database is unavailable, then the read-only subscribers can be created by duplicating the active database. See "Duplicating a database".

- You can specify at most 127 subscriber databases.

- Replication from the standby database to the read-only subscribers occurs asynchronously.

- Writes on replicated tables are not allowed on the standby database or the subscriber databases. However, operations on sequences and XLA bookmarks are allowed on the standby database and the subscriber databases. Reads are also allowed.

- After failover, the new standby database can only be recovered from the active database by duplicating the active database unless return twosafe replication is used between the active and the standby databases. If return twosafe replication is used, the automated master catch-up feature may be used instead. See "Automatic catch-up of a failed master database".

- You cannot replicate a temporary database.

- You cannot replicate tables with compressed columns.

Defining the DSNs for the databases

Before you define the active standby pair, define the DSNs for the active, standby, and read-only subscriber databases. On UNIX, create an odbc.ini file. On Windows, use the ODBC Administrator to name the databases and set connection attributes. See "Step 1: Create the DSNs for the master and the subscriber databases" for an example.

Each database "name" specified in a replication scheme must match the prefix of the database file name (without the path) given for the DataStore data store attribute in the DSN definition for the database. To avoid confusion, use the same name for both the DataStore and Data Source Name data store attributes in each DSN definition. Values for DataStore are case-sensitive. For example, if the database path is directory/subdirectory/foo.ds0, then foo is the database name that you should use.

Table requirements for active standby pairs

Before you can create an active standby pair, you must create an object to be replicated.

Tables that are replicated in an active standby pair must have one of the following:

- A primary key

- A unique index over non-nullable columns

Replication uses the primary key or unique index to identify each row in the replicated table. Replication always selects the first usable index that turns up in a sequential check of the table's index array. If there is no primary key, replication selects the first unique index without NULL columns it encounters. The selected index on the replicated table in the active database must also exist on its counterpart table in the standby database.

Note:
The keys on replicated tables are transmitted in each update record to the subscribers. Smaller keys are transmitted more efficiently.

Replicated tables have these data type restrictions:

- VARCHAR2, NVARCHAR2, VARBINARY and TT_VARCHAR columns in replicated tables are limited to a size of 4 megabytes. For a VARCHAR2 column, the maximum length when using character length semantics depends on the number of bytes each character occupies when using a particular database character set. For example, if the character set requires four bytes for each character, the maximum possible length is one million characters. For an NVARCHAR2 column, which requires two bytes for each character, the maximum length when using character length semantics is two million characters.

- Columns with the BLOB data type in replicated tables are limited to a size of 16 megabytes. Columns with the CLOB or NCLOB data type in replicated tables are limited to a size of 4 megabytes.

- A primary key column cannot have a LOB data type.

You cannot replicate tables with compressed columns.

Defining an active standby pair replication scheme

Use the CREATE ACTIVE STANDBY PAIR SQL statement to create an active standby pair replication scheme. You must have the ADMIN privilege to use the CREATE ACTIVE STANDBY PAIR statement and to perform other replication operations. Only the instance administrator can duplicate databases.

Note:
See "Step 3: Define the active standby pair" for an example. See "CREATE ACTIVE STANDBY PAIR" for the complete syntax in the Oracle TimesTen In-Memory Database SQL Reference.

Table 3-1 shows the components of the CREATE ACTIVE STANDBY PAIR statement that are used to create the active standby pair replication scheme. Each component is described with the identified topics in this chapter.

Table 3-1 Components of an active standby pair replication scheme

Component

See...

CREATE ACTIVE STANDBY PAIR FullDatabaseName, FullDatabaseName

"Identifying the databases in the active standby pair"

[ReturnServiceAttribute]

"Using a return service"

[SUBSCRIBER FullDatabaseName [,...]]

"Identifying the databases in the active standby pair"

[STORE FullDatabaseName [StoreAttribute [...]]]

"Setting STORE attributes"

[NetworkOperation [...]]

"Configuring network interfaces with the ROUTE clause"

[{INCLUDE|EXCLUDE}

{TABLE [[Owner.]TableName[,...]]|

CACHE GROUP [[Owner.]CacheGroupName[,...]|

SEQUENCE [[Owner.]SequenceName[,...]]}

[,...]]

"Including or excluding database objects from replication"

Identifying the databases in the active standby pair

The first component identifies the active database, standby database, and any subscriber databases. The first database name designates the active database. The second database name designates the standby database. Read-only subscriber databases are indicated by the SUBSCRIBER clause.

Use the full database name described in "Defining the DSNs for the databases".

Command> CREATE ACTIVE STANDBY PAIR master1, master2
> SUBSCRIBER subscriber1;

The active database and the standby database should be on separate hosts to achieve a highly available system. Read-only subscribers can be either local or remote. A remote subscriber provides protection from site-specific disasters.

You can also specify the hosts where the databases reside by using an IP address or a literal host name surrounded by double quotes. Provide a host ID as part of FullDatabaseName:

DatabaseName [ON Host]

Host can be either an IP address or a literal host name. Use the value returned by the hostname operating system command. It is good practice to surround a host name with double quotes. For example:

Command> CREATE ACTIVE STANDBY PAIR
> repdb1 ON "host1",
> repdb2 ON "host2";

Using a return service for an active standby pair

You can configure your replication scheme with a return service to ensure a higher level of confidence that your replicated data is consistent on the active and standby databases. For full details on how to configure a return service for your replication scheme, see "Using a return service".

Setting STORE attributes for an active standby pair

The STORE attributes clause in either the CREATE ACTIVE STANDBY PAIR or ALTER ACTIVE STANDBY PAIR statements are used to set optional behavior for return services, compression, timeouts, durable commit behavior, and table definition checking. See "CREATE ACTIVE STANDBY PAIR" in the Oracle TimesTen In-Memory Database SQL Reference for a full description of STORE attributes.

Note:
If you are using ALTER ACTIVE STANDBY PAIR to change any of the STORE attributes, you must follow the steps described in "Making other changes to an active standby pair".

See "Setting STORE attributes" for more details on how to use and configure the STORE attributes for an active standby pair.

Configuring network operations for an active standby pair

If a replication host has more than one network interface, you may want to configure replication to use an interface other than the default interface. For details, see "Configuring network interfaces with the ROUTE clause".

Using automatic client failover for an active standby pair

Automatic client failover is for use in High Availability scenarios with a TimesTen active standby pair replication configuration. If failure of the active TimesTen node results in the original standby node becoming the new active node, then automatic client failover feature automatically transfers the application connection to the new active node.

For full details on how to configure and use automatic client failover, see "Using automatic client failover" in the Oracle TimesTen In-Memory Database Operations Guide.

Note:
Automatic client failover is complementary to Oracle Clusterware in situations where Oracle Clusterware is used, but the two features are not dependent on each other. For information about Oracle Clusterware, you can refer to Chapter 8, "Using Oracle Clusterware to Manage Active Standby Pairs".

Including or excluding database objects from replication

An active standby pair replicates an entire database by default. Use the INCLUDE clause to replicate only the tables, cache groups and sequences that are listed in the INCLUDE clause. No other database objects are replicated in an active standby pair that is defined with an INCLUDE clause. For example, this INCLUDE clause specifies three tables to be replicated by the active standby pair:

INCLUDE TABLE employees, departments, jobs

You can choose to exclude specific tables, cache groups or sequences from replication by using the EXCLUDE clause of the CREATE ACTIVE STANDBY PAIR statement. Use one EXCLUDE clause for each object type. For example:

EXCLUDE TABLE ttuser.tab1, ttuser.tab2
EXCLUDE CACHE GROUP ttuser.cg1, ttuser.cg2
EXCLUDE SEQUENCE ttuser.seq1, ttuser.seq2

Note:
Sequences with the CYCLE attribute cannot be replicated.

Replicating tables with foreign key relationships in an active standby pair

With the active standby pair replication scheme, you may choose to replicate all or a subset of tables that have foreign key relationships with one another. You can create the tables and the foreign key relationship on the active master either before or after the active standby pair replication scheme is created.

- Before creation of active standby pair: You can create the tables and the foreign key relationship on the active master before the active standby pair replication scheme is created. Then, create the active standby pair replication scheme.

- After creation of active standby pair: You can create the tables and the foreign key relationship on the active master after the active standby pair replication scheme is created. In order for the tables to be automatically replicated to the standby master and added to the replication scheme, you must be using the default mode where DDLReplicationLevel is set to 2 or larger and DDLReplicationAction='INCLUDE'.

If a child table with a foreign key defines ON DELETE CASCADE, then you must replicate any other table with a foreign key relationship to the child table. This requirement prevents foreign key conflicts from occurring on the standby master tables when a cascade deletion occurs on the active master database.

TimesTen replicates a cascade deletion as a single operation, rather than replicating to the subscriber each individual row deletion which occurs on the child table when a row is deleted on the parent. As a result, any row on the child table on the subscriber database, which contains the foreign key value that was deleted on the parent table, is also deleted, even if that row did not exist on the child table on the master database.

Materialized views in an active standby pair

When you replicate a database containing a materialized or nonmaterialized view, only the detail tables associated with the view are replicated. The view itself is not replicated. A matching view can be defined on the standby database, but it is not required. If detail tables are replicated, TimesTen automatically updates the corresponding view. However, TimesTen replication verifies only that the replicated detail tables have the same structure on both databases. It does not enforce that the materialized views are the same on each database.

Replicating sequences in an active standby pair

Sequences are replicated unless you exclude them from the active standby pair or unless they have the CYCLE attribute. See "Including or excluding database objects from replication". Replication of sequences is optimized by reserving a range of sequence numbers on the standby database each time a sequence is updated on the active database. Reserving a range of sequence numbers reduces the number of updates to the transaction log. The range of sequence numbers is called a cache. Sequence updates on the active database are replicated only when they are followed by or used in replicated transactions.

Consider a sequence named my.sequence with a MINVALUE of 1, an INCREMENT of 1 and the default Cache of 20. The very first time that you reference my.sequence.NEXTVAL, the current value of the sequence on the active database is changed to 2, and a new current value of 21 (20+1) is replicated to the standby database. The next 19 references to my.seq.NEXTVAL on the active database result in no new current value being replicated, because the current value of 21 on the standby database is still ahead of the current value on the active database. On the twenty-first reference to my.seq.NEXTVAL, a new current value of 41 (21+20) is transmitted to the standby database because the previous current value of 21 on the standby database is now behind the value of 22 on the active database.

Operations on sequences such as SELECT my.seq.NEXTVAL FROM sys.dual, while incrementing the sequence value, are not replicated until they are followed by transactions on replicated tables. A side effect of this behavior is that these sequence updates are not purged from the log until followed by transactions on replicated tables. This causes ttRepSubscriberWait and ttRepAdmin -wait to fail when only these sequence updates are present at the end of the log.

4 Defining Attributes and Options for a Replication Scheme

The following sections describe the return service options, STORE atttributes, and network operations that can be configured for both active standby pairs and classic replication (involving master and subscribers). Any differences for one replication scheme over the other are detailed within each section.

- Using a return service

- Setting STORE attributes

- Configuring the network

Using a return service

You can configure your replication scheme with a return service to ensure a higher level of confidence that your replicated data is consistent on the databases in your replication scheme.

Note:
This section assumes you understand return services. For an overview on return services, see "Copying updates between databases".

This section describes how to configure and manage the return receipt and return twosafe services. You can specify a return service for table elements and database elements for any standby or subscriber defined in replication scheme with the CREATE ACTIVE STANDBY PAIR, ALTER ACTIVE STANDBY PAIR, CREATE REPLICATION, or ALTER REPLICATION statements. The default is the NO RETURN service, which is asynchronous replication and the best performance option.

Note:
You can use the ttRepXactStatus procedure to check on the status of a return receipt or return twosafe transaction. See "Check the status of return service transactions" for details.

The following sections describe the return services that can be used for your replication scheme:

- Specifying a different return service for each subscriber in a classic replication scheme

- RETURN RECEIPT

- RETURN RECEIPT BY REQUEST

- RETURN TWOSAFE

- RETURN TWOSAFE BY REQUEST

- NO RETURN

Specifying a different return service for each subscriber in a classic replication scheme

In a classic replication scheme, you can specify a different return service for table elements and database elements for the subscribers listed in each SUBSCRIBER clause in a CREATE REPLICATION or ALTER REPLICATION statement.

Example 4-1 shows separate SUBSCRIBER clauses that can define different return service attributes for SubDatabase1 and SubDatabase2.

Example 4-1 Different return services for each subscriber

CREATE REPLICATION Owner.SchemeName
ELEMENT ElementNameElementType
MASTER DatabaseName ON "HostName"
SUBSCRIBER SubDatabase1 ON "HostName" ReturnServiceAttribute1
SUBSCRIBER SubDatabase2 ON "HostName" ReturnServiceAttribute2;

Alternatively, you can specify the same return service attribute for all of the subscribers defined in an element. Example 4-2 shows the use of a single SUBSCRIBER clause that defines the same return service attributes for both SubDatabase1 and SubDatabase2.

Example 4-2 Same return service for all subscribers

CREATE REPLICATION Owner.SchemeName
ELEMENT ElementNameElementType
MASTER DatabaseName ON "HostName"
SUBSCRIBER SubDatabase1 ON "HostName",
SubDatabase2 ON "HostName"
ReturnServiceAttribute;

RETURN RECEIPT

TimesTen provides an optional return receipt service to loosely couple or synchronize your application with the replication mechanism.

- In an active standby pair, you can specify the RETURN RECEIPT clause to enable the return receipt service for the standby database. With return receipt enabled, when your application commits a transaction for an element on the active database, the application remains blocked until the standby acknowledges receipt of the transaction update.

- In a classic replication scheme, you can specify the RETURN RECEIPT clause to enable the return receipt service for the subscriber database. With return receipt enabled, when your application commits a transaction for an element on the master database, the application remains blocked until the subscriber acknowledges receipt of the transaction update. If the master is replicating the element to multiple subscribers, the application remains blocked until all of the subscribers have acknowledged receipt of the transaction update.

Note:
You can also configure the replication agent to disable the return receipt service after a specific number of timeouts. See "Setting the return service timeout period" for details on timeouts.

If the standby or subscriber is unable to acknowledge receipt of the transaction within a configurable timeout period, your application receives a tt_ErrRepReturnFailed (8170) warning on its commit request.

Example 4-3 Defining RETURN RECEIPT for an active standby pair

The following example creates an active standby pair where master1 is the active database, master2 is the standby database. The standby database is enabled with the return receipt service.

Command> CREATE ACTIVE STANDBY PAIR
> master1,
> master2
> RETURN RECEIPT;

Example 4-4 Defining RETURN RECEIPT for a classic replication scheme

To confirm that all transactions committed on the tab table in the master database (masterds) are received by the subscriber (subscriberds), the element description (e) might look like the following:

NOTE: For more examples of classic replication schemes that use return receipt services, see Example 9-5 and Example 9-6.

ELEMENT e TABLE tab
MASTER masterds ON "system1"
SUBSCRIBER subscriberds ON "system2"
RETURN RECEIPT

RETURN RECEIPT BY REQUEST

RETURN RECEIPT enables notification of receipt for all transactions. You can use the RETURN RECEIPT BY REQUEST clause to enable an acknowledgement receipt notification only for specific transactions identified by your application.

If you specify RETURN RECEIPT BY REQUEST, you must use the ttRepSyncSet built-in procedure on the active or master database to enable the return receipt service for a transaction. The call to enable the return receipt service must be part of the transaction (autocommit must be off).

If the standby or subscriber database is unable to acknowledge receipt of the transaction update within a configurable timeout period, the application receives a tt_ErrRepReturnFailed (8170) warning on its commit request. See "Setting the return service timeout period" for more information on the return service timeout period.

Example 4-5 RETURN RECEIPT BY REQUEST for an active standby pair

The following example creates an active standby pair where master1 is the active database and master2 is the standby database. The standby database is enabled with the return receipt service.

Command> CREATE ACTIVE STANDBY PAIR
> master1,
> master2
> RETURN RECEIPT BY REQUEST;

Example 4-6 RETURN RECEIPT BY REQUEST for a classic replication scheme

To enable confirmation that specific transactions committed on the tab table in the master database (masterds) are received by the subscriber (subscriberds), the element description (e) might look like:

ELEMENT e TABLE tab
MASTER masterds ON "system1"
SUBSCRIBER subscriberds ON "system2"
RETURN RECEIPT BY REQUEST

Example 4-7 Using ttRepSyncSet to request the return services

Before committing a transaction that requires an acknowledgement return receipt, call ttRepSyncSet. The following example sets the request for a return receipt with the first column set to 0x01 with a timeout value of 45 seconds in column two.

Command> autocommit off;
Command> CALL ttRepSyncSet(0x01, 45, 1);

You can use ttRepSyncGet to check if a return service is enabled and obtain the timeout value. The following demonstrates that the values that were previously set with the ttRepSyncSet built-in procedure.

Command> CALL ttRepSyncGet;
< 01, 45, 1 >
1 row found.

For more information, see "ttRepSyncSet" and "ttRepSyncGet" in the Oracle TimesTen In-Memory Database Reference.

RETURN TWOSAFE

TimesTen provides a return twosafe service to fully synchronize your application with the replication mechanism. The return twosafe service ensures that each replicated transaction is committed on the standby database before it is committed on the active database. If replication is unable to verify the transaction has been committed on the standby or subscriber, it returns notification of the error. Upon receiving an error, the application can either take a unique action or fall back on preconfigured actions, depending on the type of failure.

Note:
When replication is configured with RETURN TWOSAFE, you must disable autocommit mode.

To enable the return twosafe service for the subscriber, specify the RETURN TWOSAFE attribute in the CREATE ACTIVE STANDBY PAIR, ALTER ACTIVE STANDBY PAIR, CREATE REPLICATION, or ALTER REPLICATION statements.

- When using an active standby pair, a transaction that contains operations that are replicated with RETURN TWOSAFE cannot have a PassThrough setting greater than 0. If PassThrough is greater than 0, an error is returned and the transaction must be rolled back.

- When using a classic replication scheme, the return twosafe service is intended to be used in replication schemes where two databases must stay synchronized. One database has an active role, while the other database has a standby role but must be ready to assume an active role at any moment. Use return twosafe with a bidirectional replication scheme with exactly two databases.
When the application commits a transaction on the master database, the application remains blocked until the subscriber acknowledges it has successfully committed the transaction. Initiating identical updates or deletes on both databases can lead to deadlocks in commits that can be resolved only by stopping the processes.

If the standby or subscriber is unable to acknowledge commit of the transaction update within a configurable timeout period, the application receives a tt_ErrRepReturnFailed (8170) warning on its commit request. See "Setting the return service timeout period" for more information on the return service timeout period.

Example 4-8 RETURN TWOSAFE with an active standby pair

The following example creates an active standby pair where master1 is the active database, master2 is the standby database. The standby database is enabled with the return twosafe service.

Command> CREATE ACTIVE STANDBY PAIR
> master1,
> master2
> RETURN TWOSAFE;

Example 4-9 RETURN TWOSAFE with a classic replication scheme

To confirm all transactions committed on the master database (databaseA) are also committed by the subscriber (databaseB), the element description (a) might look like the following:

ELEMENT a DATASTORE
MASTER databaseA ON "system1"
SUBSCRIBER databaseB ON "system2"
RETURN TWOSAFE

The entire CREATE REPLICATION statement that specifies both databaseA and databaseB in a bidirectional configuration with RETURN TWOSAFE might look like the following:

CREATE REPLICATION bidirect
ELEMENT a DATASTORE
MASTER databaseA ON "system1"
SUBSCRIBER databaseB ON "system2"
RETURN TWOSAFE
ELEMENT b DATASTORE
MASTER databaseB ON "system2"
SUBSCRIBER databaseA ON "system1"
RETURN TWOSAFE;

RETURN TWOSAFE BY REQUEST

RETURN TWOSAFE enables notification of commit on the standby database for all transactions. You can use the RETURN TWOSAFE BY REQUEST clause to enable notification of a commit on the standby only for specific transactions identified by your application.

If you specify RETURN TWOSAFE BY REQUEST for a standby or subscriber database, you must use the ttRepSyncSet built-in procedure on the active or master database to enable the return twosafe service for a transaction. The call to enable the return twosafe service must be part of the transaction (autocommit must be off).

The ALTER TABLE statement cannot be used to alter a replicated table that is part of a RETURN TWOSAFE BY REQUEST transaction. If DDLCommitBehavior=0 (the default), the ALTER TABLE operation succeeds because a commit is performed before the ALTER TABLE operation, resulting in the ALTER TABLE operation executing in a new transaction which is not part of the RETURN TWOSAFE BY REQUEST transaction. If DDLCommitBehavior=1, the ALTER TABLE operation results in error 8051.

Note:
See "Setting the return service timeout period" for more information on setting the return service timeout period.

If the standby or subscriber is unable to acknowledge commit of the transaction within the timeout period, the application receives a tt_ErrRepReturnFailed (8170) warning on its commit request. The application can then chose how to handle the timeout. See "Setting the return service timeout period".

When using an active standby pair, a transaction that contains operations that are replicated with RETURN TWOSAFE cannot have a PassThrough setting greater than 0. If PassThrough is greater than 0, an error is returned and the transaction must be rolled back.

Example 4-10 RETURN TWOSAFE BY REQUST for an active standby pair

The following example creates an active standby pair where master1 is the active database, master2 is the standby database. The standby database is enabled with the return twosafe by request service.

Command> CREATE ACTIVE STANDBY PAIR
> master1,
> master2
> RETURN TWOSAFE BY REQUEST;

Before calling commit for a transaction that requires confirmation of commit on the subscriber, call the ttRepSyncSet built-in procedure to request the return service, set the timeout period to 45 seconds, and specify no action (1) in the event of a timeout error:

Command> CALL ttRepSyncSet(0x01, 45, 1);

You can use the ttRepSyncGet built-in procedure to check if a return service is enabled and obtain the timeout value.

Command> CALL ttRepSyncGet();
< 01, 45, 1>
1 row found.

Example 4-11 RETURN TWOSAFE BY REQUEST for a classic replication scheme

To enable confirmation that specific transactions committed on the master database (databaseA) are also committed by the subscriber (databaseB), the element description (a) might look like:

ELEMENT a DATASTORE
MASTER databaseA ON "system1"
SUBSCRIBER databaseB ON "system2"
RETURN TWOSAFE BY REQUEST;

Before calling commit for a transaction that requires confirmation of commit on the subscriber, call the ttRepSyncSet built-in procedure to request the return service, set the timeout period to 45 seconds, and specify no action (1) in the event of a timeout error:

Command> CALL ttRepSyncSet(0x01, 45, 1);

You can use the ttRepSyncGet built-in procedure to check if a return service is enabled and obtain the timeout value.

Command> CALL ttRepSyncGet();
< 01, 45, 1>
1 row found.

NO RETURN

You can use the NO RETURN clause to explicitly disable either the return receipt or return twosafe services, depending on which one you have enabled. NO RETURN is the default condition. This attribute is typically used only when altering a replication scheme to remove a previously defined return service in the ALTER ACTIVE STANDBY PAIR or ALTER REPLICATION statements. See Example 10-13.

Setting STORE attributes

The STORE attributes clause in the CREATE ACTIVE STANDBY PAIR, ALTER ACTIVE STANDBY PAIR, CREATE REPLICATION, and ALTER REPLICATION statements are used to set optional behavior for return services, compression, timeouts, durable commit behavior, and table definition checking. For a classic replication scheme, you can also define conflict reporting at the table level.

Note:
See "CREATE ACTIVE STANDBY PAIR" and "CREATE REPLICATION" in the Oracle TimesTen In-Memory Database SQL Reference for the full description and syntax for the STORE attributes.

When using classic replication schemes, the FAILTHRESHOLD and TIMEOUT attributes can be unique to a specific classic replication scheme definition. This means these attribute settings can vary if you have applied different classic replication scheme definitions to your replicated databases. This is not true for any of the other attributes, which must be the same across all classic replication scheme definitions. For example, setting the PORT attribute for one classic replication scheme sets it for all classic replication schemes. For an example classic replication scheme that uses a STORE clause to set the FAILTHRESHOLD attribute, see Example 9-5.

Note:
If you are using ALTER ACTIVE STANDBY PAIR to change any of the STORE attributes, you must follow the steps described in "Making other changes to an active standby pair".

The following sections describe some of the STORE attributes:

- Setting the return service timeout period

- Column definition options for replicated tables

- Compressing replicated traffic

- Port assignments

- Setting wait timeout for response from remote replication agents

- Setting the transaction log failure threshold

- Suspending or resuming classic replication in response to conflicts

Setting the return service timeout period

The following describes how a timeout can occur in a replication scheme configured with one of the return services described in "Using a return service".

- In an active standby pair replication scheme, a timeout occurs if the standby database is unable to send an acknowledgement back to the active database within the time period specified by RETURN WAIT TIME.
If the standby database is unable to acknowledge the transaction update from the active database within the timeout period, the application receives an errRepReturnFailed warning on its commit request.

- In a classic replication scheme, a timeout occurs if any of the subscribers are unable to send an acknowledgement back to the master within the time period specified by RETURN WAIT TIME.
The replication state could be set to stop by a user or by the master replication agent in the event of a subscriber failure. A subscriber may be unable to acknowledge a transaction that makes use of a return service and may time out with respect to the master.

If any of the subscribers are unable to acknowledge the transaction update within the timeout period, the application receives an errRepReturnFailed warning on its commit request.

A return service may time out because of a replication failure or because replication is so far behind that the return service transaction times out before it is replicated. However, unless there is a simultaneous replication failure, failure to obtain a return service confirmation from the standby or subscriber does not necessarily mean the transaction has not been or will not be replicated.

The default return service timeout period is 10 seconds. You can specify a different return service timeout period by either:

- Specifying the RETURN WAIT TIME in the CREATE ACTIVE STANDBY PAIR, ALTER ACTIVE STANDBY PAIR, CREATE REPLICATION, or ALTER REPLICATION statements.
The RETURN WAIT TIME attribute specifies the number of seconds to wait for a return service acknowledgement. A value of 0 means that there is no waiting.

The following example alters an active database (master1) of an active standby pair to set a return service wait time of 25 seconds:

Command> ALTER ACTIVE STANDBY PAIR
> ALTER STORE master1 SET RETURN WAIT TIME 25;

- Specifying a different return service timeout period programmatically by calling the ttRepSyncSet built-in procedure on either the active database (in an active standby pair) or the master database (in a classic replication scheme) with a new timeout value for the returnWait parameter.
The following example demonstrates how to set the return service wait time to 25 seconds using ttRepSyncSet:

Command> CALL ttRepSyncSet (0x01, 25, 1);

Once the timeout is set, the timeout period applies to all subsequent return service transactions until you either reset the timeout period or terminate the application session. For a classic replication scheme, the timeout setting applies to all return services for all subscribers.

Note:
You can set other STORE attributes to establish policies that automatically disable return service blocking in the event of excessive timeouts and re-enable return service blocking when conditions improve. See "Managing return service timeout errors and replication state changes".

Example 4-12 Setting the timeout period for both databases in bidirectional (classic) replication scheme

To set the timeout period to 30 seconds for both bidirectionally replicated databases, databaseA and databaseB, in the bidirect replication scheme, the CREATE REPLICATION statement might look like the following:

CREATE REPLICATION bidirect
ELEMENT a DATASTORE
MASTER databaseA ON "system1"
SUBSCRIBER databaseB ON "system2"
RETURN TWOSAFE
ELEMENT b DATASTORE
MASTER databaseB ON "system2"
SUBSCRIBER databaseA ON "system1"
RETURN TWOSAFE
STORE databaseA RETURN WAIT TIME 30
STORE databaseB RETURN WAIT TIME 30;

Example 4-13 Resetting the timeout period

Use the ttRepSyncSet built-in procedure to reset the timeout period to 45 seconds. To avoid resetting the requestReturn and localAction values, specify NULL:

Command> CALL ttRepSyncSet(NULL, 45, NULL);

Managing return service timeout errors and replication state changes

The following sections describe how to detect and respond to timeouts on return service transactions:

Note:
One response to a timeout is to disable the return service. You can determine if the return service is enabled or disabled with either the ttRepSyncSubscriberStatus built-in procedure or the ttRepReturnTransitionTrap SNMP trap. For more information, see "Determine if return service is disabled".

- Disabling return service blocking manually

- Establishing return service failure/recovery policies

Disabling return service blocking manually

You may want to react if replication is stopped or return service timeout failures begin to adversely impact the performance of your replicated system. Your "tolerance threshold" for return service timeouts may depend on the historical frequency of timeouts and the performance/availability equation for your particular application, both of which should be factored into your response to the problem.

When using the return receipt service, you can manually respond by:

- Using the ALTER ACTIVE STANDBY PAIR or ALTER REPLICATION statements to disable return receipt blocking. If you decide to disable return receipt blocking, your decision to re-enable it depends on your confidence level that the return receipt transaction is no longer likely to time out.
The following example uses the ALTER ACTIVE STANDBY PAIR statement to disable return receipt after 10 failures:

Command> ALTER ACTIVE STANDBY PAIR
> ALTER STORE master1 SET DISABLE RETURN ALL 10;

- Calling the ttDurableCommit built-in procedure to durably commit transactions on the active or master database that you can no longer verify as being received by the standby or subscriber database.

Establishing return service failure/recovery policies

An alternative to manually responding to return service timeout failures is to establish return service failure and recovery policies in the replication scheme. These policies direct the replication agents to detect changes to the replication state and to keep track of return service timeouts and then automatically respond in a predefined manner.

The following attributes in the CREATE ACTIVE STANDBY PAIR, ALTER ACTIVE STANDBY PAIR, CREATE REPLICATION, or ALTER REPLICATION statements set the failure and recovery policies when using a RETURN RECEIPT or RETURN TWOSAFE service:

- RETURN SERVICES {ON | OFF} WHEN [REPLICATION] STOPPED

- DISABLE RETURN

- RESUME RETURN

- DURABLE COMMIT

- LOCAL COMMIT ACTION

The policies set by these attributes are applicable until changed. Except for DURABLE COMMIT, the replication agent must be running to enforce these policies.

RETURN SERVICES {ON | OFF} WHEN [REPLICATION] STOPPED

The RETURN SERVICES {ON | OFF} WHEN [REPLICATION] STOPPED attribute determines whether a return receipt or return twosafe service continues to be enabled or is disabled when replication is stopped.

- In an active standby pair, "stopped" means either the active replication agent is stopped (for example, by ttAdmin -repStop active) or the replication state of the standby database is set to stop or pause with respect to the active database (for example, by ttRepAdmin -state stop standby). A failed standby database that has exceeded the specified FAILTHRESHOLD value is set to the failed state, but is eventually set to the stop state by the replication agent on the active database.

- In a classic replication scheme, "stopped" means either the master replication agent is stopped (for example, by ttAdmin -repStop master) or the replication state of the subscriber database is set to stop or pause with respect to the master database (for example, by ttRepAdmin -state stop subscriber). A failed subscriber that has exceeded the specified FAILTHRESHOLD value is set to the failed state, but is eventually set to the stop state by the master replication agent.

Note:
A standby or subscriber database may become unavailable for a period of time that exceeds the timeout period specified by RETURN WAIT TIME, yet still be considered by the master replication agent to be in the start state. Failure policies related to timeouts are set by the DISABLE RETURN attribute.

- RETURN SERVICES OFF WHEN REPLICATION STOPPED disables the return service when replication is stopped and is the default when using the RETURN RECEIPT service.

- RETURN SERVICES ON WHEN REPLICATION STOPPED enables the return service to continue to be enabled when replication is stopped and is the default when using the RETURN TWOSAFE service.

Example 4-14 RETURN SERVICES ON WHEN REPLICATION STOPPED for an active standby pair

The following example creates an active standby pair with RETURN TWOSAFE return service and defines that the return service is to be disabled when replication is stopped (which is opposite of the default).

Command> CREATE ACTIVE STANDBY PAIR
> master1,
> master2
> RETURN TWOSAFE
> STORE master2 RETURN SERVICES OFF WHEN REPLICATION STOPPED;

While the application is committing updates to the active database master1, ttRepAdmin is used to set the standby database master2 to the stop state:

ttRepAdmin -receiver -name master2 -state stop master1

The application continues to wait for return receipt acknowledgements from master2 until the replication state is reset to start and it receives the acknowledgment:

ttRepAdmin -receiver -name master2 -state start master1

Example 4-15 RETURN SERVICES ON WHEN REPLICATION STOPPED for a classic replication scheme

Configure the CREATE REPLICATION statement to replicate updates from the masterds database to the subscriber1 database. The CREATE REPLICATION statement specifies the use of RETURN RECEIPT and RETURN SERVICES ON WHEN REPLICATION STOPPED.

CREATE REPLICATION myscheme
ELEMENT e TABLE tab
MASTER masterds ON "server1"
SUBSCRIBER subscriber1 ON "server2"
RETURN RECEIPT
STORE masterds ON "server1"
RETURN SERVICES ON WHEN REPLICATION STOPPED;

While the application is committing updates to the master, ttRepAdmin is used to set subscriber1 to the stop state:

ttRepAdmin -receiver -name subscriber1 -state stop masterds

The application continues to wait for return receipt acknowledgements from subscriber1 until the replication state is reset to start and it receives the acknowledgment:

ttRepAdmin -receiver -name subscriber1 -state start masterds

DISABLE RETURN

When a DISABLE RETURN value is set, the database keeps track of the number of return receipt or return twosafe transactions that have exceeded the timeout period set by RETURN WAIT TIME. If the number of timeouts exceeds the maximum value set by DISABLE RETURN, the application reverts to a default replication cycle in which it no longer waits for the standby or subscriber to acknowledge the replicated updates.

When return service blocking is disabled, the applications on the active or master database no longer block execution while waiting to receive acknowledgements from the standby or subscribers that they received or committed the replicated updates. Transactions are still replicated to the standby or subscriber, whether the return service is enabled or disabled. When the return service is disabled, the transactions are sent in asynchronous mode; the active or master database continues to listen for an acknowledgement of each batch of replicated updates from standby or subscriber databases.

Configure DISABLE RETURN as follows:

- For an active standby pair, specifying SUBSCRIBER is the same as specifying ALL. Both settings refer to the standby database.

- For a classic replication scheme, you can set DISABLE RETURN SUBSCRIBER to establish a failure policy to disable return service blocking for only those subscribers that have timed out, or DISABLE RETURN ALL to establish a policy to disable return service blocking for all subscribers.

Note:
You can use the ttRepSyncSubscriberStatus built-in procedure or the ttRepReturnTransitionTrap SNMP trap to determine whether the standby database or a particular subscriber has been disabled by the DISABLE RETURN failure policy.

The DISABLE RETURN failure policy is only enabled when the replication agent is running. If DISABLE RETURN is specified without RESUME RETURN, the return services remain off until the replication agent for the database has been restarted.

- For an active standby pair, you can cancel this failure policy by stopping the replication agent and specifying DISABLE RETURN with a zero value for NumFailures.

- For a classic replication scheme, you can cancel this failure policy by stopping the replication agent and specifying either DISABLE RETURN SUBSCRIBER or DISABLE RETURN ALL with a zero value for NumFailures.
DISABLE RETURN maintains a cumulative timeout count for each subscriber. If there are multiple subscribers and you set DISABLE RETURN SUBSCRIBER, the replication agent disables return service blocking for the first subscriber that reaches the timeout threshold. If one of the other subscribers later reaches the timeout threshold, the replication agent disables return service blocking for that subscriber also.

The count of timeouts to trigger the failure policy is reset either when you restart the replication agent, when you set the DISABLE RETURN value to 0, or when return service blocking is re-enabled by RESUME RETURN.

Example 4-16 DISABLE RETURN for an active standby pair

Configure the CREATE ACTIVE STANDBY PAIR statement to replicate updates from the active database master1 to the standby database master2. The CREATE ACTIVE STANDBY PAIR statement specifies the use of RETURN RECEIPT and DISABLE RETURN ALL with a NumFailures value of 5. The RETURN WAIT TIME is set to 30 seconds.

CREATE ACTIVE STANDBY PAIR
master1,
master2
RETURN RECEIPT
STORE master1
DISABLE RETURN ALL 5
RETURN WAIT TIME 30;

While the application is committing updates to the active database, the standby database (master2) experiences problems and fails to acknowledge a replicated transaction update. The application is blocked for 30 seconds after which it commits its next update to the active database master1. Over the course of the application session, this commit/timeout cycle repeats 4 more times until DISABLE RETURN disables return receipt blocking for master2.

For another example that sets the DISABLE RETURN attribute for an active standby pair, see Example 4-18.

Example 4-17 DISABLE RETURN SUBSCRIBER for a classic replication scheme

Configure the CREATE REPLICATION statement to replicate updates from the masterds master database to the subscriber databases: subscriber1 and subscriber2. The CREATE REPLICATION statement specifies the use of RETURN RECEIPT and DISABLE RETURN SUBSCRIBER with a NumFailures value of 5. The RETURN WAIT TIME is set to 30 seconds.

CREATE REPLICATION myscheme
ELEMENT e TABLE tab
MASTER masterds ON "server1"
SUBSCRIBER subscriber1 ON "server2",
subscriber2 ON "server3"
RETURN RECEIPT
STORE masterds ON "server1"
DISABLE RETURN SUBSCRIBER 5
RETURN WAIT TIME 30;

While the application is committing updates to the master, subscriber1 experiences problems and fails to acknowledge a replicated transaction update. The application is blocked for 30 seconds after which it commits its next update to the master database masterds. Over the course of the application session, this commit/timeout cycle repeats 4 more times until DISABLE RETURN disables return receipt blocking for subscriber1. The application continues to wait for return-receipt acknowledgements from subscriber2, but not from subscriber1.

For another example that sets the DISABLE RETURN attribute for a classic replication scheme, see Example 4-19.

RESUME RETURN

If DISABLE RETURN has disabled return service blocking, the RESUME RETURN attribute sets the policy for re-enabling the return service. You can establish a return service recovery policy by setting the RESUME RETURN attribute and specifying a resume latency value.

If return service blocking has been disabled for the standby or subscriber database and a latency time has been defined for RESUME RETURN, the following occurs:

- The applications on the active or master database no longer block execution while waiting to receive acknowledgements from the standby or subscribers. Transactions continue to be replicated to the standby or subscriber in asynchronous mode. The active or master databases continue to listen for an acknowledgement of each batch of replicated updates from standby or subscriber databases.

- If the return service blocking is disabled, RESUME RETURN evaluates the commit-to-acknowledge time for the last transaction to see if the latency is less than the latency limit configured by the RESUME RETURN. If the commit-to-acknowledge time latency is less than the latency limit set by RESUME RETURN, TimesTen re-enables the return receipt or return twosafe services.

Note:
The commit-to-acknowledge time latency is the time elapsed between when the application issues a commit and when the active or master database receives acknowledgement from the standby or subscriber.
TimesTen evaluates the latency of the last acknowledged transaction before the current transaction is replicated to the standby or subscriber. The return service is re-enabled before the sending of the current transaction after evaluating the latency from the last transaction.

The RESUME RETURN policy is enabled only when the replication agent is running. You can cancel a return receipt resume policy by stopping the replication agent and then using ALTER ACTIVE STANDBY PAIR or ALTER REPLICATION statements to set RESUME RETURN to zero.

Example 4-18 RESUME RETURN for an active standby pair

If return receipt blocking has been disabled for master2 and if RESUME RETURN is set to 8 milliseconds, then return receipt blocking is re-enabled for master2 the instant the active receives an acknowledgement of the update from the standby, as long as the acknowledgement is received within the specified latency 8 milliseconds from when it was committed by the application on the active database.

Command> CREATE ACTIVE STANDBY PAIR
> master1,
> master2
> RETURN RECEIPT
> STORE master1
> DISABLE RETURN ALL 5
> RESUME RETURN 8;

Example 4-19 RESUME RETURN for a classic replication scheme

If return receipt blocking has been disabled for subscriber1 and if RESUME RETURN is set to 8 milliseconds, then return receipt blocking is re-enabled for subscriber1 the instant the master receives an acknowledgement of the update from the subscriber, as long as the acknowledgement is received within the specified latency 8 milliseconds from when it was committed by the application on the master database.

CREATE REPLICATION myscheme
ELEMENT e TABLE ttuser.tab
MASTER masterds ON "server1"
SUBSCRIBER subscriber1 ON "server2",
subscriber2 ON "server3"
RETURN RECEIPT
STORE masterds ON "server1"
DISABLE RETURN SUBSCRIBER 5
RESUME RETURN 8;

DURABLE COMMIT

You can set the DURABLE COMMIT attribute to specify the durable commit policy for applications that have return service blocking disabled by DISABLE RETURN. When DURABLE COMMIT is set to ON, it overrides the DurableCommits general connection attribute on the active or master database and forces durable commits for those transactions that have had return service blocking disabled.

In addition, when DURABLE COMMIT is set to ON, durable commits are issued when return service blocking is disabled regardless of whether the replication agent is running or stopped. They are also issued when the ttRepStateSave built-in procedure has marked the standby or subscriber database as failed.

For a classic replication scheme, DURABLE COMMIT is useful if you have only one subscriber. However, if you are replicating the same data to two subscribers and you disable return service blocking to one subscriber, then you achieve better performance if you rely on the other subscriber than you would if you enable durable commits.

Example 4-20 DURABLE COMMIT ON with an active standby pair

Set DURABLE COMMIT ON when establishing a DISABLE RETURN ALL policy to disable return-receipt blocking for all subscribers. If return-receipt blocking is disabled, commits are durably committed to disk to provide redundancy.

Command> CREATE ACTIVE STANDBY PAIR
> master1,
> master2
> RETURN RECEIPT
> STORE master1
> DISABLE RETURN ALL 5
> DURABLE COMMIT ON
> RESUME RETURN 8;

Example 4-21 DURABLE COMMIT ON with a classic replication scheme

Set DURABLE COMMIT ON when establishing a DISABLE RETURN ALL policy to disable return-receipt blocking for all subscribers. If return-receipt blocking is disabled, commits are durably committed to disk to provide redundancy.

CREATE REPLICATION myscheme
ELEMENT e TABLE tab
MASTER masterds ON "server1"
SUBSCRIBER subscriber ON "server2",
subscriber2 ON "server3"
RETURN RECEIPT
STORE masterds ON "server1"
DISABLE RETURN ALL 5
DURABLE COMMIT ON
RESUME RETURN 8;

LOCAL COMMIT ACTION

When you are using the return twosafe service, you can specify how the active or master replication agent responds to timeouts by setting LOCAL COMMIT ACTION. You can override this setting for specific transactions with the localAction parameter of the ttRepSyncSet built-in procedure.

The possible actions upon receiving a timeout during replication of a twosafe transaction are:

- COMMIT - On timeout, the commit function attempts to perform a commit to end the transaction locally. No more operations are possible on the same transaction.

- NO ACTION - On timeout, the commit function returns to the application, leaving the transaction in the same state it was in when it entered the commit call, with the exception that the application is not able to update any replicated tables. The application can reissue the commit. This is the default.

If the call returns with an error, you can use the ttRepXactStatus procedure described in "Check the status of return service transactions" to check the status of the transaction. Depending on the error, your application can choose to:

- Reissue the commit call - This repeats the entire return twosafe replication cycle, so that the commit call returns when the success or failure of the replicated commit on the subscriber is known or if the timeout period expires.

- Roll back the transaction - If the call returns with an error related to applying the transaction on the standby or subscriber, such as primary key lookup failure, you can roll back the transaction on the active or master database.

Column definition options for replicated tables

The definition for the columns of replicated tables participating in the replication scheme do not necessarily need to be identical.

- If the TABLE DEFINITION CHECKING value is set to EXACT, the column definitions must be identical on the active and standby databases. This attribute enables replication of tables that are identical in their physical structure.

- If the TABLE DEFINITION CHECKING value is set to RELAXED (the default), the column definitions of the replicated tables do not need to be identical. When using RELAXED, the replicated tables must have the same key definition, number of columns, column names, and column data types.
Table definition checking occurs on the standby database. Setting this attribute to RELAXED for both active and standby databases has the same effect as setting it for only the standby database.

Note:
For more details on TABLE DEFINITION CHECKING, see "CREATE ACTIVE STANDBY PAIR" or "CREATE REPLICATION" in the Oracle TimesTen In-Memory Database SQL Reference.

The TABLE DEFINITION CHECKING RELAXED attribute does not require that the physical structure of the table be identical on both master databases. For example, if tables have columns in a different order or have a different number of partitions, the data can still be replicated when using the RELAXED attribute. Thus, if you are altering your table by adding or dropping columns, you should use the RELAXED attribute. As noted in "ALTER TABLE" in the Oracle TimesTen In-Memory Database SQL Reference, adding columns when altering a table creates additional partitions. Dropping columns does not automatically free up the space. We recommend that any DML statement that alters the table should be executed on the master and then replicated to any standby database and subscribers.

The RELAXED setting can result in slightly slower performance if it is compensating for a different physical structure. If the tables are identical in physical structure, then there is no performance impact. You can eliminate any performance issues (caused by a different physical structure, additional partitions, or extraneous space) by using the ttMigrate -r -relaxedUpgrade (only valid on databases where the table definition checking is set to RELAXED) to coalesce all additional partitions of a table into a single partition and eliminate extraneous space caused by dropped columns. If you perform this on all databases involved in the replication scheme, the resulting physical structure is identical resulting in the best performance potential.

Note:
See Example 4-18 and "Check partition counts for the tables" in Oracle TimesTen In-Memory Database Troubleshooting Guide for information on how to check the partitions in use for each table.
For performance considerations of both the EXACT and RELAXED attributes for TABLE DEFINITION CHECKING, see "Performance considerations when altering tables that are replicated".

To ensure that table definition checking is set to RELAXED, stop the replication agent on the active or master database and then execute an ALTER ACTIVE STANDBY PAIR or ALTER REPLICATION statement to set the table definition checking to RELAXED. Finally, use the ttRepAdmin -duplicate command to roll out these changes to the standby database and any subscribers. For more information, see "ALTER ACTIVE STANDBY PAIR" and "ALTER REPLICATION" in the Oracle TimesTen In-Memory Database SQL Reference.

The following sections provide examples for setting the table definition checking to relaxed:

- Examples for an active standby pair replicating tables with table definition checking set to relaxed

- Examples for classic replication scheme with table definition checking set to relaxed

Examples for an active standby pair replicating tables with table definition checking set to relaxed

The following examples demonstrate the effect of setting the TABLE DEFINITION CHECKING attribute to either EXACT or RELAXED in an active standby pair replication scheme.

Example 4-22 Replicating tables that are identical in an active standby pair

Create table t1 in master1 database:

CREATE TABLE t1 (a INT PRIMARY KEY, b INT, c INT);

Create an active standby pair replication scheme. Set TABLE DEFINITION CHECKING to EXACT for the master2 standby database.

Command> CREATE ACTIVE STANDBY PAIR master1, master2
> STORE master2 TABLE DEFINITION CHECKING EXACT;

Perform the rest of the steps to duplicate the active database to the standby database, start the replication agents on both databases, and set the state of the active database (as described in Chapter 2, "Getting Started".

Insert a row into t1 on master1.

Command> INSERT INTO t1 VALUES (4,5,6);
1 row inserted.

Verify the results on t1 on master2.

Command> SELECT * FROM t1;
< 4, 5, 6>
1 row found.

Example 4-23 Altering the table definition checking to relaxed in an active standby pair

You can alter the table definition checking for the active standby pair replication scheme to be relaxed. First, stop the replication agent on the active database before altering the active database. The following alters the dsn1 active database so the table definition checking is set to relaxed:

ALTER ACTIVE STANDBY PAIR
ALTER STORE master1 SET TABLE DEFINITION CHECKING RELAXED;

After execution completes, use duplicate to roll out the changes to the standby database. Lastly, use duplicate to roll out the changes to any subscribers.

Examples for classic replication scheme with table definition checking set to relaxed

The following examples demonstrate the effect of setting the TABLE DEFINITION CHECKING attribute to either EXACT or RELAXED in a classic replication scheme.

Example 4-24 Replicating tables that are identical in a classic replication scheme

Create table t1 in dsn1 database:

CREATE TABLE ttuser.t1 (a INT PRIMARY KEY, b INT, c INT);

Create ttuser.t1 table in the dsn2 database exactly the same as in the dsn1 database.

Create replication scheme ttuser.rep1. Set TABLE DEFINITION CHECKING to EXACT for the subscriber, dsn2.

CREATE REPLICATION ttuser.rep1
ELEMENT e1 TABLE ttuser.t1
MASTER dsn1
SUBSCRIBER dsn2
STORE dsn2 TABLE DEFINITION CHECKING EXACT;

Start the replication agent for both databases. Insert a row into ttuser.t1 on dsn1.

Command> INSERT INTO ttuser.t1 VALUES (4,5,6);
1 row inserted.

Verify the results on ttuser.t1 on dsn2.

Command> SELECT * FROM ttuser.t1;
< 4, 5, 6>
1 row found.

Example 4-25 Replicating tables with columns in different positions in a classic replication scheme

Create table t1 in dsn1 database:

CREATE TABLE ttuser.t1 (a INT PRIMARY KEY, b INT, c INT);

Create table ttuser.t1 in dsn2 database with the columns in a different order than the columns in ttuser.t1 in dsn1 database. Note that the column names and data types are the same in both tables and a is the primary key in both tables.

CREATE TABLE ttuser.t1 (c INT, a INT PRIMARY KEY, b INT);

Create replication scheme ttuser.rep1. Set TABLE DEFINITION CHECKING to RELAXED for the subscriber, dsn2.

CREATE REPLICATION ttuser.rep1
ELEMENT e1 TABLE ttuser.t1
MASTER dsn1
SUBSCRIBER dsn2
STORE dsn2 TABLE DEFINITION CHECKING RELAXED;

Start the replication agent for both databases. Insert a row into ttuser.t1 on dsn1.

Command> INSERT INTO ttuser.t1 VALUES (4,5,6);
1 row inserted.

Verify the results on ttuser.t1 on dsn2.

Command> SELECT * FROM ttuser.t1;
< 5, 6, 4 >
1 row found.

Example 4-26 Replicating tables with a different number of partitions in a classic replication scheme

When you alter a table to add columns, it increases the number of partitions in the table, even if you subsequently drop the new columns. You can use the RELAXED setting for TABLE DEFINITION CHECKING to replicate tables that have different number of partitions.

Create table ttuser.t3 on dsn1 with two columns.

CREATE TABLE ttuser.t3 (a INT PRIMARY KEY, b INT);

Create table ttuser.t3 on dsn2 with one column that is the primary key.

CREATE TABLE ttuser.t3 (a INT PRIMARY KEY);

Add a column to the table on dsn2. This increases the number of partitions to two, while the table on dsn1 has one partition.

ALTER TABLE ttuser.t3 ADD COLUMN b INT;

Create the replication scheme on both databases.

CREATE REPLICATION reppart
ELEMENT e2 TABLE ttuser.t3
MASTER dsn1
SUBSCRIBER dsn2
STORE dsn2 TABLE DEFINITION CHECKING RELAXED;

Start the replication agent for both databases. Insert a row into ttuser.t3 on dsn1.

Command> INSERT INTO ttuser.t3 VALUES (1,2);
1 row inserted.

Verify the results in ttuser.t3 on dsn2.

Command> SELECT * FROM ttuser.t3;
< 1, 2 >
1 row found.

Example 4-27 Altering the table definition checking to relaxed in a classic replication scheme

You can alter the table definition checking for a classic replication scheme to be relaxed. First, stop the replication agent on the master database before altering the replication scheme on it. The following alters the dsn1 master database so the table definition checking is set to relaxed:

ALTER REPLICATION reppart
ALTER STORE dsn1 SET TABLE DEFINITION CHECKING RELAXED;

After execution completes, use duplicate to roll out the changes to the standby master. Lastly, use duplicate to roll out the changes to any subscribers.

Compressing replicated traffic

If you are replicating over a low-bandwidth network, or if you are replicating massive amounts of data, you can set the COMPRESS TRAFFIC attribute to reduce the amount of bandwidth required for replication. The COMPRESS TRAFFIC attribute compresses the replicated data from the database specified by the STORE parameter in the CREATE ACTIVE STANDBY PAIR, ALTER ACTIVE STANDBY PAIR, CREATE REPLICATION or ALTER REPLICATION statements. TimesTen does not compress traffic from other databases.

Though the compression algorithm is optimized for speed, enabling the COMPRESS TRAFFIC attribute affects replication throughput and latency.

Example 4-28 Compressing traffic from an active database in an active standby pair

For example, to compress replicated traffic from active database dsn1 and leave the replicated traffic from standby database dsn2 uncompressed, the CREATE ACTIVE STANDBY PAIR statement looks like:

CREATE ACTIVE STANDBY PAIR dsn1 ON "host1", dsn2 ON "host2"
SUBSCRIBER dsn3 ON "host3"
STORE dsn1 ON "host1" COMPRESS TRAFFIC ON;

Example 4-29 Compressing traffic from both active and standby databases

To compress the replicated traffic from the dsn1 and dsn2 databases, use:

CREATE ACTIVE STANDBY PAIR dsn1 ON "host1", dsn2 ON "host2"
SUBSCRIBER dsn3 ON "host3"
STORE dsn1 ON "host1" COMPRESS TRAFFIC ON
STORE dsn2 ON "host2" COMPRESS TRAFFIC ON;

Example 4-30 Compressing traffic from one database in a classic replication scheme

To compress replicated traffic from database dsn1 and leave the replicated traffic from dsn2 uncompressed, the CREATE REPLICATION statement looks like:

CREATE REPLICATION repscheme
ELEMENT d1 DATASTORE
MASTER dsn1 ON host1
SUBSCRIBER dsn2 ON host2
ELEMENT d2 DATASTORE
MASTER dsn2 ON host2
SUBSCRIBER dsn1 ON host1
STORE dsn1 ON host1 COMPRESS TRAFFIC ON;

Example 4-31 Compressing traffic between both databases in a classic replication scheme

To compress the replicated traffic between both the dsn1 and dsn2 databases, use:

CREATE REPLICATION scheme
ELEMENT d1 DATASTORE
MASTER dsn1 ON host1
SUBSCRIBER dsn2 ON host2
ELEMENT d2 DATASTORE
MASTER dsn2 ON host2
SUBSCRIBER dsn1 ON host1
STORE dsn1 ON host1 COMPRESS TRAFFIC ON
STORE dsn2 ON host2 COMPRESS TRAFFIC ON;

Port assignments

The PORT parameter for the STORE attribute of the CREATE ACTIVE STANDBY PAIR and CREATE REPLICATION statements set the port number used by a database to listen for updates from another database.

- In an active standby pair, the standby database listens for updates from the active database. Read-only subscribers listen for updates from the standby database.

- In a classic replication scheme, the subscribers listen for updates from the master database. Setting the PORT attribute for one classic replication scheme sets it for all classic replication schemes.

Static port assignments are recommended. If no PORT attribute is specified, the TimesTen daemon dynamically selects the port. When ports are assigned dynamically for the replication agents, then the ports of the TimesTen daemons have to match as well.

Note:
You must assign static ports if you want to do online upgrades.

When statically assigning ports, it is important to specify the full host name, DSN and port in the STORE attribute.

Example 4-32 Assigning static ports for an active standby pair

CREATE ACTIVE STANDBY PAIR dsn1 ON "host1", dsn2 ON "host2"
SUBSCRIBER dsn3 ON "host3"
STORE dsn1 ON "host1" PORT 16080
STORE dsn2 ON "host2" PORT 16083
STORE dsn3 ON "host3" PORT 16084;

Example 4-33 Assigning static ports for a classic replication scheme

CREATE REPLICATION repscheme
ELEMENT el1 TABLE ttuser.tab
MASTER dsn1 ON host1
SUBSCRIBER dsn2 ON host2
ELEMENT el2 TABLE ttuser.tab
MASTER dsn2 ON host2
SUBSCRIBER dsn1 ON host1
STORE dsn1 ON host1 PORT 16080
STORE dsn2 ON host2 PORT 16083;

Setting wait timeout for response from remote replication agents

The TIMEOUT store attribute sets the maximum number of seconds that the replication agent waits for a response from any remote replication agents.

We recommend that the default timeout (120 seconds) is used if you have any large transactions. The replication agent scales the timeout based on the size of the transaction in order to accommodate any large transactions that could potentially cause a delayed response from the remote replication agent. Automatic scaling by the replication agent is disabled if the user sets the TIMEOUT to less than or equal to 60 seconds.

Note:
If you experience repeated timeouts and the error log shows that multiple transmitter and receiver threads restart, then the transaction may be larger than can be scaled by the replication agent with the current timeout value. Continue to increase the timeout value until replication can progress for the transaction.

The following example creates an active standby pair whose master databases are rep1 and rep2. There is one subscriber, rep3. The type of replication is RETURN RECEIPT. The statement also sets PORT and TIMEOUT attributes for the master databases. The TIMEOUT attribute is set to 80 seconds for both the active and standby masters.

CREATE ACTIVE STANDBY PAIR rep1, rep2 RETURN RECEIPT
SUBSCRIBER rep3
STORE rep1 PORT 21000 TIMEOUT 80
STORE rep2 PORT 22000 TIMEOUT 80;

Setting the transaction log failure threshold

You can establish a threshold value that, when exceeded, sets an unavailable database to the failed state before the available transaction log space is exhausted, as follows:

- In an active standby pair, if the transaction log threshold is exceeded, sets an unavailable standby database or a read-only subscriber to the failed state before the available transaction log space is exhausted. Set the transaction log threshold by specifying the STORE clause with a FAILTHRESHOLD value in the CREATE ACTIVE STANDBY PAIR or ALTER ACTIVE STANDBY PAIR statements.
If an active database sets the standby or read-only subscriber database to the failed state, it drops all of the data for the failed database from its transaction log and transmits a message to the failed database. If the active replication agent can communicate with the replication agent of the failed database, then the message is transmitted immediately. Otherwise, the message is transmitted when the connection is reestablished.

- In a classic replication scheme, if the transaction log threshold is exceeded, sets an unavailable subscriber to the failed state before the available transaction log space is exhausted. Set the transaction log threshold by specifying the STORE clause with a FAILTHRESHOLD value in the CREATE REPLICATION or ALTER REPLICATION statements. For an example, see Example 9-5.
If a master database sets the subscriber database to the failed state, it drops all of the data for the failed subscriber from its transaction log and transmits a message to the failed subscriber database. If the master replication agent can communicate with the subscriber replication agent, then the message is transmitted immediately. Otherwise, the message is transmitted when the connection is reestablished.

However, after receiving the message from the master, if the subscriber is configured for bidirectional replication or to propagate updates to other subscribers, it does not transmit any further updates, because its replication state has been compromised.

The default threshold value is 0, which means "no limit." See "Setting connection attributes for logging" for details about transaction log failure threshold values.

Any application that connects to the failed database receives a tt_ErrReplicationInvalid (8025) warning indicating that the database has been marked failed by a replication peer. Once the database has been informed of its failed status, its state on the active or master database is changed from failed to stop.

Note:
For more information about database states, see Table 11-1, "Database states" .

An application can use the ODBC SQLGetInfo function to check if the database the application is connected to has been set to the failed state, as described in "Subscriber failures".

Suspending or resuming classic replication in response to conflicts

With classic replication, you can specify the number of replication conflicts per second at the table level at which conflict reporting is suspended and the number of conflicts per second at which conflict reporting resumes with the CONFLICT REPORTING SUSPEND and CONFLICT REPORTING RESUME attributes. For a full description, see Chapter 13, "Resolving Replication Conflicts".

Configuring the network

The following sections describe some of the issues to consider when replicating TimesTen data over a network.

- Network bandwidth requirements

- Replication in a WAN environment

- Configuring network interfaces with the ROUTE clause

- Configuring network interfaces when not using the ROUTE clause

- Identifying the local host of a replicated database

Network bandwidth requirements

The network bandwidth required for TimesTen replication depends on the bulk and frequency of the data being replicated. This discussion explores the types of transactions that characterize the high and low ends of the data range and the network bandwidth required to replicate the data between TimesTen databases.

Table 4-1 provides guidelines for calculating the size of replicated records.

Table 4-1 Replicated record sizes

Record Type

Size

Begin transaction

48 bytes

Update

116 bytes

+ 18 bytes per column updated

+ size of old column values

+ size of new column values

+ size of the primary key or unique key

Delete

104 bytes

+ size of the primary key or unique key

Insert

104 bytes

+ size of the primary key or unique key

+ size of inserted row

Transactions are sent between replicated databases in batches. A batch is created whenever there is no more data in the transaction log buffer in the master database, or when the current batch is roughly 256 KB. See "Copying updates between databases" for more information.

Replication in a WAN environment

TimesTen replication uses the TCP/IP protocol, which is not optimized for a WAN environment. You can improve replication performance over a WAN by installing a third-party "TCP stack" product. If replacing the TCP stack is not a feasible solution, you can reduce the amount of network traffic that the TCP/IP protocol has to deal with by setting the COMPRESS TRAFFIC attribute in the CREATE ACTIVE STANDBY PAIR or CREATE REPLICATION statement. See "Compressing replicated traffic" for details.

See installation information for either the AIX or Linux platforms in "AIX prerequisites" or "Linux prerequisites" in the Oracle TimesTen In-Memory Database Installation Guide for information about changing TCP/IP kernel parameters for better performance.

Configuring network interfaces with the ROUTE clause

In a replication scheme, you need to identify the name of the host on which your database resides. The operating system translates this host name to one or more IP addresses.

When specifying the host for a database in a replication element, you should always use the name returned by the hostname command, as replication uses the same host name to verify that the current host is involved in the replication scheme. Replication schemes may not be created that do not include the current host.

While you must specify the host name returned by the operating system's hostname command when you specify the database name, you can configure replication to send or receive traffic over a different interface (other than the default) using the ROUTE clause.

If a host contains multiple network interfaces (with different IP addresses), you should specify which interfaces are to be used by replication using the ROUTE clause, unless you want replication to use the default interface. You must specify a priority for each interface. Replication tries to first connect using the address with the highest priority, and if a connection cannot be established, it tries the remaining addresses in order of priority until a connection is established. If a connection to a host fails while using one IP address, replication attempts to re-connect (or fall back) to another IP address, if more than one address has been specified in the ROUTE clause.

The syntax of the ROUTE clause is:

ROUTE MASTER FullDatabaseName SUBSCRIBER FullDatabaseName
{{MASTERIP MasterHost | SUBSCRIBERIP SubscriberHost}
PRIORITY Priority} [...]

Note:
Addresses for the ROUTE clause may be specified as either host names or IP addresses. However, if your host has more than one IP address configured for a given host name, you should only configure the ROUTE clause using the IP addresses, in order to ensure that replication uses only the IP addresses that you intend.

- When using the ROUTE clause in an active standby pair, each master database is a subscriber of the other master database and each read-only subscriber is a subscriber of both master databases. This means that the CREATE ACTIVE STANDBY PAIR statement should include ROUTE clauses in multiples of two to specify a route in both directions.

- When using the ROUTE clause in a classic replication scheme that defines dual masters, each master database is a subscriber of the other master database. This means that the CREATE REPLICATION statement should include ROUTE clauses in multiples of two to specify a route in both directions.

Example 4-34 Configuring multiple network interfaces for an active standby pair

If host1 host is configured with a second interface accessible by the host1fast host name, and host2 is configured with a second interface at IP address 192.168.1.100, you may specify that the secondary interfaces are used with the replication scheme.

CREATE ACTIVE STANDBY PAIR dns1, dsn2
ROUTE MASTER dsn1 ON "host1" SUBSCRIBER dsn2 ON "host2"
MASTERIP "host1fast" PRIORITY 1
SUBSCRIBERIP "192.168.1.100" PRIORITY 1
ROUTE MASTER dsn2 ON "host2" SUBSCRIBER dsn1 ON "host1"
MASTERIP "192.168.1.100" PRIORITY 1
SUBSCRIBERIP "host1fast" PRIORITY 1;

Example 4-35 Configuring multiple network interfaces for a classic replication scheme

If host1 host is configured with a second interface accessible by the host1fast host name, and host2 is configured with a second interface at IP address 192.168.1.100, you may specify that the secondary interfaces are used with the replication scheme.

CREATE REPLICATION repscheme
ELEMENT e1 TABLE ttuser.tab
MASTER dsn1 ON host1
SUBSCRIBER dsn2 ON host2
ELEMENT e2 TABLE ttuser.tab
MASTER dsn2 ON host2
SUBSCRIBER dsn1 ON host1
ROUTE MASTER dsn1 ON host1 SUBSCRIBER dsn2 ON host2
MASTERIP host1fast PRIORITY 1
SUBSCRIBERIP "192.168.1.100" PRIORITY 1
ROUTE MASTER dsn2 ON host2 SUBSCRIBER dsn1 ON host1
MASTERIP "192.168.1.100" PRIORITY 1
SUBSCRIBERIP host1fast PRIORITY 1;

Alternately, on a replication host with more than one interface, you may want to configure replication to use one or more interfaces as backups, in case the primary interface fails or the connection from it to the receiving host is broken. You can use the ROUTE clause to specify two or more interfaces for each master or subscriber that are used by replication in order of priority.

If replication on the master host is unable to bind to the MASTERIP with the highest priority, it tries to connect using subsequent MASTERIP addresses in order of priority immediately. However, if the connection to the subscriber fails for any other reason, replication tries to connect using each of the SUBSCRIBERIP addresses in order of priority before it tries the MASTERIP address with the next highest priority.

Example 4-36 Configuring network priority on an active standby pair

If the host1 host is configured with two network interfaces at IP addresses 192.168.1.100 and 192.168.1.101, and the host2 host is configured with two interfaces at IP addresses 192.168.1.200 and 192.168.1.201, you may specify that replication use IP addresses 192.168.1.100 and 192.168.200 to transmit and receive traffic first, and to try IP addresses 192.168.1.101 or 192.168.1.201 if the first connection fails.

CREATE ACTIVE STANDBY PAIR dns1, dns2
ROUTE MASTER dsn1 ON "host1" SUBSCRIBER dsn2 ON "host2"
MASTERIP "192.168.1.100" PRIORITY 1
MASTERIP "192.168.1.101" PRIORITY 2
SUBSCRIBERIP "192.168.1.200" PRIORITY 1
SUBSCRIBERIP "192.168.1.201" PRIORITY 2;

Example 4-37 Configuring network priority for a classic replication scheme

If the host1 host is configured with two network interfaces at IP addresses 192.168.1.100 and 192.168.1.101, and the host2 host is configured with two interfaces at IP addresses 192.168.1.200 and 192.168.1.201, you may specify that replication use IP addresses 192.168.1.100 and 192.168.200 to transmit and receive traffic first, and to try IP addresses 192.168.1.101 or 192.168.1.201 if the first connection fails.

CREATE REPLICATION repscheme
ELEMENT e TABLE ttuser.tab
MASTER dsn1 ON host1
SUBSCRIBER dsn2 ON host2
ROUTE MASTER dsn1 ON host1 SUBSCRIBER dsn2 ON host2
MASTERIP "192.168.1.100" PRIORITY 1
MASTERIP "192.168.1.101" PRIORITY 2
SUBSCRIBERIP "192.168.1.200" PRIORITY 1
SUBSCRIBERIP "192.168.1.201" PRIORITY 2;

Configuring network interfaces when not using the ROUTE clause

The following sections describe how to configure replication so that it uses the correct host names and IP addresses for each host when not using the ROUTE clause.

- Identifying database hosts on UNIX without using the ROUTE clause

- Host name resolution on Windows

- User-specified addresses for TimesTen daemons and subdaemons

Identifying database hosts on UNIX without using the ROUTE clause

When possible, you should use the ROUTE clause of a replication scheme to identify database hosts and the network interfaces to use for replication. However, if you have a replication scheme configuration that does not use the ROUTE clause, this section explains how to configure operating system and DNS files for a replication host with multiple network interfaces.

If a host contains multiple network interfaces (with different IP addresses) and replication is not configured with a ROUTE clause, TimesTen replication tries to connect to the IP addresses in the same order as returned by the gethostbyname call. It tries to connect using the first address; if a connection cannot be established, it tries the remaining addresses in order until a connection is established. TimesTen replication uses this same sequence each time it establishes a new connection to a host. If a connection to a host fails on one IP address, TimesTen replication attempts to re-connect (or fall back) to another IP address for the host in the same manner described above.

There are two basic ways you can configure a host to use multiple IP addresses on UNIX platforms: DNS or the /etc/hosts file.

Note:
If you have multiple network interface cards (NICs), be sure that "multi on" is specified in the /etc/host.conf file. Otherwise, gethostbyname cannot return multiple addresses.

For example, if your machine has two NICs, use the following syntax for your /etc/hosts file:

127.0.0.1  localhost
IP_address_for_NIC_1  official_hostname optional_alias
IP_address_for_NIC_2  official_hostname optional_alias

The host name official_hostname is the name returned by the hostname command.

When editing the /etc/hosts file, keep in mind that:

- You must log in as root to change the /etc/hosts file.

- There should only be one line per IP address.

- There can be multiple alias names on each line.

- When there are multiple IP addresses for the same host name, they must be on consecutive lines.

- The host name can be up to 30 characters long.

For example, the following entry in the /etc/hosts file on a UNIX platform describes a server named Host1 with two IP addresses:

127.0.0.1        localhost
10.10.98.102     Host1
192.168.1.102    Host1

To specify the same configuration for DNS, your entry in the domain zone file would look like:

Host1     IN     A     10.10.98.102
IN     A     192.168.1.102

In either case, you only need to specify Host1 as the host name in your replication scheme and replication uses the first available IP address when establishing a connection.

In an environment in which multiple IP addresses are used, you can also assign multiple host names to a single IP address in order to restrict a replication connection to a specific IP address. For example, you might have an entry in your /etc/hosts file that looks like:

127.0.0.1        localhost
10.10.98.102     Host1
192.168.1.102    Host1 RepHost1

or a DNS zone file that looks like:

Host1     IN     A     10.10.98.102
IN     A     192.168.1.102
RepHost1  IN     A     192.168.1.102

If you want to restrict replication connections to IP address 192.168.1.102 for this host, you can specify RepHost1 as the host name in your replication scheme. Another option is to simply specify the IP address as the host name in either the CREATE ACTIVE STANDBY PAIR or CREATE REPLICATION statements used to configure your replication scheme.

Host name resolution on Windows

If a replication configuration is specified using host names rather than IP addresses, replication must be able to translate host names of peers into IP addresses. For this to happen efficiently on Windows, make sure each Windows machine is set up to query either a valid WINS server or a valid DNS server that has correct information about the hosts on the network. In the absence of such servers, static host-to-IP entries can be entered in either:

%windir%\system32\drivers\etc\hosts

or

%windir%\system32\drivers\etc\lmhosts

Without any of these options, a Windows machine resorts to broadcasting to detect peer nodes, which is extremely slow.

You may also encounter extremely slow host name resolution if the Windows machine cannot communicate with the defined WINS servers or DNS servers, or if the host name resolution set up is incorrect on those servers. Use the ping command to test whether a host can be efficiently located. The ping command responds immediately if host name resolution is set up properly.

Note:
You must be consistent in identifying a database host in a replication scheme. Do not identify a host using its IP address for one database and then use its host name for the same or another database.

User-specified addresses for TimesTen daemons and subdaemons

By default, the TimesTen main daemon, all subdaemons, and all agents use any available address to listen on a socket for requests. You can modify the ttendaemon.options file to specify an address for communication among the agents and daemons by including a -listenaddr option. See "Managing TimesTen daemon options" in Oracle TimesTen In-Memory Database Operations Guide for details.

Suppose that your machine has two NICs whose addresses are 10.10.10.100 and 10.10.11.200. The loopback address is 127.0.0.1. Then keep in mind the following as it applies to the replication agent:

- If you do not set the -listenaddr option in the ttendaemon.options file, then any process can talk to the daemons and agents.

- If you set -listenaddr to 10.10.10.100, then any process on the local host or the 10.10.10 net can talk to daemons and agents on 10.10.10.100. No processes on the 10.10.11 net can talk to the daemons and agents on 10.10.10.100.

- If you set -listenaddr to 127.0.0.1, then only processes on the local host can talk to the daemons and agents. No processes on other hosts can talk the daemons and agents.

Identifying the local host of a replicated database

Ordinarily, TimesTen replication is able to identify the hosts involved in a replication configuration using normal operating system host name resolution methods. However, in some rare instances, if the host has an unusual host name configuration, TimesTen is unable to determine that the local host matches the host name as specified in the replication scheme. When this occurs, you receive error 8191, "This store is not involved in a replication scheme," when attempting to start replication using ttRepStart or ttAdmin -repStart. The ttHostNameSet built-in procedure may be used in this instance to explicitly indicate to TimesTen that the current database is in fact the database specified in the replication scheme. See "ttHostNameSet" in Oracle TimesTen In-Memory Database Reference for more information.

5 Administering an Active Standby Pair without Cache Groups

This chapter describes how to administer an active standby pair that does not replicate cache groups. For information about administering active standby pairs that replicate cache groups, see Chapter 6, "Administering an Active Standby Pair with Cache Groups".

For information about managing failover and recovery automatically, see Chapter 8, "Using Oracle Clusterware to Manage Active Standby Pairs".

This chapter includes the following topics:

- Setting up an active standby pair with no cache groups

- Recovering from a failure of the active database

- Recovering from a failure of the standby database

- Recovering after a dual failure of both active and standby databases

- Recovering from the failure of a subscriber database

- Reversing the roles of the active and standby databases

- Detection of dual active databases

Setting up an active standby pair with no cache groups

To set up an active standby pair, complete the tasks in this section. See "Configuring an active standby pair with one subscriber" for an example.

Note:
If you intend to replicate read-only cache groups or asynchronous writethrough (AWT) cache groups, see Chapter 6, "Administering an Active Standby Pair with Cache Groups".

Before you create a database, see the information in these sections:

- "Configuring the network"

- "Connection attributes for replicated databases"

- "Managing the transaction log on a replicated database"

1. Create a database. See "Managing TimesTen Databases" in Oracle TimesTen In-Memory Database Operations Guide.

2. Create the replication scheme using the CREATE ACTIVE STANDBY PAIR statement. See Chapter 3, "Defining an Active Standby Pair Replication Scheme".

3. Call ttRepStateSet('ACTIVE') on the active database.

4. Start the replication agent. See "Starting and stopping the replication agents".

5. Create a user on the active database and grant the ADMIN privilege to the user.

6. Duplicate the active database to the standby database.

7. Start the replication agent on the standby database. See "Starting and stopping the replication agents".

8. Wait for the standby database to enter the STANDBY state. Use the ttRepStateGet built-in procedure to check the state of the standby database.

9. Duplicate all of the subscribers from the standby database. See "Duplicating a master database to a subscriber".

10. Set up the replication agent policy and start the replication agent on each of the subscriber databases. See "Starting and stopping the replication agents".

Recovering from a failure of the active database

This section includes the following topics:

- Recovering when the standby database is ready

- Failing back to the original nodes

Recovering when the standby database is ready

This section describes how to recover the active database when the standby database is available and synchronized with the active database. It includes the following topics:

- When replication is return receipt or asynchronous

- When replication is return twosafe

When replication is return receipt or asynchronous

Complete the following tasks:

1. Stop the replication agent on the failed database if it has not already been stopped.

2. On the standby database, call ttRepStateSet('ACTIVE'). This changes the role of the database from STANDBY to ACTIVE.

3. On the new active database, call ttRepStateSave('FAILED', 'failed_database','host_name'), where failed_database is the former active database that failed. This step is necessary for the new active database to replicate directly to the subscriber databases. During normal operation, only the standby database replicates to the subscribers.

4. Destroy the failed database.

5. Duplicate the new active database to the new standby database.

6. Set up the replication agent policy and start the replication agent on the new standby database. See "Starting and stopping the replication agents".

The standby database contacts the active database. The active database stops sending updates to the subscribers. When the standby database is fully synchronized with the active database, then the standby database enters the STANDBY state and starts sending updates to the subscribers.

Note:
You can verify that the standby database has entered the STANDBY state by using the ttRepStateGet built-in procedure.

When replication is return twosafe

Complete the following tasks:

1. On the standby database, call ttRepStateSet('ACTIVE'). This changes the role of the database from STANDBY to ACTIVE.

2. On the new active database, call ttRepStateSave('FAILED', 'failed_database','host_name'), where failed_database is the former active database that failed. This step is necessary for the new active database to replicate directly to the subscriber databases. During normal operation, only the standby database replicates to the subscribers.

3. Connect to the failed database. This triggers recovery from the local transaction logs. If database recovery fails, you must continue from Step 5 of the procedure for recovering when replication is return receipt or asynchronous. See "When replication is return receipt or asynchronous".

4. Verify that the replication agent for the failed database has restarted. If it has not restarted, then start the replication agent. See "Starting and stopping the replication agents".

When the active database determines that it is fully synchronized with the standby database, then the standby database enters the STANDBY state and starts sending updates to the subscribers.

Note:
You can verify that the standby database has entered the STANDBY state by using the ttRepStateSet built-in procedure.

Failing back to the original nodes

After a successful failover, you may want to fail back so that the active database and the standby database are on their original nodes. See "Reversing the roles of the active and standby databases" for instructions.

Recovering from a failure of the standby database

To recover from a failure of the standby database, complete the following tasks:

1. Detect the standby database failure.

2. If return twosafe service is enabled, the failure of the standby database may prevent a transaction in progress from being committed on the active database, resulting in error 8170, "Receipt or commit acknowledgement not returned in the specified timeout interval". If so, then call the ttRepSyncSet built-in procedure with a localAction parameter of 2 (COMMIT) and commit the transaction again. For example:

Command> call ttRepSyncSet( null, null, 2);
Command> commit;

3. Call ttRepStateSave('FAILED','standby_database','host_name') on the active database. Afterwards, as long as the standby database is unavailable, updates to the active database are replicated directly to the subscriber databases. Subscriber databases may also be duplicated directly from the active.

4. If the replication agent for the standby database has automatically restarted, stop the replication agent. See "Starting and stopping the replication agents".

5. Recover the standby database in one of the following ways:

- Connect to the standby database. This triggers recovery from the local transaction logs.

- Duplicate the standby database from the active database.

The amount of time that the standby database has been down and the amount of transaction logs that need to be applied from the active database determine the method of recovery that you should use.

6. Set up the replication agent policy and start the replication agent on the new standby database. See "Starting and stopping the replication agents".

The standby database enters the STANDBY state and starts sending updates to the subscribers after the active database determines that the two master databases have been synchronized and stops sending updates to the subscribers.

Note:
You can verify that the standby database has entered the STANDBY state by using the ttRepStateGet built-in procedure.

Recovering after a dual failure of both active and standby databases

Consider the following scenarios:

- The standby database fails. Then, the active database fails before the standby comes back up or before the standby has been synchronized with the active database.

- The active database fails. The standby database becomes ACTIVE, and the rest of the recovery process begins. (See "Recovering from a failure of the active database".) The new active database fails before the new standby database is fully synchronized with it.

In both scenarios, the subscribers may have had more changes applied than the standby database.

When the active database fails and the standby database has not applied all of the changes that were last sent from the active database, there are two choices for recovery:

- Recover the active database from the local transaction logs.

- Recover the standby database from the local transaction logs.

The choice depends on which database is available and which is more up to date.

Recover the active database

1. Connect to the failed active database. This triggers recovery from the local transaction logs.

2. Verify that the replication agent for the failed active database has restarted. If it has not restarted, then start the replication agent. See "Starting and stopping the replication agents".

3. Call ttRepStateSet('ACTIVE') on the newly recovered database.

4. Continue with Step 6 in "Setting up an active standby pair with no cache groups".

Recover the standby database

1. Connect to the failed standby database. This triggers recovery from the local transaction logs.

2. If the replication agent for the standby database has automatically restarted, you must stop the replication agent. See "Starting and stopping the replication agents".

3. Drop the replication configuration using the DROP ACTIVE STANDBY PAIR statement.

4. Re-create the replication configuration using the CREATE ACTIVE STANDBY PAIR statement.

5. Call ttRepStateSet('ACTIVE') on the master database, giving it the ACTIVE role.

6. Set up the replication agent policy and start the replication agent on the new standby database. See "Starting and stopping the replication agents".

7. Continue from Step 6 in "Setting up an active standby pair with no cache groups".

Recovering from the failure of a subscriber database

If a subscriber database fails, then you can recover it by one of the following methods:

- Connect to the failed subscriber. This triggers recovery from the local transaction logs. Start the replication agent and let the subscriber catch up.

- Duplicate the subscriber from the standby database.

If the standby database is down or in recovery, then duplicate the subscriber from the active database.

After the subscriber database has been recovered, then set up the replication agent policy and start the replication agent. See "Starting and stopping the replication agents".

Reversing the roles of the active and standby databases

To change the role of the active database to standby and vice versa:

1. Pause any applications that are generating updates on the current active database.

2. Call ttRepSubscriberWait on the active database, with the DSN and host of the current standby database as input parameters. It must return success (<00>). This ensures that all updates have been transmitted to the current standby database.

3. Stop the replication agent on the current active database. See "Starting and stopping the replication agents".

4. Call ttRepDeactivate on the current active database. This puts the database in the IDLE state.

5. Call ttRepStateSet('ACTIVE') on the current standby database. This database now acts as the active database in the active standby pair.

6. Set up the replication agent policy and start the replication agent on the old active database.

7. Use the ttRepStateGet built-in procedure to determine when the database's state has changed from IDLE to STANDBY. The database now acts as the standby database in the active standby pair.

8. Resume any applications that were paused in Step 1.

Detection of dual active databases

Ordinarily, the designation of the active and standby databases in an active standby pair is explicitly controlled by the user. However, in some circumstances the user may not have the ability to modify both the active and standby databases when changing the role of the standby database to active.

For example, if network communication to the site of an active database is interrupted, the user may need the standby database at a different site to take over the role of the active, but cannot stop replication on the current active or change its role manually. Changing the standby database to active without first stopping replication on the active leads to a situation where both masters are in the ACTIVE state and accepting transactions. In such a scenario, TimesTen can automatically negotiate the active/standby role of the master databases when network communication between the databases is restored.

If, during the initial handshake between the databases, TimesTen determines that the master databases in an active standby pair replication scheme are both in the ACTIVE state, TimesTen performs the following operations automatically:

- The database which was set to the ACTIVE state most recently is left in the ACTIVE state and may continue to be connected to and updated by applications.

- The database which was set to the ACTIVE state least recently is invalidated. All applications are disconnected.

- When the invalidated database comes back up, TimesTen determines whether any transactions have occurred on the database that have not yet been replicated to the other master database. If such transactions have occurred, they are now trapped, and the database is left in the IDLE state. The database needs to be duplicated from the active in order to become a standby. If there are no trapped transactions, the database is safe to use as a standby database and is automatically set to the STANDBY state.

6 Administering an Active Standby Pair with Cache Groups

You can replicate tables within either a read-only cache group or an asynchronous writethrough (AWT) cache group as long as they are configured within an active standby pair.

Note:
For information about managing failover and recovery automatically, see Chapter 8, "Using Oracle Clusterware to Manage Active Standby Pairs".

The following sections describe how to administer an active standby pair that replicates cache groups:

- Active standby pairs with cache groups

- Setting up an active standby pair with a read-only cache group

- Setting up an active standby pair with an AWT cache group

- Changing user names or passwords used by replication

- Recovering from a failure of the active database

- Recovering from a failure of the standby database

- Recovering after a dual failure of both active and standby databases

- Recovering from the failure of a subscriber database

- Reversing the roles of the active and standby databases

- Detecting dual active databases

- Using a disaster recovery subscriber in an active standby pair

Active standby pairs with cache groups

An active standby pair that replicates a read-only cache group or an asynchronous writethrough (AWT) cache group can change the role of the cache group automatically as part of failover and recovery. This helps ensure high availability of cache instances with minimal data loss. See "Replicating an AWT cache group" and "Replicating a read-only cache group".

Note:
TimesTen does not support replication of a user managed cache group or a synchronous writethrough (SWT) cache group in an active standby pair.

You can also create a special disaster recovery read-only subscriber when you set up active standby replication of an AWT cache group. This special subscriber, located at a remote disaster recovery site, can propagate updates to a second Oracle database, also located at the disaster recovery site. See "Using a disaster recovery subscriber in an active standby pair".

Setting up an active standby pair with a read-only cache group

This section describes how to set up an active standby pair that replicates cache tables in a read-only cache group. The active standby pair used as an example in this section is not a cache grid member.

Before you create a database, see the information in these sections:

- "Configuring the network"

- "Connection attributes for replicated databases"

- "Managing the transaction log on a replicated database"

To set up an active standby pair that replicates a local read-only cache group, complete the following tasks:

1. Create a cache administration user in the Oracle database. See "Create users in the Oracle database" in Oracle TimesTen Application-Tier Database Cache User's Guide.

2. Create a database. See "Create a DSN for the TimesTen database" in Oracle TimesTen Application-Tier Database Cache User's Guide.

3. Set the cache administration user ID and password by calling the ttCacheUidPwdSet built-in procedure. See "Set the cache administration user name and password in the TimesTen database" in Oracle TimesTen Application-Tier Database Cache User's Guide. For example:

Command> call ttCacheUidPwdSet('orauser','orapwd');

4. Start the cache agent on the database. Use the ttCacheStart built-in procedure or the ttAdmin -cachestart utility.

Command> call ttCacheStart;

5. Use the CREATE CACHE GROUP statement to create the read-only cache group. For example:

Command> CREATE READONLY CACHE GROUP readcache
> AUTOREFRESH INTERVAL 5 SECONDS
> FROM oratt.readtab
> (keyval NUMBER NOT NULL PRIMARY KEY, str VARCHAR2(32));

6. Ensure that the autorefresh state is set to PAUSED. The autorefresh state is PAUSED by default after cache group creation. You can verify the autorefresh state by executing the ttIsql cachegroups command:

Command> cachegroups;

7. Create the replication scheme using the CREATE ACTIVE STANDBY PAIR statement.
For example, suppose master1 and master2 are defined as the master databases. sub1 and sub2 are defined as the subscriber databases. The databases reside on node1, node2, node3, and node4. The return service is RETURN RECEIPT. The replication scheme can be specified as follows:

Command> CREATE ACTIVE STANDBY PAIR master1 ON "node1", master2 ON "node2"
> RETURN RECEIPT
> SUBSCRIBER sub1 ON "node3", sub2 ON "node4"
> STORE master1 ON "node1" PORT 21000 TIMEOUT 30
> STORE master2 ON "node2" PORT 20000 TIMEOUT 30;

8. Set the replication state to ACTIVE by calling the ttRepStateSet built-in procedure on the active database (master1). For example:

Command> call ttRepStateSet('ACTIVE');

9. Set up the replication agent policy for master1 and start the replication agent. See "Starting and stopping the replication agents".

10. Load the cache group by using the LOAD CACHE GROUP statement. This starts the autorefresh process. For example:

Command> LOAD CACHE GROUP readcache COMMIT EVERY 256 ROWS;

11. As the instance administrator, duplicate the active database (master1) to the standby database (master2). Use the ttRepAdmin -duplicate utility with the -keepCG option to preserve the cache group. Alternatively, you can use the ttRepDuplicateEx C function to duplicate the database. See "Duplicating a database". ttRepAdmin prompts for the values of -uid, -pwd, -cacheuid and -cachepwd.

ttRepAdmin -duplicate -from master1 -host node1 -keepCG
-connStr "DSN=master2;UID=;PWD="

12. Set up the replication agent policy on master2 and start the replication agent. See "Starting and stopping the replication agents".

13. The standby database enters the STANDBY state automatically. Wait for master2 to enter the STANDBY state. Call the ttRepStateGet built-in procedure to check the state of master2. For example:

Command> call ttRepStateGet;

14. Start the cache agent for master2 using the ttCacheStart built-in procedure or the ttAdmin -cacheStart utility. For example:

Command> call ttCacheStart;

15. As the instance administrator, duplicate the subscribers (sub1 and sub2) from the standby database (master2). Use the -noKeepCG command line option with ttRepAdmin -duplicate to convert the cache tables to normal TimesTen tables on the subscribers. ttRepAdmin prompts for the values of -uid and -pwd. See "Duplicating a database". For example:

ttRepAdmin -duplicate -from master2 -host node2 -nokeepCG
-connStr "DSN=sub1;UID=;PWD="

16. Set up the replication agent policy on the subscribers and start the replication agent on each of the subscriber databases. See "Starting and stopping the replication agents".

Setting up an active standby pair with an AWT cache group

For detailed instructions for setting up an active standby pair with a global AWT cache group, see "Replicating cache tables" in Oracle TimesTen Application-Tier Database Cache User's Guide. The active standby pair in that section is a cache grid member.

Changing user names or passwords used by replication

In the active standby pair, you can modify either the TimesTen user name or password or (if there are cache groups in the active standby pair) the user names and passwords for the TimesTen cache manager user, its companion Oracle user, or the cache administration user.

When the DDLReplicationLevel connection attribute is 2 or larger, changes to the user names or passwords executed on the active master are automatically replicated to the standby master and any subscribers. When the DDLReplicationLevel connection attribute is 1, changes to the user names or passwords executed on the active master are not automatically replicated to the standby master and any subscribers. In this case, you must manually execute each SQL statement on the active master, standby master, and any subscribers.

Note:
For more information on what DDL statements are automatically replicated for the different values of the DDLReplicationLevel connection attribute, see "Making DDL changes in an active standby pair".

Perform the following to change any of the user names or passwords for the TimesTen user or, if there are cache groups in the active standby pair, for the TimesTen cache manager user, its companion Oracle user, or the cache administration user:

1. If you want to modify a password of a TimesTen user, use the ALTER USER statement on the active master database. If you want to change the TimesTen user name, you must first drop all objects that the TimesTen user owns before dropping the user name and creating a new user.
To modify the password of the oratt user:

Note:
See "Creating or identifying users to the database" in Oracle TimesTen In-Memory Database Operations Guide.

Command> ALTER USER oratt IDENTIFIED BY newpwd;

2. If you want to modify any of the user names or passwords used for cache operations (such as the cache administration user, the cache manager user or its companion Oracle user), perform the instructions provided in "Changing cache user names or passwords" in the Oracle TimesTen Application-Tier Database Cache User's Guide.

Recovering from a failure of the active database

If the active master has failed and the standby database did not fail or has recovered after a failure, then the following sections describe how to recover the active standby pair by making the standby master the new active master. In addition, you can then swap the active and standby masters again so that they exist on the original nodes.

- Recovering when the standby database is ready

- Failing back to the original nodes

Note:
If both the active and standby masters fail, see "Recovering after a dual failure of both active and standby databases" for instructions on how to recover.

Recovering when the standby database is ready

The first two sections describe how to recover the active database when the standby database is available and synchronized with the active database. The last section describes what to do if following the instructions from either of the first two sections fails; the standby database is available, but the data is not fully synchronized.

- When replication is return receipt or asynchronous

- When replication is return twosafe

- When there is unsynchronized data in the cache groups

When replication is return receipt or asynchronous

Complete the following tasks:

1. On the standby database, stop the replication agent if it has not already been stopped.

2. On the standby database, call ttRepStateSet('ACTIVE'). This changes the role of the database from STANDBY to ACTIVE. If you are replicating a read-only cache group, this action automatically causes the autorefresh state to change from PAUSED to ON for this database.

3. On the new active database, call ttRepStateSave('FAILED', 'failed_database','host_name'), where failed_database is the former active database that failed. This step is necessary for the new active database to replicate directly to the subscriber databases. During normal operation, only the standby database replicates to the subscribers.

4. On the new active database, start the replication agent and the cache agent.

5. Destroy the failed database (the old active) with the ttDestroy utility.

6. Duplicate the new active database to the new standby database. You can use either the ttRepAdmin -duplicate utility or the ttRepDuplicateEx C function to duplicate a database. Use the -keepCG -recoveringNode options with ttRepAdmin to recover and to preserve the cache group after the active master failure. See "Duplicating a database".

7. Set up the replication agent policy on the new standby database and start the replication agent. See "Starting and stopping the replication agents".

8. Start the cache agent on the new standby database.

Note:
If any of these steps failed, follow the directions in "When there is unsynchronized data in the cache groups".

The standby database contacts the active database. The active database stops sending updates to the subscribers. When the standby database is fully synchronized with the active database, then the standby database enters the STANDBY state and starts sending updates to the subscribers.The new standby database takes over processing of the cache group automatically when it enters the STANDBY state. If you are replicating an AWT cache group, the new standby database takes over processing of the cache group automatically when it enters the STANDBY state.

Note:
You can verify that the standby database has entered the STANDBY state by using the ttRepStateGet built-in procedure.

When replication is return twosafe

Complete the following tasks:

1. Stop the replication agent on the standby database if it has not already been stopped.

2. On the standby database, call ttRepStateSet('ACTIVE'). This changes the role of the database from STANDBY to ACTIVE. If you are replicating a read-only cache group, this action automatically causes the autorefresh state to change from PAUSED to ON for this database.

3. On the new active database, call ttRepStateSave('FAILED', 'failed_database','host_name'), where failed_database is the former active database that failed. This step is necessary for the new active database to replicate directly to the subscriber databases. During normal operation, only the standby database replicates to the subscribers.

4. On the new active database, start the replication agent and the cache agent.

5. Connect to the failed database. This triggers recovery from the local transaction logs. If database recovery fails, you must continue from Step 5 of the procedure for recovering when replication is return receipt or asynchronous. See "When replication is return receipt or asynchronous". If you are replicating a read-only cache group, the autorefresh state is automatically set to PAUSED.

6. Verify that the replication agent for the failed database has restarted. If it has not restarted, then start the replication agent. See "Starting and stopping the replication agents".

7. Verify that the cache agent for the failed database has restarted. If it has not restarted, then start the cache agent.

Note:
If any of these steps failed, follow the directions in "When there is unsynchronized data in the cache groups".

When the active database determines that it is fully synchronized with the standby database, then the standby database enters the STANDBY state and starts sending updates to the subscribers. The new standby database takes over processing of the cache group automatically when it enters the STANDBY state. If you are replicating an AWT cache group, the new standby database takes over processing of the cache group automatically when it enters the STANDBY state.

Note:
You can verify that the standby database has entered the STANDBY state by using the ttRepStateSet built-in procedure.

When there is unsynchronized data in the cache groups

If the steps in either "When replication is return receipt or asynchronous" or "When replication is return twosafe" fail, then there could be unsynchronized data in the AWT cache groups that has not been propagated to the Oracle database. In addition, there could be unsynchronized data on the Oracle database that has not been uploaded to any read-only cache groups that are included in the active standby pair replication scheme.

If there is data in any AWT cache groups on the standby master that has not been propagated when the active database failed, then simply recovering the standby database as the new active database is not an option. In this case, perform the following:

1. On the standby database, stop the replication agent and drop the replication configuration using the DROP ACTIVE STANDBY PAIR statement.

2. Stop the cache agent to ensure that no more updates are applied to the AWT cache groups while performing this recovery operation and to ensure that you control when any read-only cache groups that were included in the replication scheme are refreshed.

3. For any read-only cache groups that are included in the replication scheme, set the autorefresh state to pause with the ALTER CACHE GROUP ... SET AUTOREFRESH STATE PAUSED statement.

4. On the standby database, flush any unpropagated committed inserts or updates on TimesTen cache tables for any AWT cache groups to the cached Oracle Database tables, as follows:

1. Set autocommit to off.

2. Call the ttCacheAllowFlushAwtSet built-in procedure with the parameter set to 1. This built-in procedure allows you to execute a FLUSH CACHE GROUP statement against an AWT cache group and should only be used in this recovery scenario.

Command> call ttCacheAllowFlushAwtSet(1);

3. Execute the FLUSH CACHE GROUP SQL statement against each AWT cache group to ensure that all data is propagated to the Oracle database.

Note:
Executing the FLUSH CACHE GROUP statement under these conditions on the AWT cache group only flushes the contents of the tables in the AWT cache group; that is, the data that was either inserted or updated. It does not take into account any delete operations. So, you may have rows that exist on the Oracle database that were deleted from the AWT cache group. It is up to the user to recover any delete operations.

4. Call the ttCacheAllowFlushAwtSet built-in procedure with the parameter set to 0 to disallow any future execution of the FLUSH CACHE GROUP statement on an AWT cache group.

Command> call ttCacheAllowFlushAwtSet(0);

5. Commit after calling the ttCacheAllowFlushAwtSet built-in procedure with the parameter set to 0. You can also choose to reset autocommit to on, as it only needed to be off for the ttCacheAllowFlushAwtSet built-in procedure.

5. Drop and re-create all AWT cache groups using the DROP CACHE GROUP and CREATE CACHE GROUP statements.

6. Start the replication agent and the cache agent, since the cache agent needs to be active to refresh any read-only cache groups and both must be active in order to load the AWT cache groups.

7. Refresh all read-only cache groups using the REFRESH CACHE GROUP statement to upload most current committed data from the cached Oracle database tables. Use the REFRESH CACHE GROUP ... PARALLEL n clause to concurrently load these cache groups over multiple threads.

8. Load all AWT cache groups using the LOAD CACHE GROUP statement to begin the autorefresh process. Use the LOAD CACHE GROUP ... PARALLEL n clause to concurrently load these cache groups over multiple threads.

9. Stop both the replication agent and the cache agent in preparation to re-create the active standby pair.

10. Re-create the replication configuration on the standby database using the CREATE ACTIVE STANDBY PAIR statement.

11. Set the old standby database as the new active database, destroy the failed old active database, perform a duplicate of the active to create a new standby database, and start the cache and replication agents on the standby as described in the steps listed in "When replication is return receipt or asynchronous".

Failing back to the original nodes

After a successful failover, you may want to fail back so that the active database and the standby database are on their original nodes. See "Reversing the roles of the active and standby databases" for instructions.

Recovering from a failure of the standby database

To recover from a failure of the standby database, complete the following tasks:

1. If return twosafe service is enabled, the failure of the standby database may prevent a transaction in progress from being committed on the active database, resulting in error 8170, "Receipt or commit acknowledgement not returned in the specified timeout interval". If so, then call the ttRepSyncSet built-in procedure with a localAction parameter of 2 (COMMIT) and commit the transaction again. For example:

Command> call ttRepSyncSet( null, null, 2);
Command> commit;

2. Call ttRepStateSave('FAILED','standby_database','host_name') on the active database. Then, as long as the standby database is unavailable, updates to the active database are replicated directly to the subscriber databases. Additional subscriber databases may also be duplicated directly from the active.

3. Recover the standby database in one of the following ways:

1. Connect to the standby database. This triggers recovery from the local transaction logs. If the standby database recovers, go to Step 4; otherwise, continue to Step 3b.

2. Destroy the current version of the standby database with the ttDestroy utility.

3. Duplicate a new standby database from the active database. You can use either the ttRepAdmin -duplicate utility or the ttRepDuplicateEx C function to duplicate a database. Use the -keepCG -recoveringNode options with ttRepAdmin to recover and to preserve the cache group after the standby master failure. See "Duplicating a database".

4. Set up the replication agent policy and start the replication agent on the standby database. See "Starting and stopping the replication agents".

5. Start the cache agent on the standby database.

The standby database enters the STANDBY state and starts sending updates to the subscribers after the active database determines that the two master databases have been synchronized and stops sending updates to the subscribers.

Note:
You can verify that the standby database has entered the STANDBY state by using the ttRepStateGet built-in procedure.

Recovering after a dual failure of both active and standby databases

If both the active and standby databases fail at around the same time and if you can reconnect to both of them almost immediately, then restart the replication agents (and cache agents if applicable) and continue.

1. Connect to the failed active database. This triggers recovery from the local transaction logs. If you are replicating a read-only cache group, the autorefresh state is automatically set to PAUSED.

2. Verify that the replication agent for the failed active database has restarted. If it has not restarted, then start the replication agent. See "Starting and stopping the replication agents".

3. Call ttRepStateSet('ACTIVE') on the newly recovered database. If you are replicating a read-only cache group, this action automatically causes the autorefresh state to change from PAUSED to ON for this database.

4. Verify that the cache agent for the failed database has restarted. If it has not restarted, then start the cache agent.

5. Connect to the failed standby master database. This triggers recovery from the local transaction logs. If you are replicating a read-only cache group, the autorefresh state is automatically set to PAUSED.

6. Verify that the replication agent for the failed standby database has restarted. If it has not restarted, then start the replication agent. See "Starting and stopping the replication agents".

7. Verify that the cache agent for the failed standby database has restarted. If it has not restarted, then start the cache agent.

Alternatively, consider the following scenarios where both the active and standby master databases fail:

- The standby database fails. The active database fails before the standby comes back up or before the standby has been synchronized with the active database.

- The active database fails. The standby database becomes ACTIVE, and the rest of the recovery process begins. (See "Recovering from a failure of the active database".) The new active database fails before the new standby database is fully synchronized with it.

In these scenarios, the subscribers may have had more changes applied than the standby database.

In this case, you could potentially perform one of the following options:

- Recover the active database and duplicate a new standby database

- Recover the standby database to be the new active master

- Restore the active master from a backup

Recover the active database and duplicate a new standby database

1. Connect to the failed active database. This triggers recovery from the local transaction logs. If you are replicating a read-only cache group, the autorefresh state is automatically set to PAUSED.

Note:
If this fails, perform the steps listed in "Restore the active master from a backup.".

2. Verify that the replication agent for the failed active database has restarted. If it has not restarted, then start the replication agent. See "Starting and stopping the replication agents".

3. Call ttRepStateSet('ACTIVE') on the newly recovered database. If you are replicating a read-only cache group, this action automatically causes the autorefresh state to change from PAUSED to ON for this database.

4. Verify that the cache agent for the failed database has restarted. If it has not restarted, then start the cache agent.

5. Duplicate the active database to the standby database. You can use either the ttRepAdmin -duplicate utility or the ttRepDuplicateEx C function to duplicate a database. Use the -keepCG command line option with ttRepAdmin to preserve the cache group. See "Duplicating a database".

6. Set up the replication agent policy on the standby database and start the replication agent. See "Starting and stopping the replication agents".

7. Wait for the standby database to enter the STANDBY state. Use the ttRepStateGet built-in procedure to check the state.

8. Start the cache agent for on the standby database using the ttCacheStart built-in procedure or the ttAdmin -cacheStart utility.

9. Duplicate all of the subscribers from the standby database. See "Duplicating a master database to a subscriber". Use the -noKeepCG command line option with ttRepAdmin in order to convert the cache group to regular TimesTen tables on the subscribers.

10. Set up the replication agent policy on the subscribers and start the agent on each of the subscriber databases. See "Starting and stopping the replication agents".

Recover the standby database to be the new active master

1. Connect to the failed standby master database. This triggers recovery from the local transaction logs. If you are replicating a read-only cache group, the autorefresh state is automatically set to PAUSED.

Note:
If this fails, perform the steps listed in "Restore the active master from a backup.".

2. If the replication agent for the failed standby master has automatically restarted, stop the replication agent. See "Starting and stopping the replication agents".

3. If the cache agent has automatically restarted, stop the cache agent.

4. Drop the replication configuration using the DROP ACTIVE STANDBY PAIR statement.

5. Drop and re-create all cache groups using the DROP CACHE GROUP and CREATE CACHE GROUP statements.

6. Re-create the replication configuration using the CREATE ACTIVE STANDBY PAIR statement.

7. Call ttRepStateSet('ACTIVE') on the master database, giving it the ACTIVE role. If you are replicating a read-only cache group, this action automatically causes the autorefresh state to change from PAUSED to ON for this database.

8. Set up the replication agent policy and start the replication agent on the new active database. See "Starting and stopping the replication agents".

9. Start the cache agent on the new active database.

10. Duplicate the active database to the standby database. You can use either the ttRepAdmin -duplicate utility or the ttRepDuplicateEx C function to duplicate a database. Use the -keepCG command line option with ttRepAdmin to preserve the cache group. See "Duplicating a database".

11. Set up the replication agent policy on the standby database and start the replication agent on the new standby database. See "Starting and stopping the replication agents".

12. Wait for the standby database to enter the STANDBY state. Use the ttRepStateGet built-in procedure to check the state.

13. Start the cache agent for the standby database using the ttCacheStart built-in procedure or the ttAdmin -cacheStart utility.

14. Duplicate all of the subscribers from the standby database. See "Duplicating a master database to a subscriber". Use the -noKeepCG command line option with ttRepAdmin in order to convert the cache group to regular TimesTen tables on the subscribers.

15. Set up the replication agent policy on the subscribers and start the agent on each of the subscriber databases. See "Starting and stopping the replication agents".

Restore the active master from a backup

If both the active and standby masters fail and neither comes up and you have a backup, then perform the following:

1. Restore the active master from a backup, as described in "Backing up and restoring a database with cache groups" in the Oracle TimesTen Application-Tier Database Cache User's Guide.

2. Drop the replication configuration using the DROP ACTIVE STANDBY PAIR statement.

3. Drop and re-create all AWT cache groups using the DROP CACHE GROUP and CREATE CACHE GROUP statements.

4. Start the replication agent and the cache agent, since the cache agent needs to be active to refresh any read-only cache groups and both must be active in order to load the AWT cache groups.

5. Refresh all read-only cache groups using the REFRESH CACHE GROUP statement to upload most current committed data from the cached Oracle database tables. Use the REFRESH CACHE GROUP ... PARALLEL n clause to concurrently load these cache groups over multiple threads.

6. Load all AWT cache groups using the LOAD CACHE GROUP statement to begin the autorefresh process. Use the LOAD CACHE GROUP ... PARALLEL n clause to concurrently load these cache groups over multiple threads.

7. Stop both the replication agent and the cache agent in preparation to re-create the active standby pair.

8. Re-create the replication configuration using the CREATE ACTIVE STANDBY PAIR statement.

9. Call ttRepStateSet('ACTIVE') on the active master database, giving it the ACTIVE role. If you are replicating a read-only cache group, this action automatically causes the autorefresh state to change from PAUSED to ON for this database.

10. Set up the replication agent policy and start the replication agent on the active database. See "Starting and stopping the replication agents".

11. Start the cache agent on the active database.

12. Duplicate the active database to the standby database. You can use either the ttRepAdmin -duplicate utility or the ttRepDuplicateEx C function to duplicate a database. Use the -keepCG command line option with ttRepAdmin to preserve the cache group. See "Duplicating a database".

13. Set up the replication agent policy on the standby database and start the replication agent on the new standby database. See "Starting and stopping the replication agents".

14. Wait for the standby database to enter the STANDBY state. Use the ttRepStateGet built-in procedure to check the state.

15. Start the cache agent for the standby database using the ttCacheStart built-in procedure or the ttAdmin -cacheStart utility.

16. Duplicate all of the subscribers from the standby database. See "Duplicating a master database to a subscriber". Use the -noKeepCG command line option with ttRepAdmin in order to convert the cache group to regular TimesTen tables on the subscribers.

17. Set up the replication agent policy on the subscribers and start the agent on each of the subscriber databases. See "Starting and stopping the replication agents".

Recovering from the failure of a subscriber database

If a subscriber database fails, then you can recover it by one of the following methods:

- Connect to the failed subscriber. This triggers recovery from the local transaction logs. Start the replication agent and let the subscriber catch up.

- Duplicate the subscriber from the standby database. You can use either the ttRepAdmin -duplicate utility or the ttRepDuplicateEx C function to duplicate a database. Use the -noKeepCG command line option with ttRepAdmin in order to convert the cache group to normal TimesTen tables on the subscriber.

If the standby database is down or in recovery, then duplicate the subscriber from the active database.

After the subscriber database has been recovered, then set up the replication agent policy and start the replication agent. See "Starting and stopping the replication agents".

Reversing the roles of the active and standby databases

To change the role of the active database to standby and vice versa:

1. Pause any applications that are generating updates on the current active database.

2. Call ttRepSubscriberWait on the active database, with the DSN and host of the current standby database as input parameters. It must return success (<00>). This ensures that all updates have been transmitted to the current standby database.

3. Stop the replication agent on the current active database. See "Starting and stopping the replication agents".

4. If global cache groups are not present, stop the cache agent on the current active database. When global cache groups are present, set the autorefresh state to PAUSED.

5. Call ttRepDeactivate on the current active database. This puts the database in the IDLE state. If you are replicating a read-only cache group, this action automatically causes the autorefresh state to change from ON to PAUSED for this database.

6. Call ttRepStateSet('ACTIVE') on the current standby database. This database now acts as the active database in the active standby pair. If you are replicating a read-only cache group, this automatically causes the autorefresh state to change from PAUSED to ON for this database.

7. Start the replication agent on the former master database.

8. Configure the replication agent policy as needed and start the replication agent on the former active database. Use the ttRepStateGet built-in procedure to determine when the database's state has changed from IDLE to STANDBY. The database now acts as the standby database in the active standby pair.

9. Start the cache agent on the former active database if it is not already running.

10. Resume any applications that were paused in Step 1.

Detecting dual active databases

See "Detection of dual active databases". There is no difference for active standby pairs that replicate cache groups.

Using a disaster recovery subscriber in an active standby pair

TimesTen active standby pair replication provides high availability by allowing for fast switching between databases within a data center. This includes the ability to automatically change which database propagates changes to an Oracle database using AWT cache groups. However, for additional high availability across data centers, you may require the ability to recover from a failure of an entire site, which can include a failure of both TimesTen master databases in the active standby pair as well as the Oracle database used for the cache groups.

You can recover from a complete site failure by creating a special disaster recovery read-only subscriber as part of the active standby pair replication scheme. The standby database sends updates to cache group tables on the read-only subscriber. This special subscriber is located at a remote disaster recovery site and can propagate updates to a second Oracle database, also located at the disaster recovery site. The disaster recovery subscriber can take over as the active in a new active standby pair at the disaster recovery site if the primary site suffers a complete failure. Any applications may then connect to the disaster recovery site and continue operating, with minimal interruption of service.

Requirements for using a disaster recovery subscriber with an active standby pair

To use a disaster recovery subscriber, you must:

- Use an active standby pair configuration with AWT cache groups at the primary site. The active standby pair can also include read-only cache groups in the replication scheme. The read-only cache groups are converted to regular tables on the disaster recovery subscriber. The AWT cache group tables remain AWT cache group tables on the disaster recovery subscriber.

- Have a continuous WAN connection from the primary site to the disaster recovery site. This connection should have at least enough bandwidth to guarantee that the normal volume of transactions can be replicated to the disaster recovery subscriber at a reasonable pace.

- Configure an Oracle database at the disaster recovery site to include tables with the same schema as the database at the primary site. Note that this database is intended only for capturing the replicated updates from the primary site, and if any data exists in tables written to by the cache groups when the disaster recovery subscriber is created, that data is deleted.

- Have the same cache group administrator user ID and password at both the primary and the disaster recovery site.

Though it is not absolutely required, you should have a second TimesTen database configured at the disaster recovery site. This database can take on the role of a standby database, in the event that the disaster recovery subscriber is promoted to an active database after the primary site fails.

Rolling out a disaster recovery subscriber

To create a disaster recovery subscriber, follow these steps:

1. Create an active standby pair with AWT cache groups at the primary site. The active standby pair can also include read-only cache groups. The read-only cache groups are converted to regular tables when the disaster recovery subscriber is rolled out.

2. Create the disaster recovery subscriber at the disaster recovery site using the ttRepAdmin utility with the -duplicate and -initCacheDR options. You must also specify the cache group administrator and password for the Oracle database at the disaster recovery site using the -cacheUid and -cachePwd options.
If your database includes multiple cache groups, you may improve the efficiency of the duplicate operation by using the -nThreads option to specify the number of threads that are spawned to flush the cache groups in parallel. Each thread flushes an entire cache group to the Oracle database and then moves on to the next cache group, if any remain to be flushed. If a value is not specified for -nThreads, only one flushing thread is spawned.

For example, duplicate the standby database mast2, on the system with the host name primary and the cache user ID system and password manager, to the disaster recovery subscriber drsub, and using two cache group flushing threads. ttRepAdmin prompts for the values of -uid, -pwd, -cacheUid and -cachePwd.

ttRepAdmin -duplicate -from mast2 -host primary -initCacheDR -nThreads 2
-connStr "DSN=drsub;UID=;PWD=;"

If you use the ttRepDuplicateEx function in C, you must set the TT_REPDUP_INITCACHEDR flag in ttRepDuplicateExArg.flags and may optionally specify a value for ttRepDuplicateExArg.nThreads4InitDR:

int                 rc;
ttUtilHandle        utilHandle;
ttRepDuplicateExArg arg;
memset( &arg, 0, sizeof( arg ) );
arg.size = sizeof( ttRepDuplicateExArg );
arg.flags = TT_REPDUP_INITCACHEDR;
arg.nThreads4InitDR = 2;
arg.uid="ttuser"
arg.pwd="ttuser"
arg.cacheuid = "system";
arg.cachepwd = "manager";
arg.localHost = "disaster";
rc = ttRepDuplicateEx( utilHandle, "DSN=drsub",
"mast2", "primary", &arg );

After the subscriber is duplicated, TimesTen automatically configures the replication scheme that propagates updates from the AWT cache groups to the Oracle database, truncates the tables in the Oracle database that correspond to the cache groups in TimesTen, and then flushes all of the data in the cache groups to the Oracle database.

3. If you want to set the failure threshold for the disaster recovery subscriber, call the ttCacheAWTThresholdSet built-in procedure and specify the number of transaction log files that can accumulate before the disaster recovery subscriber is considered either dead or too far behind to catch up.
If one or both master databases had a failure threshold configured before the disaster recovery subscriber was created, then the disaster recovery subscriber inherits the failure threshold value when it is created with the ttRepAdmin -duplicate -initCacheDR command. If the master databases have different failure thresholds, then the higher value is used for the disaster recovery subscriber.

For more information about the failure threshold, see "Setting the transaction log failure threshold".

4. Start the replication agent for the disaster recovery subscriber using the ttRepStart built-in procedure or the ttAdmin utility with the -repstart option. For example:

ttAdmin -repstart drsub

Updates are now replicated from the standby database to the disaster recovery subscriber, which then propagates the updates to the Oracle database at the disaster recovery site.

Switching over to the disaster recovery site

When the primary site has failed, you can switch over to the disaster recovery site in one of two ways. If your goal is to minimize risk of data loss at the disaster recovery site, you may roll out a new active standby pair using the disaster recovery subscriber as the active database. If the goal is to absolutely minimize the downtime of your applications, at the risk of data loss if the disaster recovery database later fails, you may instead choose to drop the replication scheme from the disaster recovery subscriber and use it as a single non-replicating database. You may deploy an active standby pair at the disaster recovery site later.

Creating a new active standby pair after switching to the disaster recovery site

1. Any read-only applications may be redirected to the disaster recovery subscriber immediately. Redirecting applications that make updates to the database must wait until Step 7.

2. Ensure that all of the recent updates to the cache groups have been propagated to the Oracle database using the ttRepSubscriberWait built-in procedure or the ttRepAdmin command with the -wait option.

Command> call ttRepSubscriberWait( null, null, '_ORACLE', null, 600 );

It must return success (<00>). If ttRepSubscriberWait returns 0x01, indicating a timeout, investigate to determine why the cache groups are not finished propagating before continuing to Step 3.

3. Stop the replication agent on the disaster recovery subscriber using the ttRepStop built-in procedure or the ttAdmin command with the -repstop option. For example, to stop the replication agent for the subscriber drsub, use:

Command> call ttRepStop;

4. Drop the active standby pair replication scheme on the subscriber using the DROP ACTIVE STANDBY PAIR statement. For example:

Command> DROP ACTIVE STANDBY PAIR;

5. If there are tables on the disaster recovery subscriber that were converted from read-only cache group tables on the active database, drop the tables on the disaster recovery subscriber.

6. Create the read-only cache groups on the disaster recovery subscriber. Ensure that the autorefresh state is set to PAUSED.

7. Create a new active standby pair replication scheme using the CREATE ACTIVE STANDBY PAIR statement, specifying the disaster recovery subscriber as the active database. For example, to create a new active standby pair with the former subscriber drsub as the active and the new database drstandby as the standby, and using the return twosafe return service, use:

Command> CREATE ACTIVE STANDBY PAIR drsub, drstandby RETURN TWOSAFE;

8. Set the new active standby database to the ACTIVE state using the ttRepStateSet built-in procedure. For example, on the database drsub in this example, call:

Command> call ttRepStateSet( 'ACTIVE' );

9. Any applications which must write to the TimesTen database may now be redirected to the new active database.

10. If you are replicating a read-only cache group, load the cache group using the LOAD CACHE GROUP statement to begin the autorefresh process. You may also load the cache group if you are replicating an AWT cache group, although it is not required.

11. Duplicate the active database to the standby database. You can use either the ttRepAdmin -duplicate utility or the ttRepDuplicateEx C function to duplicate a database. Use the -keepCG command line option with ttRepAdmin to preserve the cache group. See "Duplicating a database".

12. Set up the replication agent policy on the standby database and start the replication agent. See "Starting and stopping the replication agents".

13. Wait for the standby database to enter the STANDBY state. Use the ttRepStateGet built-in procedure to check the state.

14. Start the cache agent for the standby database using the ttCacheStart built-in procedure or the ttAdmin -cacheStart utility.

15. Duplicate all of the subscribers from the standby database. See "Duplicating a master database to a subscriber". Use the -noKeepCG command line option with ttRepAdmin in order to convert the cache group to regular TimesTen tables on the subscribers.

16. Set up the replication agent policy on the subscribers and start the agent on each of the subscriber databases. See "Starting and stopping the replication agents".

Switching over to a single database

1. Any read-only applications may be redirected to the disaster recovery subscriber immediately. Redirecting applications that make updates to the database must wait until Step 5.

2. Stop the replication agent on the disaster recovery subscriber using the ttRepStop built-in procedure or the ttAdmin command with the -repstop option. For example, to stop the replication agent for the subscriber drsub, use:

Command> call ttRepStop;

3. Drop the active standby pair replication scheme on the subscriber using the DROP ACTIVE STANDBY PAIR statement. For example:

Command> DROP ACTIVE STANDBY PAIR;

4. If there are tables on the disaster recovery subscriber that were converted from read-only cache group tables on the active database, drop the tables on the disaster recovery subscriber.

5. Create the read-only cache groups on the disaster recovery subscriber.

6. Although there is no longer an active standby pair configured, AWT cache groups require the replication agent to be started. Start the replication agent on the database using the ttRepStart built-in procedure or the ttAdmin command with the -repstart option. For example, to start the replication agent for the database drsub, use:

Command> call ttRepStart;

7. Any applications which must write to a TimesTen database may now be redirected to the this database.

Note:
You may choose to roll out an active standby pair at the disaster recovery site at a later time. You may do this by following the steps in "Creating a new active standby pair after switching to the disaster recovery site", starting at Step 2 and skipping Step 4.

Returning to the original configuration at the primary site

When the primary site is usable again, you may want to move the working active standby pair from the disaster recovery site back to the primary site. You can do this with a minimal interruption of service by reversing the process that was used to create and switch over to the original disaster recovery site. Follow these steps:

1. Destroy original active database at the primary site, if necessary, using the ttDestroy utility. For example, to destroy a database called mast1, use:

ttDestroy mast1

2. Create a disaster recovery subscriber at the primary site, following the steps detailed in "Rolling out a disaster recovery subscriber". Use the original active database for the new disaster recovery subscriber.

3. Switch over to the new disaster recovery subscriber at primary site, as detailed in "Switching over to the disaster recovery site". Roll out the standby database as well.

4. Roll out a new disaster recovery subscriber at the disaster recovery site, as detailed in "Rolling out a disaster recovery subscriber".

7 Altering an Active Standby Pair

This chapter includes the following sections:

- Making DDL changes in an active standby pair

- Making other changes to an active standby pair

Making DDL changes in an active standby pair

The following sections describe how you can configure automatic replication of certain DDL statements. That is, when you execute a supported DDL statement on the active master, it is automatically replicated to all databases in the active standby pair replication scheme.

- Controlling replication of objects to all databases in an active standby pair

- DDL statements that can be automatically replicated

- Creating a new PL/SQL object in an existing active standby pair

- Restrictions on making DDL changes in an active standby pair

- Examples: Making DDL changes in an active standby pair

- Examples: Altering an active standby pair

Controlling replication of objects to all databases in an active standby pair

Use the DDLReplicationLevel and DDLReplicationAction connection attributes to control what objects that are created or dropped by DDL statements are replicated to the databases involved in an active standby pair replication scheme. For more information on connection attributes, see "Specifying Data Source Names to identify TimesTen databases" in the Oracle TimesTen In-Memory Database Operations Guide

The DDLReplicationLevel connection attribute controls what DDL statements are replicated.

- DDLReplicationLevel=1. CREATE or DROP statements for tables, indexes, or synonyms are not replicated to the standby database. However, you can add or drop columns to or from a replicated table, and those actions are replicated to the standby database.

- DDLReplicationLevel=2 (the default) enables replication of creating and dropping of tables, indexes, and synonyms.
To include tables in the replication scheme, the DDLReplicationAction connection attribute must be set to 'INCLUDE' (the default) before creating the table. If DDLReplicationAction='EXCLUDE', then the table is not included in the replication scheme. If the table is excluded from the replication scheme, then the DDL statements for creating and dropping tables are replicated to the standby master; however, any DML statements executed on the table are not replicated.

Note:
You may want to exclude a table from a replication scheme if:

- You want to create a table in the replication scheme without either a primary key or a unique index on non-nullable columns.

- You want to create a temporary table where the data is only used locally and you do not want to replicate updates for this table.

To add an existing table to an active standby pair, use the ALTER ACTIVE STANDBY PAIR INCLUDE TABLE statement. The table must be empty.

However, you cannot alter a table to add a NOT NULL column to a table that is part of a replication scheme with the ALTER TABLE ... ADD COLUMN NOT NULL DEFAULT statement. You must remove the table from the replication scheme first before you can add a NOT NULL column to it.

- DDLReplicationLevel=3 enables the following:

- Replication to all databases in the replication scheme of the same objects that are replicated when DDLReplicationLevel=2.

- Replication of creating and dropping of views to all databases in the replication scheme.

- Replication of creating and dropping of sequences to all databases in the replication scheme, as long as DDLReplicationAction='INCLUDE' (the default) before creation. If DDLReplicationAction='EXCLUDE', then the sequence is not included in the replication scheme. If the sequence is excluded from the replication scheme, then the DDL statements for creating and dropping sequences are replicated to the standby master; however, each sequence on the active master and standby master are separate objects.

- Replication of the results to the standby master when you set the cache administration user name and password on the active master with the ttCacheUidPwdSet built-in procedure. You do not need to stop and restart the cache agent or replication agent in order to execute the ttCacheUidPwdSet built-in procedure on the active master. See "Changing user names or passwords used by replication" for more details.

- With this level, you can alter a table to add a NOT NULL column to a table that is part of a replication scheme with the ALTER TABLE ... ADD COLUMN NOT NULL DEFAULT statement.

You can set the DDLReplicationLevel attribute as part of the connection string or after the connection starts with the ALTER SESSION statement:

ALTER SESSION SET DDL_REPLICATION_LEVEL=3;

You can set the DDLReplicationAction attribute as part of the connection string or after the connection starts with the ALTER SESSION statement:

ALTER SESSION SET ddl_replication_action='EXCLUDE';

For more information, see "ALTER SESSION" and "ALTER ACTIVE STANDBY PAIR" in the Oracle TimesTen In-Memory Database SQL Reference.

Note:
When DDLCommitBehavior=0 (the default), DDL operations are automatically committed. When RETURN TWOSAFE has been specified, errors and timeouts may occur as described in "RETURN TWOSAFE". If a RETURN TWOSAFE timeout occurs, the DDL transaction is committed locally regardless of the LOCAL COMMIT ACTION that has been specified.

DDL statements that can be automatically replicated

You can execute the following DDL statements in an active standby pair without stopping the replication agent. In addition, these statements are replicated to all databases in the replication scheme. The following statements are automatically replicated when DDLReplicationLevel is 2 or 3 (the default is 2):

- Create, alter, or drop a user with the CREATE USER, ALTER USER, or DROP USER statements.

- Grant or revoke privileges from a user with the GRANT or REVOKE statements.

- Alter a table to add or drop a column with the ALTER TABLE ... ADD COLUMN or ALTER TABLE ... DROP COLUMN statements. These are the only ALTER TABLE clauses that are replicated. However, when DDLReplicationLevel=2, you cannot alter a table to add a NOT NULL column to a table that is part of a replication scheme with the ALTER TABLE ... ADD COLUMN NOT NULL DEFAULT statement. You can execute this statement if DDLReplicationLevel=3.

- Create or drop a table, including global temporary tables with the CREATE TABLE or DROP TABLE statements. The new table is also included in the active standby pair.

- Create or drop a synonym with the CREATE SYNONYM or DROP SYNONYM statements.

- Create or drop an index with the CREATE INDEX or DROP INDEX statements.

You can perform the following tasks in an active standby pair without stopping the replication agent. In addition, these statements are replicated to all databases in the replication scheme. The following statements are automatically replicated when DDLReplicationLevel is set to 3:

- Create or drop a view with the CREATE VIEW or DROP VIEW statements.

- Create or drop a sequence with the CREATE SEQUENCE or DROP SEQUENCE statements. These statements are automatically replicated to all databases in the replication scheme and included in the active standby pair when the DDLReplicationAction connection attribute is set to INCLUDE (the default) before creating the sequence; the sequence is not included in the replication scheme if the DDLReplicationAction connection attribute is set to EXCLUDE.

You do not have to stop the cache agent or replication agent when you set the user name and password for the cache administration user on the active master with the ttCacheUidPwdSet built-in procedure. When DDLReplicationLevel=3, then this information is automatically replicated to the standby master. See "Changing user names or passwords used by replication" for more information.

You can perform the following tasks in an active standby pair only after stopping the replication agents. These statements are not replicated to the standby master, so you must ensure that the changes are propagated to the standby master and any subscribers by either performing a duplicate or executing these statements on all nodes in the replication scheme after the replication agents are stopped. After execution, restart the replication agents on all nodes.

- The DDL statements for creating, dropping, or altering a materialized view.

- Changing the autorefresh mode or interval using the ALTER CACHE GROUP ... SET AUTOREFRESH MODE or ALTER CACHE GROUP ... SET AUTOREFRESH INTERVAL statements.

You can perform the following tasks in an active standby pair without stopping the replication agent. However, these statements are not replicated to the standby master, so you must ensure that the changes are propagated to the standby master and any subscribers by either performing a duplicate or executing these statements on all nodes in the replication scheme.

- Changing the autorefresh state of a cache group using the ALTER CACHE GROUP ... SET AUTOREFRESH STATE statement. However, you cannot set a cache group autorefresh state to OFF on the active master.

- Create or drop a PL/SQL function, PL/SQL procedure, PL/SQL package, or PL/SQL package body. You do not need to stop the replication agents for these objects. See "Creating a new PL/SQL object in an existing active standby pair" for more information on PL/SQL objects.

- Any other DDL statements that are not replicated (except for materialized views).

Creating a new PL/SQL object in an existing active standby pair

To add a new PL/SQL procedure, package, package body or function to an existing active standby pair, complete these tasks:

1. Create the PL/SQL object on the active database. The CREATE statement is not replicated to the standby database.

2. Create the PL/SQL object on the standby database and any subscribers.

3. Grant privileges to the new PL/SQL object on the active database. The GRANT statement is replicated to the standby database and any subscribers.

Restrictions on making DDL changes in an active standby pair

When DDLReplicationLevel=2 or 3:

- CREATE TABLE ... AS SELECT, ALTER TABLE ... ADD CONSTRAINT, ALTER TABLE ... ADD UNIQUE and ALTER TABLE ... MODIFY statements are not replicated.

- The CREATE INDEX statement is replicated only when the index is created on an empty table. To create a new index on populated tables, set DDLReplicationLevel to a value less than 2 and create the index manually on both the active and standby.

- These statements cannot be executed on the standby database when DDLReplicationLevel=2 or 3:

- CREATE USER, ALTER USER, DROP USER

- CREATE TABLE, DROP TABLE

- CREATE INDEX, DROP INDEX

- GRANT, REVOKE

- CREATE SYNONYM, DROP SYNONYM

When DDLReplicationLevel=3:

- CREATE SEQUENCE ... CYCLE statements are not replicated.

- These statements cannot be executed on the standby database when DDLReplicationLevel=3:

- CREATE INDEX, DROP INDEX

- CREATE SEQUENCE, DROP SEQUENCE when DDLReplicationAction='INCLUDE'.

Note:
However, you can create or drop a sequence on the standby master when DDLReplicationLevel=3 if DDLReplicationAction='EXCLUDE'.

Examples: Making DDL changes in an active standby pair

Example 7-1 Create a table and include it in the active standby pair

On the active database, set DDLReplicationLevel to 2 and DDLReplicationAction to 'INCLUDE'.

Command > ALTER SESSION SET ddl_replication_level=2;
Session altered.
Command > ALTER SESSION SET ddl_replication_action='INCLUDE';
Session altered.

Create a table. The table must have a primary key or index.

Command > CREATE TABLE tabinclude (col1 NUMBER NOT NULL PRIMARY KEY);
Table created.

Insert a row into tabinclude.

Command > INSERT INTO tabinclude VALUES (55);
1 row inserted.

On the standby database, verify that the INSERT statement has been replicated. This indicates that the tabinclude table has been included in the active standby pair.

Command > SELECT * FROM tabinclude;
< 55 >
1 row found.

Alternatively, use the ttIsql repschemes command to see what tables are included in the active standby pair.

Example 7-2 Create a table and add it to the active standby pair later

On the active database, set DDLReplicationLevel to 2 and DDLReplicationAction to 'EXCLUDE'.

Command> ALTER SESSION SET ddl_replication_level=2;
Session altered.
Command> ALTER SESSION SET ddl_replication_action='exclude';
Session altered.

Create a table that does not have a primary key or index. Try to include it in the active standby pair.

Command> CREATE TABLE newtab (a NUMBER NOT NULL);
Command> ALTER ACTIVE STANDBY PAIR INCLUDE TABLE newtab;
8000: No primary or unique index on non-nullable column found for replicated
table TERRY.NEWTAB
The command failed.

Create an index on the table. Include the table in the active standby pair.

Command> CREATE UNIQUE INDEX ixnewtab ON newtab(a);
Command> ALTER ACTIVE STANDBY PAIR INCLUDE TABLE newtab;

Insert a row into the table.

Command> INSERT INTO newtab VALUES (5);
1 row inserted.

On the standby database, verify that the row was inserted.

Command> SELECT * FROM newtab;
< 5 >
1 row found.

This example illustrates that a table does not need a primary key to be part of an active standby pair.

Example 7-3 CREATE INDEX is replicated

On the active database, set DDLReplicationLevel=2 and DDLReplicationAction='INCLUDE'.

Command> ALTER SESSION SET ddl_replication_level=2;
Session altered.
Command> ALTER SESSION SET ddl_replication_action='include';
Session altered.

Create a table with a primary key. The table is automatically included in the active standby pair.

Command> CREATE TABLE tab2 (a NUMBER NOT NULL, b NUMBER NOT NULL,
> PRIMARY KEY (a));

Create an index on the table.

Command> CREATE UNIQUE INDEX ixtab2 ON tab2 (b);

On the standby database, verify that the CREATE INDEX statement has been replicated.

Command> indexes;

Indexes on table TERRY.TAB2:
IXTAB2: unique T-tree index on columns:
B
TAB2: unique T-tree index on columns:
A
2 indexes found.

Indexes on table TERRY.NEWTAB:
NEWTAB: unique T-tree index on columns:
A
1 index found.

Indexes on table TERRY.TABINCLUDE:
TABINCLUDE: unique T-tree index on columns:
A
1 index found.
4 indexes found on 3 tables.

Example 7-4 CREATE SYNONYM is replicated

The DDLReplicationLevel is already set to 2, since it is the default. Create a synonym for tabinclude.

Command> CREATE SYNONYM syntabinclude FOR tabinclude;
Synonym created.

On the standby database, use the ttIsql synonyms command to verify that the CREATE SYNONYM statement has been replicated.

Command> synonyms;
TERRY.SYNTABINCLUDE
1 synonym found.

Making other changes to an active standby pair

You must stop the replication agent to make these changes to an active standby pair:

- Include or exclude a cache group.

- Add or drop a subscriber.

- Change values in the STORE clause.

- Change network operations (ADD ROUTE or DROP ROUTE clause).

To alter an active standby pair according to the preceding list, complete the following tasks:

1. Stop the replication agent on the active database. See "Starting and stopping the replication agents".

2. If the active standby pair includes cache groups, stop the cache agent on the active database.

3. Use the ALTER ACTIVE STANDBY PAIR statement to make changes to the replication scheme. See "Examples: Altering an active standby pair".

4. Start the replication agent on the active database. See "Starting and stopping the replication agents".

5. If the active standby pair includes cache groups, start the cache agent on the active database.

6. Destroy the standby database and the subscribers.

7. Duplicate the active database to the standby database. You can use either the ttRepAdmin -duplicate utility or the ttRepDuplicateEx C function to duplicate a database. If the active standby pair includes cache groups, use the -keepCG command line option with ttRepAdmin to preserve the cache group. See "Duplicating a database".

8. Set up the replication agent policy on the standby database and start the replication agent. See "Starting and stopping the replication agents".

9. Wait for the standby database to enter the STANDBY state. Use the ttRepStateGet built-in procedure to check the state.

10. If the active standby pair includes cache groups, start the cache agent for the standby database using the ttCacheStart built-in procedure or the ttAdmin -cacheStart utility.

11. Duplicate all of the subscribers from the standby database. See "Duplicating a master database to a subscriber". If the active standby pair includes cache groups, use the -noKeepCG command line option with ttRepAdmin in order to convert the cache group to regular TimesTen tables on the subscribers. See "Duplicating a database".

12. Set up the replication agent policy on the subscribers and start the agent on each of the subscriber databases. See "Starting and stopping the replication agents".

Examples: Altering an active standby pair

Example 7-5 Adding a subscriber to an active standby pair

Add a subscriber database to the active standby pair.

ALTER ACTIVE STANDBY PAIR
ADD SUBSCRIBER sub1;

Example 7-6 Dropping subscribers from an active standby pair

Drop subscriber databases from the active standby pair.

ALTER ACTIVE STANDBY PAIR
DROP SUBSCRIBER sub1
DROP SUBSCRIBER sub2;

Example 7-7 Changing the PORT and TIMEOUT settings for subscribers

Alter the PORT and TIMEOUT settings for subscribers sub1 and sub2.

ALTER ACTIVE STANDBY PAIR
ALTER STORE sub1 SET PORT 23000 TIMEOUT 180
ALTER STORE sub2 SET PORT 23000 TIMEOUT 180;

Example 7-8 Adding a cache group to an active standby pair

Add a cache group to the active standby pair.

ALTER ACTIVE STANDBY PAIR
INCLUDE CACHE GROUP cg0;

8 Using Oracle Clusterware to Manage Active Standby Pairs

Oracle Clusterware monitors and controls applications to provide high availability. The following sections describe how to use Oracle Clusterware to manage availability for a TimesTen active standby pair:

Note:
For more information about Oracle Clusterware, see Oracle Clusterware Administration and Deployment Guide in the Oracle Database documentation.

- Overview of how Oracle Clusterware can manage TimesTen

- Configuring Oracle Clusterware management with the cluster.oracle.ini file

- Creating and initializing a cluster

- Using Oracle Clusterware with a TimesTen cache grid

- Recovering from failures

- Clusterware management

- Monitoring cluster status

Overview of how Oracle Clusterware can manage TimesTen

Use Oracle Clusterware to manage only the following configurations:

- Active standby pair with or without read-only subscribers

- Active standby pair (with or without read-only subscribers) with AWT cache groups, read-only cache groups, and global cache groups

Figure 8-1 shows an active standby pair with one read-only subscriber in the same local network. The active database, the standby database and the read-only subscriber are on different nodes. There are two nodes that are not part of the active standby pair that are also running TimesTen. An application updates the active database. An application reads from the standby and the subscriber. All of the nodes are connected to shared storage.

Figure 8-1 Active standby pair with one subscriber

You can use Oracle Clusterware to start, monitor, and automatically fail over TimesTen databases and applications in response to node failures and other events. See "Clusterware management" and "Recovering from failures" for details.

Oracle Clusterware can be implemented at two levels of availability for TimesTen.

- The basic level of availability manages two master nodes and up to 127 read-only subscriber nodes in the cluster. The active standby pair is defined with local host names or IP addresses. If both master nodes fail, user intervention is necessary to migrate the active standby scheme to new hosts. When both master nodes fail, Oracle Clusterware notifies the user.

- The advanced level of availability uses virtual IP addresses for the active, standby, and read-only subscriber databases. Extra nodes can be included in the cluster that are not part of the initial active standby pair. If a failure occurs, the use of virtual IP addresses enables one of the extra nodes to take on the role of a failed node automatically.

Note:
If your applications connect to TimesTen in a client/server configuration, automatic client failover enables the client to reconnect automatically to the master database with the active role after a failure. See "Using automatic client failover for an active standby pair" and "TTC_FailoverPortRange" in the Oracle TimesTen In-Memory Database Reference.

The ttCWAdmin utility is used to administer TimesTen active standby pairs in a cluster that is managed by Oracle Clusterware. The configuration for each active standby pair is manually created in an initialization file called cluster.oracle.ini. The information in this file is used to create Oracle Clusterware resources. Resources are used to manage the TimesTen daemon, TimesTen databases, TimesTen processes, user applications, and virtual IP addresses. You can run the ttCWAdmin utility from any host in the cluster, as long as the cluster.oracle.ini file is reachable and readable from this host. For more information about the ttCWAdmin utility, see "ttCWAdmin" in Oracle TimesTen In-Memory Database Reference. For more information about the cluster.oracle.ini file, see "Configuring Oracle Clusterware management with the cluster.oracle.ini file".

Required privileges

See "ttCWAdmin" in Oracle TimesTen In-Memory Database Reference for information about the privileges required to run ttCWAdmin commands.

Hardware and software requirements

TimesTen does not support Clusterware on Windows platforms.

TimesTen supports Oracle Clusterware releases 11.2.0.2 and 11.2.0.3 with TimesTen active standby pair replication. See Oracle Clusterware Administration and Deployment Guide for network and storage requirements and information about Oracle Clusterware configuration files.

Oracle Clusterware and TimesTen should be installed in the same location on all nodes. The TimesTen instance administrator must belong to the same UNIX primary group as the Oracle Clusterware installation owner.

Note:
The /tmp directory contains essential TimesTen Oracle Clusterware directories. Their names have the prefix crsTT. Do not delete them.

All hosts should use Network Time Protocol (NTP) or a similar system so that clocks on the hosts remain within 250 milliseconds of each other. When adjusting the system clocks on any nodes to be synchronized with each other, do not set any clock backward in time.

Restricted commands and SQL statements

When you use Oracle Clusterware with TimesTen, the active standby pair replication scheme is created on the active master with the ttCWAdmin -create command and dropped with the ttCWAdmin -drop command. In between the ttCWAdmin -create and ttCWAdmin -drop commands, you cannot execute any of the following commands or SQL statements. However, you can perform these commands or SQL statements when you use the ttCWAdmin -beginAlterSchema and the ttCWAdmin -endAlterSchema commands, as described in "Changing the schema".

- Creating, altering, or dropping the active standby pair with the CREATE ACTIVE STANDBY PAIR, ALTER ACTIVE STANDBY PAIR, and DROP ACTIVE STANDBY PAIR SQL statements.

- Starting or stopping the replication agent with either the -repStart and -repStop options of the ttAdmin utility or the ttRepStart or ttRepStop built-in procedures.

- Starting or stopping the cache agent after the active standby pair has been created with either the -cacheStart and -cacheStop options of the ttAdmin utility or the ttCacheStart and ttCacheStop built-in procedures.

- Duplicating the database with the -duplicate option of the ttRepAdmin utility.

- Executing any built-in procedures for managing a cache grid when the active standby pair in a cluster is a member of a grid.

In addition, do not call ttDaemonAdmin -stop before calling ttCWAdmin -shutdown.

The TimesTen integration with Oracle Clusterware accomplishes these operations with the ttCWAdmin utility and the attributes specified in the cluster.oracle.ini file.

For more information about the built-ins and utilities, see Oracle TimesTen In-Memory Database Reference. For more information about the SQL statements, see Oracle TimesTen In-Memory Database SQL Reference.

Configuring Oracle Clusterware management with the cluster.oracle.ini file

The information in the cluster.oracle.ini file is used to create Oracle Clusterware resources that manage TimesTen databases, TimesTen processes, user applications, and virtual IP addresses. Create an initialization file called cluster.oracle.ini as a text file.

Note:
See Appendix A, "TimesTen Configuration Attributes for Oracle Clusterware" for details on all of the attributes that can be used in the cluster.oracle.ini file.

The ttCWAdmin -create command reads this file for configuration information, so the location of the text file must be reachable and readable by ttCWAdmin. The ttCWAdmin utility is used to administer TimesTen active standby pairs in a cluster that is managed by Oracle Clusterware.

It is recommended that you place this file in the TimesTen daemon home directory on the host for the active database. However, you can place this file in any directory or shared drive on the same host as where you run the ttCWAdmin -create command.

The default location for this file is in the install_dir/info directory. If you place this file in another location, identify the path of the location with the -ttclusterini option.

The entry name in the cluster.oracle.ini file must be the same as an existing system DSN in the sys.odbc.ini file. For example, [basicDSN] is the entry name in the cluster.oracle.ini file described in "Configuring basic availability". [basicDSN] must also be the DataStore and Data Source Name data store attributes in the sys.odbc.ini files on each host. For example, the sys.odbc.ini file for the basicDSN DSN on host1 might be:

[basicDSN]
DataStore=/path1/basicDSN
LogDir=/path1/log
DatabaseCharacterSet=AL32UTF8
ConnectionCharacterSet=AL32UTF8

The sys.odbc.ini file for basicDSN on host2 can have a different path, but all other attributes should be the same:

[basicDSN]
DataStore=/path2/basicDSN
LogDir=/path2/log
DatabaseCharacterSet=AL32UTF8
ConnectionCharacterSet=AL32UTF8

The following sections demonstrate sample configurations of the cluster.oracle.ini file:

- Configuring basic availability

- Configuring advanced availability

- Including cache groups in the active standby pair

- Including the active standby pair in a cache grid

- Implementing application failover

- Recovering from permanent failure of both master nodes

- Using the RepDDL attribute

Configuring basic availability

This example shows an active standby pair with no subscribers. The host for the active database is the first MasterHost defined (host1) and the standby database is the second MasterHost in the list (host2). Each host in the list is delimited by commas. You can include spaces for readability, if desired.

[basicDSN]
MasterHosts=host1,host2

The following is an example of a cluster.oracle.ini file for an active standby pair with one subscriber on host3:

[basicSubscriberDSN]
MasterHosts=host1,host2
SubscriberHosts=host3

Configuring advanced availability

Advanced availability involves configuring spare master or subscriber hosts that are idle until needed to replace master or subscriber hosts (used in the active standby pair replication scheme) that either shut down unexpectedly or experience an unrecoverable error.

As mentioned in "Configuring basic availability", the MasterHosts attribute in the cluster.oracle.ini file configures the hosts that are used as the master nodes. For an active standby pair replication scheme, you only need two master hosts. In the event of a failure, the host that did not fail becomes the active database (if not already the active database) and the failed host is recovered and becomes the standby master. However, if the failed host cannot be recovered and if you specified more than two hosts as master hosts in the cluster.oracle.ini file, then the next master host in the list can be instantiated to take the place of an unrecoverable master host.

For example, the following shows a configuration of several master hosts. The first two master hosts (host1 and host2) are used for the active and standby masters; the latter two master hosts (host3 and host4) can be used to take the place of either host1 or host2 if either encounter an unrecoverable failure.

MasterHosts=host1,host2,host3,host4

When you configure more than two multiple hosts, you should also configure two virtual IP (VIP) addresses used only by Oracle Clusterware resources that manage TimesTen resources. With these VIP addresses, TimesTen internal processes (those that manage replication) are isolated from any master host changes that may occur because of an unrecoverable host error.

Note:
The Oracle Clusterware resource that manage these VIP addresses (used in advanced availability) are created with the ttCWAdmin -createVIPs command, as described in "Create the Oracle Clusterware resources to manage virtual IP addresses".

These VIP addresses must be different from any other VIP addresses defined for Oracle Clusterware use or any VIP addresses that are to be used by user applications. Furthermore, if an application does use these VIP addresses, then the application may encounter errors when a master host fails (either recoverable or unrecoverable). These VIP addresses cannot be used by a user application as a method for client failover or as a method to isolate themselves if an active database and standby master switch.

Specify two VIP addresses in the MasterVIP parameter, one for each master host in the active standby pair replication scheme. The VIP addresses specified for the TimesTen cluster must be different from any VIP addresses already defined and used by Oracle Clusterware. In particular, the VIP addresses that are created during the Oracle Clusterware install cannot be used with TimesTen.

MasterVIP=192.168.1.1, 192.168.1.2

The following parameters are also associated with advanced availability in the cluster.oracle.ini file:

- SubscriberHosts, similar to MasterHosts lists the host names that can contain subscriber databases.

- SubscriberVIP, similar to MasterVIP, provides VIP addresses that can be used by TimesTen internally to manage a subscriber node.

- VIPInterface is the name of the public network adaptor.

- VIPNetMask defines the netmask of the virtual IP addresses.

In the following example, the hosts for the active database and the standby database are host1 and host2. The hosts available for instantiation in case of an unrecoverable error are host3 and host4. There are no subscriber nodes. VIPInterface is the name of the public network adaptor. VIPNetMask defines the netmask of the virtual IP addresses.

[advancedDSN]
MasterHosts=host1,host2,host3,host4
MasterVIP=192.168.1.1, 192.168.1.2
VIPInterface=eth0
VIPNetMask=255.255.255.0

The following example configures a single subscriber on host4. There is one extra host defined in SubscriberHosts that can be used for failover of the master databases and one extra node that can be used for failover of the subscriber database. MasterVIP and SubscriberVIP specify the virtual IP addresses defined for the master and subscriber hosts.

[advancedSubscriberDSN]
MasterHosts=host1,host2,host3
SubscriberHosts=host4,host5
MasterVIP=192.168.1.1, 192.168.1.2
SubscriberVIP=192.168.1.3
VIPInterface=eth0
VIPNetMask=255.255.255.0

Ensure that the extra master nodes:

- Have TimesTen installed

- Have the direct-linked application installed if this is part of the configuration. See "Implementing application failover".

Including cache groups in the active standby pair

If the active standby pair replicates one or more AWT or read-only cache groups, set the CacheConnect attribute to y.

This example specifies an active standby pair with one subscriber in an advanced availability configuration. The active standby pair replicates one or more cache groups.

[advancedCacheDSN]
MasterHosts=host1,host2,host3
SubscriberHosts=host4, host5
MasterVIP=192.168.1.1, 192.168.1.2
SubscriberVIP=192.168.1.3
VIPInterface=eth0
VIPNetMask=255.255.255.0
CacheConnect=y

Including the active standby pair in a cache grid

If the active standby pair is a member of a cache grid, assign port numbers for the active and standby databases by setting the GridPort attribute.

This example specifies an active standby pair with no subscribers in an advanced availability configuration. The active standby pair is a member of a cache grid.

[advancedGridDSN]
MasterHosts=host1,host2,host3
MasterVIP=192.168.1.1, 192.168.1.2
VIPInterface=eth0
VIPNetMask=255.255.255.0
CacheConnect=y
GridPort=16101, 16102

For more information about using Oracle Clusterware with a cache grid, see "Using Oracle Clusterware with a TimesTen cache grid".

Implementing application failover

TimesTen integration with Oracle Clusterware can facilitate the failover of a TimesTen application that is linked to any of the databases in the active standby pair. TimesTen can manage both direct-linked and client/server applications that are on the same host as Oracle Clusterware and TimesTen.

The required attributes in the cluster.oracle.ini file for failing over a TimesTen application are as follows:

- AppName - Name of the application to be managed by Oracle Clusterware

- AppStartCmd - Command line for starting the application

- AppStopCmd - Command line for stopping the application

- AppCheckCmd - Command line for executing an application that checks the status of the application specified by AppName

- AppType - Determines the database to which the application is linked. The possible values are Active, Standby, DualMaster, Subscriber (all) and Subscriber[index].

There are also several optional attributes that you can configure, such as AppFailureThreshold, DatabaseFailoverDelay, and AppScriptTimeout. All optional attributes (and their default values) are listed and described in Table A-3, "Optional attributes".

The TimesTen application monitor process uses the user-supplied script or program specified by AppCheckCmd to monitor the application. The script that checks the status of the application must be written to return 0 for success and a nonzero number for failure. When Oracle Clusterware detects a nonzero value, it takes action to recover the failed application.

This example shows advanced availability configured for an active standby pair with with no subscribers. The reader application is an application that queries the data in the standby database. AppStartCmd, AppStopCmd and AppCheckCmd can include arguments such as start, stop and check commands.

Note:
Do not use quotes in the values for AppStartCmd, AppStopCmd and AppCheckCmd.

[appDSN]
MasterHosts=host1,host2,host3,host4
MasterVIP=192.168.1.1, 192.168.1.2
VIPInterface=eth0
VIPNetMask=255.255.255.0
AppName=reader
AppType=Standby
AppStartCmd=/mycluster/reader/app_start.sh start
AppStopCmd=/mycluster/reader/app_stop.sh stop
AppCheckCmd=/mycluster/reader/app_check.sh check

You can configure failover for more than one application. Use AppName to name the application and provide values for AppType, AppStartCmd, AppStopCmd and AppCheckCmd immediately following the AppName attribute. You can include blank lines for readability. For example:

[app2DSN]
MasterHosts=host1,host2,host3,host4
MasterVIP=192.168.1.1, 192.168.1.2
VIPInterface=eth0
VIPNetMask=255.255.255.0

AppName=reader
AppType=Standby
AppStartCmd=/mycluster/reader/app_start.sh
AppStopCmd=/mycluster/reader/app_stop.sh
AppCheckCmd=/mycluster/reader/app_check.sh

AppName=update
AppType=Active
AppStartCmd=/mycluster/update/app2_start.sh
AppStopCmd=/mycluster/update/app2_stop.sh
AppCheckCmd=/mycluster/update/app2_check.sh

If you set AppType to DualMaster, the application starts on both the active and the standby hosts. The failure of the application on the active host causes the active database and all other applications on the host to fail over to the standby host. You can configure the failure interval, the number of restart attempts, and the uptime threshold by setting the AppFailureInterval, AppRestartAttempts and AppUptimeThreshold attributes. These attributes have default values. For example:

[appDualDSN]
MasterHosts=host1,host2,host3,host4
MasterVIP=192.168.1.1, 192.168.1.2
VIPInterface=eth0
VIPNetMask=255.255.255.0
AppName=update
AppType=DualMaster
AppStartCmd=/mycluster/update/app2_start.sh
AppStopCmd=/mycluster/update/app2_stop.sh
AppCheckCmd=/mycluster/update/app2_check.sh
AppRestartAttempts=5
AppUptimeThreshold=300
AppFailureInterval=30

Note:
For a full description of all configuration attributes, see Appendix A, "TimesTen Configuration Attributes for Oracle Clusterware".

Recovering from permanent failure of both master nodes

If both master nodes fail and then come back up, Oracle Clusterware can automatically recover the master databases. Automatic recovery of temporary dual failure requires the following:

- RETURN TWOSAFE is not specified for the active standby pair.

- AutoRecover is set to y.

- RepBackupDir specifies a directory on shared storage.

- RepBackupPeriod is set to a value greater than 0.

If both master nodes fail permanently, Oracle Clusterware can automatically recover the master databases to two new nodes if the following is true:

- Advanced availability is configured (virtual IP addresses and at least four hosts).

- The active standby pair does not replicate cache groups.

- A cache grid is not configured.

- RETURN TWOSAFE is not specified.

- AutoRecover is set to y.

- RepBackupDir specifies a directory on shared storage.

- RepBackupPeriod must be set to a value greater than 0.

TimesTen first performs a full backup of the active database and then performs incremental backups. You can specify the optional attribute RepFullBackupCycle to manage when TimesTen performs subsequent full backup. By default, TimesTen performs a full backup after every five incremental backups.

If RepBackupDir and RepBackupPeriod are configured for backups, TimesTen performs backups for any master database that becomes active. It does not delete backups that were performed for a database that used to be active and has become the standby unless the database becomes active again. Ensure that the shared storage has enough space for two complete database backups. The ttCWAdmin -restore command automatically chooses the correct backup files.

Incremental backups increase the amount of log records in the transaction log files. Ensure that the values of RepBackupPeriod and RepFullBackupCycle are small enough to prevent a large amount of log records in the transaction log file.

This example shows attribute settings for automatic recovery.

[autorecoveryDSN]
MasterHosts=host1,host2,host3,host4
MasterVIP=192.168.1.1, 192.168.1.2
VIPInterface=eth0
VIPNetMask=255.255.255.0
AutoRecover=y
RepBackupDir=/shared_drive/dsbackup
RepBackupPeriod=3600

If you have cache groups in the active standby pair or prefer to recover manually from failure of both master hosts, ensure that AutoRecover is set to n (the default). Manual recovery requires the following:

- RepBackupDir specifies a directory on shared storage

- RepBackupPeriod must be set to a value greater than 0

This example shows attribute settings for manual recovery. The default value for AutoRecover is n, so it is not included in the file.

[manrecoveryDSN]
MasterHosts=host1,host2,host3
MasterVIP=192.168.1.1, 192.168.1.2
VIPInterface=eth0
VIPNetMask=255.255.255.0
RepBackupDir=/shared_drive/dsbackup
RepBackupPeriod=3600

Using the RepDDL attribute

The RepDDL attribute represents the SQL statement that creates the active standby pair. The RepDDL attribute is optional. You can use it to exclude tables, cache groups and sequences from the active standby pair.

If you include RepDDL in the cluster.oracle.ini file, do not specify ReturnServiceAttribute, MasterStoreAttribute or SubscriberStoreAttribute in the cluster.oracle.ini file. Include those replication settings in the RepDDL attribute.

When you specify a value for RepDDL, use the <DSN> macro for the database file name prefix. Use the <MASTERHOST[1]> and <MASTERHOST[2]> macros to specify the master host names. TimesTen substitutes the correct values from the MasterHosts or MasterVIP attributes, depending on whether your configuration uses virtual IP addresses. Similarly, use the <SUBSCRIBERHOST[n]> macro to specify subscriber host names, where n is a number from 1 to the total number of SubscriberHosts attribute values or 1 to the total number of SubscriberVIP attribute values if virtual IP addresses are used.

Use the RepDDL attribute to exclude tables, cache groups, and sequences from the active standby pair:

[excludeDSN]
MasterHosts=host1,host2,host3,host4
SubscriberHosts=host5,host6
MasterVIP=192.168.1.1, 192.168.1.2
SubscriberVIP=192.168.1.3
VIPInterface=eth0
VIPNetMask=255.255.255.0
RepDDL=CREATE ACTIVE STANDBY PAIR \
<DSN> ON <MASTERHOST[1]>, <DSN> ON <MASTERHOST[2]>
SUBSCRIBER <DSN> ON <SUBSCRIBERHOST[1]>\
EXCLUDE TABLE pat.salaries, \
EXCLUDE CACHE GROUP terry.salupdate, \
EXCLUDE SEQUENCE ttuser.empcount

The replication agent transmitter obtains route information as follows, in order of priority:

1. From the ROUTE clause in the RepDDL setting, if a ROUTE clause is specified. Do not specify a ROUTE clause if you are configuring advanced availability.

2. From Oracle Clusterware, which provides the private host names and public host names of the local and remote hosts as well as the remote daemon port number. The private host name is preferred over the public host name. If the replication agent transmitter cannot connect to the IPC socket, it attempts to connect to the remote daemon using information that Oracle Clusterware maintains about the replication scheme.

3. From the active and standby hosts. If they fail, then the replication agent chooses the connection method based on host name.

This is an example of specifying the ROUTE clause in RepDDL:

[routeDSN]
MasterHosts=host1,host2,host3,host4
RepDDL=CREATE ACTIVE STANDBY PAIR \
<DSN> ON <MASTERHOST[1]>, <DSN> ON <MASTERHOST[2]>\
ROUTE MASTER <DSN> ON <MASTERHOST[1]>  SUBSCRIBER <DSN> ON <MASTERHOST[2]>\
MASTERIP "192.168.1.2" PRIORITY 1\
SUBSCRIBERIP "192.168.1.3" PRIORITY 1\
MASTERIP "10.0.0.1" PRIORITY 2\
SUBSCRIBERIP "10.0.0.2" PRIORITY 2\
MASTERIP "140.87.11.203" PRIORITY 3\
SUBSCRIBERIP "140.87.11.204" PRIORITY 3\
ROUTE MASTER <DSN> ON <MASTERHOST[2]>  SUBSCRIBER <DSN> ON <MASTERHOST[1]>\
MASTERIP "192.168.1.3" PRIORITY 1\
SUBSCRIBERIP "192.168.1.2" PRIORITY 1\
MASTERIP "10.0.0.2" PRIORITY 2\
SUBSCRIBERIP "10.0.0.1" PRIORITY 2\
MASTERIP "140.87.11.204" PRIORITY 3\
SUBSCRIBERIP "140.87.11.203" PRIORITY 3\

Creating and initializing a cluster

To create and initialize a cluster, perform these tasks:

- Install Oracle Clusterware

- Install TimesTen on each host

- Register the TimesTen cluster information

- Start the TimesTen cluster agent

- Create and populate a TimesTen database on one host

- Create system DSN files on other hosts

- Create a cluster.oracle.ini file

- Create the Oracle Clusterware resources to manage virtual IP addresses

- Create an active standby pair replication scheme

- Start the active standby pair and the applications

- Load cache groups

- Include more than one active standby pair in a cluster

- Configure an Oracle database as a disaster recovery subscriber

- Configure a read-only subscriber that is not managed by Oracle Clusterware

If you plan to have more than one active standby pair in the cluster, see "Include more than one active standby pair in a cluster".

If you want to configure an Oracle database as a remote disaster recovery subscriber, see "Configure an Oracle database as a disaster recovery subscriber".

If you want to set up a read-only subscriber that is not managed by Oracle Clusterware, see "Configure a read-only subscriber that is not managed by Oracle Clusterware".

Install Oracle Clusterware

Install Oracle Clusterware. By default, the installation occurs on all hosts concurrently. See Oracle Clusterware installation documentation for your platform.

Oracle Clusterware starts automatically after successful installation.

Note:
You can verify whether Oracle Clusterware is running on all hosts in the cluster by executing the following:

crsctl check crs -all

Install TimesTen on each host

Install TimesTen in the same location on each host in the cluster, including extra hosts. The instance name must be the same on each host. The user name of the instance administrator must be the same on all hosts. The TimesTen instance administrator must belong to the same UNIX primary group as the Oracle Clusterware installation owner.

The installer prompts you for values for the following, each of which are stored in the ttcrsagent.options file:

- The TCP/IP port number associated with the TimesTen cluster agent. The port number must be the same on all nodes of the cluster. If you do not provide a port number, then TimesTen adds six to the default TimesTen daemon port number to be the TCP/IP port number associated with the TimesTen cluster agent. Thus, the default daemon port number associated with the TimesTen cluster agent is 53398 for 32-bit systems and 53402 for 64-bit systems.

- The Oracle Clusterware location. The location must be the same on each host.

- The hosts included in the cluster, including spare hosts, with host names separated by commas. This list must be the same on each host.

The ttCWAdmin –init and ttCWAdmin –shutdown commands use the ttcrsagent.options file to initiate and shut down the TimesTen cluster. The ttcrsagent.options file is located in the TimesTen daemon home directory.

You should not manually alter the ttcrsagent.options file. Instead, use the ttmodinstall -crs command to create or modify the information in this file after the TimesTen cluster has been initiated. You can also use the -record and -batch options for setup.sh to perform identical installations on additional hosts.

The current home location of Oracle Clusterware is set in the CRS_HOME environment variable. In addition, the ttmodinstall -crs command shows the current location of the Oracle Clusterware home as part of the prompts.

Note:
For more information on the ttcrsagent.options file, see "Start the TimesTen cluster agent". For more information about ttmodinstall, see "ttmodinstall" in Oracle TimesTen In-Memory Database Reference.

The following example shows how the ttmodinstall -crs prompts for you to modify each item in the ttcrsagent.options file:

% ttmodinstall -crs

Cannot find instance_info file : /etc/TimesTen/instance_info

Would you like to modify the existing TimesTen Replication with Oracle
Clusterware configuration? [ no ] yes

This TimesTen instance is configured to use an Oracle Clusterware installation
located in : /mydir/oracle/crs/app/11.2.0/grid
Would you like to change this value? [ no ] no

The TimesTen Clusterware agent is configured to use port 54504
Would you like to change this value? [ no ] no

The TimesTen Clusterware agent is currently configured with these nodes :

node1
node2
node3
node4

Would you like to change these values? [ no ]

Overwrite the existing TimesTen Clusterware options file? [ no ] no

Register the TimesTen cluster information

TimesTen cluster information is stored in the Oracle Cluster Registry (OCR). As the root user, enter this command:

ttCWAdmin -ocrConfig

As long as Oracle Clusterware and TimesTen are installed on the hosts, this step never needs to be repeated.

Start the TimesTen cluster agent

Start a TimesTen cluster agent and TimesTen cluster daemon monitor on all hosts in the cluster by executing the ttCWAdmin -init command. You can execute this command on any host in the cluster that is defined in the ttcrsagent.options file.

For example:

ttCWAdmin -init

The ttCWAdmin -init command performs the following:

- Reads the ttcrsagent.options file and launches the TimesTen main daemon on each of the hosts defined in this file.

- Starts and registers the TimesTen cluster agent (ttCRSAgent) and the TimesTen cluster daemon monitor (ttCRSDaemon) on the all hosts in the cluster. There is one TimesTen cluster agent and one TimesTen cluster daemon monitor for the TimesTen installation on each host. When the TimesTen cluster agent has started, Oracle Clusterware begins monitoring the TimesTen daemon on each host and restarts a TimesTen daemon if it fails.

To start and register the TimesTen cluster agent (ttCRSAgent) and the TimesTen cluster daemon monitor (ttCRSDaemon) on specific hosts in the cluster, use the -hosts command to specify the desired hosts in the cluster to start.

ttCWAdmin -init -hosts "host1, host2"

Note:
You must stop the TimesTen cluster agent on the local host with the ttCWAdmin -shutdown before you run a ttDaemonAdmin -stop command; otherwise the cluster agent restarts the TimesTen daemon.

Create and populate a TimesTen database on one host

Create a database on the host where you intend the active database to reside. The DSN must be the same as the database file name.

Create schema objects (such as tables, AWT cache groups, and read-only cache groups) and populate with data as appropriate. However, before you create cache groups, you must first decide when to load the cache groups.

- For best performance, load the cache group tables from the Oracle database tables before the ttCWAdmin -create command. There is less performance overhead when cache groups are loaded with initial data before the duplicate is performed on the active master to create the standby master (and any subscribers).
For this option, perform the following:

1. Start the cache agent as follows:

Command> call ttCacheStart;

Note:
Since this is before the ttCWAdmin -start command, you can start the cache agent at this time. The ttCWAdmin -start command notes that the cache agent is already started and continues.

2. Use the LOAD CACHE GROUP statement to load the cache group tables from the Oracle database tables.

3. If using autorefresh cache groups, set the autorefresh state to pause with the ALTER CACHE GROUP SET AUTOREFRESH STATE PAUSED statement. The autorefresh state will be set to ON as part of the ttCWAdmin -start command.

The following example demonstrates how to create a read-only autorefresh cache group, load the data, and then set the autorefresh state to pause:

Command> call ttCacheStart;
Command> CREATE READONLY CACHE GROUP my_cg
AUTOREFRESH MODE INCREMENTAL INTERVAL 60 SECONDS
FROM t1 (c1 NUMBER(22) NOT NULL PRIMARY KEY, c2 DATE, c3 VARCHAR(30));

Command> LOAD CACHE GROUP my_cg COMMIT EVERY 100 ROWS PARALLEL 4;
Command> ALTER CACHE GROUP my_cg SET AUTOREFRESH STATE PAUSED;

- Alternatively, wait to load the cache group tables after the ttCWAdmin -start as described in "Load cache groups". The data will be replicated to the standby master and any subscribers.

Create system DSN files on other hosts

On all hosts that are to be included in the cluster, create the system DSN (sys.odbc.ini) files. The DataStore attribute and the Data Source Name must be the same as the entry name for the cluster.oracle.ini file. See "Configuring Oracle Clusterware management with the cluster.oracle.ini file" for information about the contents of the sys.odbc.ini files.

Create a cluster.oracle.ini file

Create a cluster.oracle.ini file as a text file. See "Configuring Oracle Clusterware management with the cluster.oracle.ini file" for details about its contents and acceptable locations for the file.

Create the Oracle Clusterware resources to manage virtual IP addresses

Advanced availability involves configuring spare master or subscriber hosts that are idle until needed to replace master or subscriber hosts (used in the active standby pair replication scheme) that either shut down unexpectedly or experience an unrecoverable error. This is an optional step that is only necessary if you decide to configure advanced availability.

If you are planning on providing additional master or subscriber hosts for advanced availability, then you need to configure virtual IP addresses (one for each master host and subscriber actively used in the active standby pair). See "Configuring advanced availability" for more details on how many virtual IP addresses should be created.

In this case, perform the following:

1. Designate (or create) new virtual IP addresses on the network that are to be used solely for managing multiple hosts in a TimesTen replication environment managed by Oracle Clusterware.

2. Configure these VIP addresses for use to manage multiple hosts for advanced availability in the cluster.oracle.ini file, as described in "Configuring advanced availability".

3. Create the Oracle Clusterware resources that manage these VIP addresses by executing the ttCWAdmin -createVIPs command as the root user on any host in the cluster.
For example:

ttCWAdmin -createVIPs -dsn myDSN

The VIP address names created by this command start with network_ followed by the TimesTen instance name, TimesTen instance administrator, and the DSN. Whereas, the VIP addresses created for use by Oracle Clusterware are prefixed with ora.

Note:
The ttCWAdmin -createVIPs command must be executed before the ttCWAdmin -create command. If you decide that you want to use VIP addresses for advanced availability after you have executed the ttCWAdmin -create command, you must perform the following:

1. Execute ttCWadmin -drop to drop the active standby pair replication scheme.

2. Add VIP addresses into cluster.oracle.ini file.

3. Execute ttCWadmin -createVIPs to create the resources to manage the VIP addresses.

4. Execute ttCWAdmin -create to create the active standby pair replication scheme managed by Oracle Clusterware.

Once created, the only way to drop the Oracle Clusterware resources that manage the VIP addresses is to execute the ttCWAdmin -dropVIPs command. Before you can drop the virtual IP addresses, you must first execute the ttCWAdmin -drop command.

The following is an example of how to drop the virtual IP addresses:

ttCWAdmin -dropVIPs -dsn myDSN

For an example of when to use the ttCWAdmin -dropVIPs command, see "Removing an active standby pair from a cluster".

Create an active standby pair replication scheme

Create an active standby pair replication scheme by executing the ttCWAdmin -create command on any host in the cluster.

Note:
The cluster.oracle.ini file contains the configuration needed to perform the ttCWAdmin -create command and so must reachable by the ttCWAdmin executable. See "Configuring Oracle Clusterware management with the cluster.oracle.ini file" for more details.

For example:

ttCWAdmin -create -dsn myDSN

The ttCWAdmin -create command prompts for the following:

- Prompts for the name of a TimesTen user with ADMIN privileges. If cache groups are being managed by Oracle Clusterware, enter the TimesTen cache manager user name.

- Prompts for the TimesTen password for the previously entered user name.

- If cache groups are being used, prompts for the password for the Oracle user that has the same name as the cache manager user. This password is provided in the OraclePWD connection attribute when the cache manager user connects.

- Prompts for a random string used to encrypt the above information.

If you want to specify the path and name of a file to be used as the cluster.oracle.ini file, use the -ttclusterini command.

ttCWAdmin -create -dsn myDSN -ttclusterini path/to/cluster/mycluster.ini

To drop the active standby pair, use the ttCWAdmin -drop command, as follows:

ttCWAdmin -drop -dsn myDSN

Note:
If your application connects to the TimesTen database using the virtual IP address, then this connection drops with the ttCWAdmin -drop command, since the virtual IP address is managed by Oracle Clusterware. However, if your application connects to the TimesTen database using the host name, the connection is not dropped.

For examples showing the sequence in which to use the ttCWAdmin -create and ttCWAdmin -drop commands, see "Managing active standby pairs in a cluster" and "Managing read-only subscribers in the active standby pair".

Start the active standby pair and the applications

Start the cluster with the active standby pair replication scheme by executing the ttCWAdmin -start command on any host. This starts the cache agent (if not already started) and replication agent on the active database, performs the duplicate to create the standby master (and any subscribers), and starts the cache agent and replication agent on the standby master (and any subscribers).

If you do not specify -noApp, the applications are also started. If you do specify -noApp, then you can start and stop the applications with the -startApps and -stopApps commands respectively.

For example:

ttCWAdmin -start -dsn myDSN

This command starts the following processes for the active standby pair:

- ttCRSMaster

- ttCRSActiveService

- ttCRSsubservice

- Monitor for application AppName

The following example starts the cache and replication agents, but does not start the applications because of the inclusion of the -noapp command:

ttCWAdmin -start -noapp -dsn myDSN

To start and stop applications, use the -startApps and -stopApps commands as shown below:

ttCWAdmin -startapps -dsn myDSN
...
ttCWAdmin -stopapps -dsn myDSN

To stop the cache agent and replication agent and disconnect the application from both databases, execute the ttCWAdmin -stop command.

ttCWAdmin -stop -dsn myDSN

Note:
If your application connects to the TimesTen database using a virtual IP address, then this connection drops with the ttCWAdmin -stop command, since the virtual IP address is managed by Oracle Clusterware. However, if your application connects to the TimesTen database using the host name, the connection is not dropped; however, replication to the standby master does not occur.

For examples showing the sequence in which to use the ttCWAdmin -start and ttCWAdmin -stop commands, see "Managing active standby pairs in a cluster" and "Managing read-only subscribers in the active standby pair".

Load cache groups

If the active standby pair includes cache groups and you have not already loaded the cache group (as described in "Create and populate a TimesTen database on one host"), use the LOAD CACHE GROUP statement to load the cache group tables from the Oracle database tables.

For more information on when to load cache groups, see "Create and populate a TimesTen database on one host".

Include more than one active standby pair in a cluster

If you want to use Oracle Clusterware to manage more than one active standby pair in a cluster, include additional configuration in the cluster.oracle.ini file. Oracle Clusterware can only manage more than one active standby pair in a cluster if all TimesTen databases are a part of the same TimesTen instance on a single host.

For example, the following cluster.oracle.ini file contains configuration information for two active standby pair replication schemes on the same host:

Note:
For details on configuration attributes in the cluster.oracle.ini file, see Appendix A, "TimesTen Configuration Attributes for Oracle Clusterware".

[advancedSubscriberDSN]
MasterHosts=host1,host2,host3
SubscriberHosts=host4, host5
MasterVIP=192.168.1.1, 192.168.1.2
SubscriberVIP=192.168.1.3
VIPInterface=eth0
VIPNetMask=255.255.255.0

[advSub2DSN]
MasterHosts=host1,host2,host3
SubscriberHosts=host4, host5
MasterVIP=192.168.1.4, 192.168.1.5
SubscriberVIP=192.168.1.6
VIPInterface=eth0
VIPNetMask=255.255.255.0

Perform these tasks for additional replication schemes:

1. Create and populate the databases.

2. Create the virtual IP addresses. Use the ttCWAdmin -createVIPs command.

3. Create the active standby pair replication scheme. Use the ttCWAdmin -create command.

4. Start the active standby pair. Use the ttCWAdmin -start command.

Configure an Oracle database as a disaster recovery subscriber

You can create an active standby pair on the primary site with an Oracle database as a remote disaster recovery subscriber. See "Using a disaster recovery subscriber in an active standby pair". Oracle Clusterware manages the active standby pair, but does not manage the disaster recovery subscriber. The user must perform a switchover if the primary site fails.

To use Oracle Clusterware to manage an active standby pair that has a remote disaster recovery subscriber, perform these tasks:

1. Use the RepDDL or RemoteSubscriberHosts Clusterware attribute to provide information about the remote disaster recovery subscriber. For example:

[advancedDRsubDSN]
MasterHosts=host1,host2,host3
SubscriberHosts=host4, host5
RemoteSubscriberHosts=host6
MasterVIP=192.168.1.1, 192.168.1.2
SubscriberVIP=192.168.1.3
VIPInterface=eth0
VIPNetMask=255.255.255.0
CacheConnect=y

2. Use ttCWAdmin -create to create the active standby pair replication scheme on the primary site. This does not create the disaster recovery subscriber.

3. Use ttCWAdmin -start to start the active standby pair replication scheme.

4. Load the cache groups that are replicated by the active standby pair.

5. Set up the disaster recovery subscriber using the procedure in "Rolling out a disaster recovery subscriber".

Configure a read-only subscriber that is not managed by Oracle Clusterware

You can include a read-only TimesTen subscriber database that is not managed by Oracle Clusterware. Perform these tasks:

1. Include the RemoteSubscriberHosts Clusterware attribute in the cluster.oracle.ini file. For example:

[advancedROsubDSN]
MasterHosts=host1,host2,host3
RemoteSubscriberHosts=host6
MasterVIP=192.168.1.1, 192.168.1.2
SubscriberVIP=192.168.1.3
VIPInterface=eth0
VIPNetMask=255.255.255.0

2. Use ttCWAdmin -create to create the active standby pair replication scheme on the primary site.

3. Use ttCWAdmin -start to start the active standby pair replication scheme. This does not create the read-only subscriber.

4. Use the ttRepStateGet built-in procedure to verify that the state of the standby database is STANDBY.

5. On the subscriber host, use ttRepAdmin -duplicate option to duplicate the standby database to the read-only subscriber. See "Duplicating a database".

6. Start the replication agent on the subscriber host.

To add or drop a read-only subscriber to or from an existing configuration, see "Adding or dropping a read-only subscriber not managed by Oracle Clusterware".

To rebuild a read-only subscriber, see "Rebuilding a read-only subscriber not managed by Oracle Clusterware".

Using Oracle Clusterware with a TimesTen cache grid

You can use the TimesTen implementation of Oracle Clusterware to manage a cache grid when each grid member is an active standby pair. TimesTen does not support using Oracle Clusterware to manage standalone grid members.

This section includes:

- Creating and initializing a cluster of cache grid members

- Failure and recovery for active standby pair grid members

- Making schema changes to active standby pairs in a grid

Creating and initializing a cluster of cache grid members

See "Install TimesTen on each host" for installation requirements. In addition, each grid member must have a DSN that is unique within the cache grid.

Perform the tasks described in "Creating and initializing a cluster" for each grid member. Include the GridPort Clusterware attribute in the cluster.oracle.ini file as described in "Including the active standby pair in a cache grid". Ensure that the specified port numbers are not in use.

The ttCWAdmin -start command automatically attaches a grid member to the cache grid. The ttCWAdmin -stop command automatically detaches a grid member from the cache grid.

Failure and recovery for active standby pair grid members

If both nodes of an active standby pair grid member fail, then the grid member fails. Oracle Clusterware evicts the failed grid member from the grid automatically. However, when a cache grid is configured, any further automatic recovery after a dual failure, whether temporary or permanent, is not possible. In this case, you can only recover manually. For details, see "Manual recovery of both nodes of an active standby pair grid member".

Making schema changes to active standby pairs in a grid

You can add, drop, or change a cache group while the active master database is attached to the grid.

Use the ttCWAdmin -beginAlterSchema command to make these schema changes. This command stops the replication agents on both the active and standby master nodes, but allows the active master database to remain attached to the grid. The ttCWAdmin -endAlterSchema command initiates a duplicate to propagate certain changes to the standby master database (and any subscribers), registers the altered replication scheme, restarts both replication agents, and reinstates Oracle Clusteware control.

Note:
The ttCWadmin -endAlterSchema command initiates a duplicate for this case since cache groups are included in the replication schema, but the DDL statements for cache groups are not replicated. For full details, see "Changing the schema".

To add or drop a replicated table into the active standby pair, see "Making DDL changes in an active standby pair".

Add a cache group

Perform these steps on the active database of each active standby pair grid member.

Note:
These steps are the same whether the active standby pair is or is not included in a cache grid.

1. Enable the addition of the cache group to the active standby pair by temporarily suspending Oracle Clusterware management and stopping the replication agents with the ttCWAdmin -beginAlterSchema command.

ttCWAdmin -beginAlterSchema -dsn advancedDSN

2. Create the cache group.

3. If the cache group is a read-only cache group, alter the active standby pair to include the cache group.

ALTER ACTIVE STANDBY PAIR INCLUDE CACHE GROUP samplecachegroup;

4. Complete your changes by executing the ttCWAdmin -endAlterSchema command. Since you added a cache group object, a duplicate occurs to propagate these schema changes to the standby master database.

ttCWAdmin -endAlterSchema -dsn advancedDSN

You can load the cache group at any time after you create the cache group.

Drop a cache group

Perform these steps to drop a cache group.

Note:
These steps are the same whether the active standby pair is or is not included in a cache grid.

1. Unload the cache group. When using a cache grid, you must unload the cache group in all members of the cache grid.

CALL ttOptSetFlag('GlobalProcessing', 1);
UNLOAD CACHE GROUP samplecachegroup;

2. On the active database of an active standby pair, enable dropping the cache group.

ttCWAdmin -beginAlterSchema -dsn advancedDSN

3. If the cache group is a read-only cache group, alter the active standby pair to exclude the cache group.

ALTER ACTIVE STANDBY PAIR EXCLUDE CACHE GROUP samplecachegroup;

4. If the cache group is a read-only cache group, set the autorefresh state to PAUSED.

ALTER CACHE GROUP samplecachegroup SET AUTOREFRESH STATE PAUSED;

5. Drop the cache group.

DROP CACHE GROUP samplecachegroup;

6. If the cache group was a read-only cache group, run the TimesTen_install_dir/oraclescripts/cacheCleanUp.sql SQL*Plus script as the cache administration user on the Oracle database to drop the Oracle database objects used to implement autorefresh operations.

7. Complete your changes by executing the ttCWAdmin -endAlterSchema command. Since you dropped a cache group object, a duplicate occurs to propagate these schema changes to the standby master database.

ttCWAdmin -endAlterSchema -dsn advancedDSN

8. Repeat steps 2 through 7 on the active database of each active standby pair grid member.

Change an existing cache group

To change an existing cache group, first drop the existing cache group as described in "Drop a cache group". Then add the cache group with the desired changes as described in "Add a cache group".

Recovering from failures

Oracle Clusterware can recover automatically from many kinds of failures. The following sections describe several failure scenarios and how Oracle Clusterware manages the failures.

- How TimesTen performs recovery when Oracle Clusterware is configured

- When an active database or its host fails

- When a standby database or its host fails

- When read-only subscribers or their hosts fail

- When failures occur on both master nodes

- When more than two master hosts fail

- Perform a forced switchover after failure of the active database or host

How TimesTen performs recovery when Oracle Clusterware is configured

The TimesTen database monitor (ttCRSmaster process) performs recovery. It attempts to connect to the failed database without using the forceconnect option. If the connection fails with error 994 (Data store connection terminated), the database monitor tries to connect 10 times. If the connection fails with error 707 (Attempt to connect to a data store that has been manually unloaded from RAM), the database monitor changes the RAM policy and tries to connect again. If the database monitor cannot connect, it returns connection failure.

If the database monitor can connect to the database, then it performs these tasks:

- It queries the CHECKSUM column in the TTREP.REPLICATIONS replication table.

- If the value in the CHECKSUM column matches the checksum stored in the Oracle Cluster Registry, then the database monitor verifies the role of the database. If the role is 'ACTIVE', then recovery is complete.
If the role is not 'ACTIVE', then the database monitor queries the replication Commit Ticket Number (CTN) in the local database and the CTN in the active database to find out whether there are transactions that have not been replicated. If all transactions have been replicated, then recovery is complete.

- If the checksum does not match or if some transactions have not been replicated, then the database monitor performs a duplicate operation from the remote database to re-create the local database.

If the database monitor fails to connect with the database because of error 8110 or 8111 (master catchup required or in progress), then it uses the forceconnect=1 option to connect and starts master catchup. Recovery is complete when master catchup has been completed. If master catchup fails with error 8112 (Operation not permitted), then the database monitor performs a duplicate operation from the remote database. For more information about master catchup, see "Automatic catch-up of a failed master database".

If the connection fails because of other errors, then the database monitor tries to perform a duplicate operation from the remote database.

The duplicate operation verifies that:

- The remote database is available.

- The replication agent is running.

- The remote database has the correct role. The role must be 'ACTIVE' when the duplicate operation is attempted for creation of a standby database. The role must be 'STANDBY' or 'ACTIVE' when the duplicate operation is attempted for creation of a read-only subscriber.

When the conditions for the duplicate operation are satisfied, the existing failed database is destroyed and the duplicate operation starts.

When an active database or its host fails

If there is a failure on the node where the active database resides, Oracle Clusterware automatically changes the state of the standby database to 'ACTIVE'. If application failover is configured, then the application begins updating the new active database.

Figure 8-2 shows that the state of the standby database has changed to 'ACTIVE' and that the application is updating the new active database.

Figure 8-2 Standby database becomes active

Oracle Clusterware tries to restart the database or host where the failure occurred. If it is successful, then that database becomes the standby database.

Figure 8-3 shows a cluster where the former active node becomes the standby node.

Figure 8-3 Standby database starts on former active host

If the failure of the former active node is permanent and advanced availability is configured, Oracle Clusterware starts a standby database on one of the extra nodes.

Figure 8-4 shows a cluster in which the standby database is started on one of the extra nodes.

Figure 8-4 Standby database starts on extra host

If you do not want to wait for these automatic actions to occur, see "Perform a forced switchover after failure of the active database or host".

When a standby database or its host fails

If there is a failure on the standby node, Oracle Clusterware first tries to restart the database or host. If it cannot restart the standby database on the same host and advanced availability is configured, Oracle Clusterware starts the standby database on an extra node.

Figure 8-5 shows a cluster in which the standby database is started on one of the extra nodes.

Figure 8-5 Standby database on new host

When read-only subscribers or their hosts fail

If there is a failure on a subscriber node, Oracle Clusterware first tries to restart the database or host. If it cannot restart the database on the same host and advanced availability is configured, Oracle Clusterware starts the subscriber database on an extra node.

When failures occur on both master nodes

This section includes these topics:

- Automatic recovery when not attached to a grid

- Manual recovery of both nodes of an active standby pair grid member

- Manual recovery for advanced availability

- Manual recovery for basic availability

- Manual recovery to the same master nodes when databases are corrupt

- Manual recovery when RETURN TWOSAFE is configured

Automatic recovery when not attached to a grid

Oracle Clusterware can achieve automatic recovery from temporary failure on both master nodes after the nodes come back up if:

- RETURN TWOSAFE is not specified for the active standby pair.

- AutoRecover is set to y.

- RepBackupDir specifies a directory on shared storage.

- RepBackupPeriod is set to a value greater than 0.

Oracle Clusterware can achieve automatic recovery from permanent failure on both master nodes if:

- Advanced availability is configured (virtual IP addresses and at least four hosts).

- The active standby pair does not replicate cache groups.

- A cache grid is not configured.

- RETURN TWOSAFE is not specified for the active standby pair.

- AutoRecover is set to y.

- RepBackupDir specifies a directory on shared storage.

- RepBackupPeriod is set to a value greater than 0.

See "Recovering from permanent failure of both master nodes" for examples of cluster.oracle.ini files.

Manual recovery of both nodes of an active standby pair grid member

If both nodes of an active standby pair grid member fail, then the grid member fails. Oracle Clusterware evicts the failed grid member from the grid automatically. After the failed grid member is removed from the grid, you can continue to recover manually. However, when a cache grid is configured, any further automatic recovery after a dual failure, whether temporary or permanent, is not possible.

If the active standby pair grid member is in an asynchronous replication scheme, the grid member is recovered automatically and reattached to the grid. If the active standby pair grid member is in a replication scheme with RETURN TWOSAFE configured, perform these steps to recover the grid member and reattach it to the grid:

1. Stop the replication agent and the cache agent and disconnect the application from both databases. This step detaches the grid member from the grid.

ttCWAdmin -stop advancedGridDSN

2. Drop the active standby pair.

ttCWAdmin -drop advancedGridDSN

3. Create the active standby pair replication scheme.

ttCWAdmin -create advancedGridDSN

4. Start the active standby pair replication scheme. This step attaches the grid member to the grid.

ttCWAdmin -start advancedGridDSN

Manual recovery for advanced availability

This section assumes that the failed master nodes are recovered to new hosts on which TimesTen and Oracle Clusterware are installed. These steps use the manrecoveryDSN database and cluster.oracle.ini file for examples.

To perform manual recovery in an advanced availability configuration, perform these tasks:

1. Ensure that the TimesTen cluster agent is running on the local host.

ttCWAdmin -init -hosts localhost

2. Restore the backup database. Ensure that there is not already a database on the host with the same DSN as the database you want to restore.

ttCWAdmin -restore -dsn manrecoveryDSN

3. If there are cache groups in the database, drop and re-create the cache groups.

4. If the new hosts are not already specified by MasterHosts and SubscriberHosts in the cluster.oracle.ini file, then modify the file to include the new hosts.
These steps use manrecoveryDSN. This step is not necessary for manrecoveryDSN because extra hosts are already specified in the cluster.oracle.ini file.

5. Re-create the active standby pair replication scheme.

ttCWAdmin -create -dsn manrecoveryDSN

6. Start the active standby pair replication scheme.

ttCWAdmin -start -dsn manrecoveryDSN

Manual recovery for basic availability

This section assumes that the failed master nodes are recovered to new hosts on which TimesTen and Oracle Clusterware are installed. These steps use the basicDSN database and cluster.oracle.ini file for examples.

To perform manual recovery in a basic availability configuration, perform these steps:

1. Acquire new hosts for the databases in the active standby pair.

2. Ensure that the TimesTen cluster agent is running on the local host.

ttCWAdmin -init -hosts localhost

3. Restore the backup database. Ensure that there is not already a database on the host with the same DSN as the database you want to restore.

ttCWAdmin -restore -dsn basicDSN

4. If there are cache groups in the database, drop and re-create the cache groups.

5. Update the MasterHosts and SubscriberHosts entries in the cluster.oracle.ini file. This example uses the basicDSN database. The MasterHosts entry changes from host1 to host10. The SubscriberHosts entry changes from host2 to host20.

[basicDSN]
MasterHosts=host10,host20

6. Re-create the active standby pair replication scheme.

ttCWAdmin -create -dsn basicDSN

7. Start the active standby pair replication scheme.

ttCWAdmin -start -dsn basicDSN

Manual recovery to the same master nodes when databases are corrupt

Failures can occur on both master nodes so that the databases are corrupt. If you want to recover to the same master nodes, perform the following steps:

1. Ensure that the replication agent and the cache agent are stopped and that applications are disconnected from both databases. This example uses the basicDSN database.

ttCWAdmin -stop -dsn basicDSN

2. On the node where you want the new active database to reside, destroy the databases by using the ttDestroy utility.

ttDestroy basicDSN

3. Restore the backup database.

ttCWAdmin -restore -dsn basicDSN

4. If there are cache groups in the database, drop and re-create the cache groups.

5. Re-create the active standby pair replication scheme.

ttCWAdmin -create -dsn basicDSN

6. Start the active standby pair replication scheme.

ttCWAdmin -start -dsn basicDSN

Manual recovery when RETURN TWOSAFE is configured

You can configure an active standby pair to have a return service of RETURN TWOSAFE by using the ReturnServiceAttribute Clusterware attribute in the cluster.oracle.ini file. When RETURN TWOSAFE is configured, the database logs may be available on one or both nodes after both nodes fail.

This cluster.oracle.ini example includes backup configuration in case the database logs are not available:

[basicTwosafeDSN]
MasterHosts=host1,host2
ReturnServiceAttribute=RETURN TWOSAFE
RepBackupDir=/shared_drive/dsbackup
RepBackupPeriod=3600

Perform these recovery tasks:

1. Ensure that the replication agent and the cache agent are stopped and that applications are disconnected from both databases.

ttCWAdmin -stop -dsn basicTwosafeDSN

2. Drop the active standby pair.

ttCWAdmin -drop -dsn basicTwosafeDSN

3. Decide whether the former active or standby database is more up to date and re-create the active standby pair using the chosen database. The command prompts you to choose the host on which the active database resides.

ttCWAdmin -create -dsn basicTwosafeDSN

If neither database is usable, restore the database from backups.

ttCWAdmin -restore -dsn basicTwosafeDSN

4. Start the active standby pair replication scheme.

ttCWAdmin -start -dsn basicTwosafeDSN

When more than two master hosts fail

Approach a failure of more than two master hosts as a more extreme case of dual host failure. Use these guidelines:

- Address the root cause of the failure if it is something like a power outage or network failure.

- Identify or obtain at least two healthy hosts for the active and standby databases.

- Update the MasterHosts and SubscriberHosts entries in the cluster.oracle.ini file.

- See "Manual recovery for advanced availability" and "Manual recovery for basic availability" for guidelines on subsequent actions to take.

Perform a forced switchover after failure of the active database or host

If you want to force a switchover to the standby database without waiting for automatic recovery to be performed by TimesTen and Oracle Clusterware, you can write an application that uses Oracle Clusterware commands.

Perform the following:

1. Use the crsctl stop resource command to stop the ttCRSmaster resource on the active database. This causes the role of the standby database to change to active.

2. Use the crsctl start resource command to restart the ttCRSmaster resource on the former active database. This causes the database to recover and become the standby database.

The following example demonstrates a forced switchover from the active database on host1 to the standby database on host2.

1. Find all TimesTen resources using the crsctl status resource command.

% crsctl status resource | grep TT
NAME=TT_Activeservice_tt1122_ttadmin_REP1
NAME=TT_Agent_tt1122_ttadmin_HOST1
NAME=TT_Agent_tt1122_ttadmin_HOST2
NAME=TT_App_tt1122_ttadmin_REP1_updateemp
NAME=TT_Daemon_tt1122_ttadmin_HOST1
NAME=TT_Daemon_tt1122_ttadmin_HOST2
NAME=TT_Master_tt1122_ttadmin_REP1_0
NAME=TT_Master_tt1122_ttadmin_REP1_1
NAME=TT_Subservice_tt1122_ttadmin_REP1

2. Find the host where the active database resides by retrieving the status of the ttCRSActiveService resource.

% crsctl status resource TT_Activeservice_tt1122_ttadmin_REP1
NAME=TT_Activeservice_tt1122_ttadmin_REP1
TYPE=application
TARGET=ONLINE
STATE=ONLINE on host1

3. There are two ttCRSmaster resources listed in the initial status report. Discover which ttCRSmaster resource is on the same host as the active database.

% crsctl status resource TT_Master_tt1122_ttadmin_REP1_0
NAME=TT_Master_tt1122_ttadmin_REP1_0
TYPE=application
TARGET=ONLINE
STATE=ONLINE on host1

% crsctl status resource TT_Master_tt1122_ttadmin_REP1_1
NAME=TT_Master_tt1122_ttadmin_REP1_1
TYPE=application
TARGET=ONLINE
STATE=ONLINE on host2

4. Stop the ttCRSmaster resource on the host where the active database resides.

% crsctl stop resource TT_Master_tt1122_ttadmin_REP1_0
CRS-2673: Attempting to stop 'TT_Master_tt1122_ttadmin_REP1_0'
on 'host1'
CRS-2677: Stop of 'TT_Master_tt1122_ttadmin_REP1_0' on
'host1' succeeded

5. Restart the ttCRSmaster resource on the former active database.

% crsctl start resource TT_Master_tt1122_ttadmin_REP1_0
CRS-2672: Attempting to start 'TT_Master_tt1122_ttadmin_REP1_0'
on 'host1'
CRS-2676: Start of 'TT_Master_tt1122_ttadmin_REP1_0' on
'host1' succeeded

6. Confirm that the forced switchover succeeds by checking where the ttCRSActiveService and ttCRSsubservice resources are located.

% crsctl status resource TT_Activeservice_tt1122_ttadmin_REP1
NAME=TT_Activeservice_tt1122_ttadmin_REP1
TYPE=application
TARGET=ONLINE
STATE=ONLINE on host2

% crsctl status resource TT_Subservice_tt1122_ttadmin_REP1
NAME=TT_Subservice_tt1122_ttadmin_REP1
TYPE=application
TARGET=ONLINE
STATE=ONLINE on host1

See Oracle Clusterware Administration and Deployment Guide for more information about the crsctl start resource and crsctl stop resource commands.

Clusterware management

This section includes the following topics:

- Performing a rolling upgrade of Oracle Clusterware software

- Upgrading TimesTen

- Managing hosts in the cluster

- Managing active standby pairs in a cluster

- Managing read-only subscribers in the active standby pair

- Changing the schema

- Reversing the roles of the master databases

- Moving a database to a different host

- Performing host or network maintenance

- Performing maintenance on the entire cluster

- Changing user names or passwords when using Oracle Clusterware

Performing a rolling upgrade of Oracle Clusterware software

See Oracle Clusterware Administration and Deployment Guide.

Upgrading TimesTen

See "Performing an online TimesTen upgrade when using Oracle Clusterware" in Oracle TimesTen In-Memory Database Installation Guide.

Managing hosts in the cluster

The following sections describe how to add or remove hosts when using a cluster:

- Adding a host to the cluster

- Removing a host from the cluster

Adding a host to the cluster

Adding a host requires that the cluster be configured for advanced availability. The examples in this section use the advancedSubscriberDSN.

To add two spare master hosts to a cluster, enter a command similar to the following:

ttCWAdmin -addMasterHosts -hosts "host8,host9" -dsn advancedSubscriberDSN

To add a spare subscriber host to a cluster, enter a command similar to the following:

ttCWAdmin -addSubscriberHosts -hosts "subhost1" -dsn advancedSubscriberDSN

Removing a host from the cluster

Removing a host from the cluster requires that the cluster be configured for advanced availability. MasterHosts must list more than two hosts if one of the master hosts is to be removed. SubscriberHosts must list at least one more host than the number of subscriber databases if one of the subscriber hosts is to be removed.

The examples in this section use the advancedSubscriberDSN.

To remove two spare master host from the cluster, enter a command similar to the following:

ttCWAdmin -delMasterHosts "host8,host9" -dsn advancedSubscriberDSN

To remove a spare subscriber hosts from the cluster, enter a command similar to the following:

ttCWAdmin -delSubscriberHosts "subhost1" -dsn advancedSubscriberDSN

Managing active standby pairs in a cluster

The following sections describe how to add or remove an active standby pair to a cluster:

- Adding an active standby pair to a cluster

- Removing an active standby pair from a cluster

Adding an active standby pair to a cluster

To add an active standby pair (with or without subscribers) to a cluster that is already managing an active standby pair, perform these tasks:

1. Create and populate a database on the host where you intend the active database to reside initially. See "Create and populate a TimesTen database on one host".

2. Modify the cluster.oracle.ini file. This example adds advSub2DSN to the cluster.oracle.ini file that already contains the configuration for advancedSubscriberDSN. The new active standby pair is on different hosts from the original active standby pair.

[advancedSubscriberDSN]
MasterHosts=host1,host2,host3
SubscriberHosts=host4, host5
MasterVIP=192.168.1.1, 192.168.1.2
SubscriberVIP=192.168.1.3
VIPInterface=eth0
VIPNetMask=255.255.255.0

[advSub2DSN]
MasterHosts=host6,host7,host8
SubscriberHosts=host9, host10
MasterVIP=192.168.1.4, 192.168.1.5
SubscriberVIP=192.168.1.6
VIPInterface=eth0
VIPNetMask=255.255.255.0

3. Create new virtual IP addresses as the root user.

ttCWAdmin -createVIPs -dsn advSub2DSN

4. Create the new active standby pair replication scheme.

ttCWAdmin -create -dsn advSub2DSN

5. Start the new active standby pair replication scheme.

ttCWAdmin -start -dsn advSub2DSN

Removing an active standby pair from a cluster

To remove an active standby pair (with or without subscribers) from a cluster, perform these tasks:

1. Stop the replication agents on all databases in the active standby pair. This example uses advSub2DSN, which was added in "Adding an active standby pair to a cluster".

ttCWAdmin -stop -dsn advSub2DSN

2. Drop the active standby replication scheme.

ttCWAdmin -drop -dsn advSub2DSN

3. Drop the virtual IP addresses for the active standby pair.

ttCWAdmin -dropVIPs -dsn advSub2DSN

4. Modify the cluster.oracle.ini file (optional). Remove the entries for advSub2DSN.

5. If you want to destroy the databases, log onto each host that was included in the configuration for this active standby pair and use the ttDestroy utility.

ttDestroy advSub2DSN

For more information about ttDestroy, see "ttDestroy" in Oracle TimesTen In-Memory Database Reference.

Managing read-only subscribers in the active standby pair

The following sections describe how to manage read-only subscribers in the active standby pair that is managed by Oracle Clusterware:

- Adding a read-only subscriber managed by Oracle Clusterware

- Removing a read-only subscriber managed by Oracle Clusterware

- Adding or dropping a read-only subscriber not managed by Oracle Clusterware

- Rebuilding a read-only subscriber not managed by Oracle Clusterware

Adding a read-only subscriber managed by Oracle Clusterware

To add a read-only subscriber that is to be managed by Oracle Clusterware to an active standby pair replication scheme, perform these steps:

1. Stop the replication agents on all databases. This example uses the advancedSubscriberDSN, which already has a subscriber and is configured for advanced availability.

ttCWAdmin -stop -dsn advancedSubscriberDSN

2. Drop the active standby pair.

ttCWAdmin -drop -dsn advancedSubscriberDSN

3. Modify the cluster.oracle.ini file.

- Add the subscriber to the SubscriberHosts attribute.

- If the cluster is configured for advanced availability, add a virtual IP address to the SubscriberVIP attribute.

See "Configuring advanced availability" for an example using these attributes.

4. Create the active standby pair replication scheme.

ttCWAdmin -create -dsn advancedSubscriberDSN

5. Start the active standby pair replication scheme.

ttCWAdmin -start -dsn advancedSubscriberDSN

Removing a read-only subscriber managed by Oracle Clusterware

To remove a read-only subscriber that is managed by Oracle Clusterware from an active standby pair, perform these steps:

1. Stop the replication agents on all databases. This example uses the advancedSubscriberDSN, which has a subscriber and is configured for advanced availability.

ttCWAdmin -stop -dsn advancedSubscriberDSN

2. Drop the active standby pair.

ttCWAdmin -drop -dsn advancedSubscriberDSN

3. Modify the cluster.oracle.ini file.

- Remove the subscriber from the SubscriberHosts attribute or remove the attribute altogether if there are no subscribers left in the active standby pair.

- Remove a virtual IP from the SubscriberVIP attribute or remove the attribute altogether if there are no subscribers left in the active standby pair.

4. Create the active standby pair replication scheme.

ttCWAdmin -create -dsn advancedSubscriberDSN

5. Start the active standby pair replication scheme.

ttCWAdmin -start -dsn advancedSubscriberDSN

Adding or dropping a read-only subscriber not managed by Oracle Clusterware

You can add or drop a read-only subscriber that is not managed by Oracle Clusterware to or from an existing active standby pair replication scheme that is managed by Oracle Clusterware. Using the ttCWAdmin -beginAlterSchema command enables you to add a subscriber without dropping and re-creating the replication scheme. Oracle Clusterware does not manage the subscriber, because it is not part of the configuration that was set up for Oracle Clusterware management.

Perform these steps:

1. Execute the ttCWAdmin -beginAlterSchema command to stop the replication agent on the active and standby databases.

2. Using ttIsql to connect to the active database, you can add or drop the subscriber to or from the replication scheme by using an ALTER ACTIVE STANDBY PAIR statement. For example, to add a subscriber:

ALTER ACTIVE STANDBY PAIR ADD SUBSCRIBER ROsubDSN ON host6;

To drop a subscriber:

ALTER ACTIVE STANDBY PAIR DROP SUBSCRIBER ROsubDSN ON host6;

3. Execute the ttCWAdmin -endAlterSchema command that registers the altered replication scheme and starts replication. If you are adding a subscriber, this also initiates a duplicate to the standby master database.

4. Execute the ttIsql repschemes command to verify that the read-only subscriber has been added to or dropped from the replication scheme.

5. Use the ttRepStateGet built-in procedure to verify that the state of the standby database is STANDBY.

6. If you added a subscriber, then execute ttRepAdmin -duplicate on the subscriber host to duplicate the standby database to the read-only subscriber. See "Duplicating a database".

7. If you added a subscriber, start the replication agent on the subscriber host.

If you added a subscriber, ensure that the read-only subscriber is included if the cluster is dropped and re-created by adding the RemoteSubscriberHosts Clusterware attribute for the read-only subscriber in the cluster.oracle.ini file as described in Step 1 in "Configure a read-only subscriber that is not managed by Oracle Clusterware". Alternatively, if you dropped a subscriber, remove the RemoteSubscriberHosts Clusterware attribute for the dropped subscriber in the cluster.oracle.ini file (if it is configured).

Rebuilding a read-only subscriber not managed by Oracle Clusterware

Perform the following tasks to destroy and rebuild a read-only subscriber that is not managed by Oracle Clusterware:

1. Stop the replication agent on the subscriber host.

2. Use the ttDestroy utility to destroy the subscriber database.

3. On the subscriber host, use ttRepAdmin -duplicate to duplicate the standby database to the read-only subscriber. See "Duplicating a database".

Changing the schema

When using Oracle Clusterware to manage an active standby pair, you can modify the schema by executing DDL statements as in a normal replication environment, except that Oracle Clusterware must start and stop all replication agents, when it is necessary to do so.

Thus, when you change the schema, note the following:

- For those DDL statements on objects that are automatically replicated, you do not need to stop the replication agents. In this case, no further action is required, since these DDL statements are automatically propagated and applied to the standby master and any subscribers. The DDLReplicationLevel connection attribute controls what DDL statements are replicated.

- For those objects that are a part of the replication scheme, but any DDL statements executed on these objects are not replicated (these objects are listed in "Making other changes to an active standby pair"), run the Oracle Clusterware ttCWAdmin -beginAlterSchema command on the active master, which stops the replication agents on each node in the replication scheme. Then, execute the DDL statement on the active master in the replication scheme. Finally, run the Oracle Clusterware ttCWAdmin -endAlterSchema command on the active master to restart all replication agents.
Because these objects are a part of the replication scheme, but the DDL statements are not replicated, a duplicate occurs after the ttCWAdmin -endAlterSchema command to propagate these schema changes to the standby master and any subscribers. This is the only scenario when a duplicate is used to propagate the schema changes.

Follow the instructions described in "Facilitating schema change for Oracle Clusterware".

- For those DDL statements on objects that are not automatically replicated and are not part of the replication scheme, run the Oracle Clusterware ttCWAdmin -beginAlterSchema command on the active master, which stops the replication agents on all nodes. Then, you can synchronize all nodes by manually executing these DDL statements as indicated in "Making DDL changes in an active standby pair." Finally, run the Oracle Clusterware ttCWAdmin -endAlterSchema command on the active master to restart all replication agents.
Follow the instructions described in "Facilitating schema change for Oracle Clusterware".

Note:
The "Making DDL changes in an active standby pair" and "Making other changes to an active standby pair" sections describe which DDL statements are and are not automatically replicated for an active standby pair. These sections also describe what objects are a part of the replication scheme.

Facilitating schema change for Oracle Clusterware

Use the ttCWAdmin -beginAlterSchema and -endAlterSchema commands to facilitate the schema changes on the active and standby master databases that requires the replication agents are stopped.

- The ttCWAdmin -beginAlterSchema command prepares for schema changes by stopping replication agents on both the active and standby master nodes in preparation for any schema changes.

- After you complete all schema changes, run the ttCWAdmin -endAlterSchema command. For those objects that are a part of the replication scheme, but any DDL statements executed on these objects are not automatically replicated, a duplicate occurs after the ttCWAdmin -endAlterSchema command to propagate only these schema changes to the standby and any subscribers. This command registers the altered replication scheme, restarts the replication agents on the active and standby master nodes, and reinstates Oracle Clusteware control.

Perform the following tasks when altering the schema of the active standby pair when using Oracle Clusterware:

1. Enable the changes to the schema of the active standby pair by stopping the replication agents on both the active and standby masters.

ttCWAdmin -beginAlterSchema -dsn advancedDSN

2. Make any desired schema changes.
If you create, alter, or drop any objects where the DDL for these objects are not replicated, you should also manually create, alter, or drop the same objects on the standby master and subscribers while the replication agents are inactive to ensure that the same objects exist on all databases in the replication scheme. For example, if you create a materialized view on the active database, create the materialized view on the databases on the standby master and subscriber nodes at this time.

3. If the object is not automatically replicated but is a part of the replication scheme, (such as a sequence) and you want to include it in the active standby pair replication scheme, alter the active standby pair.

ALTER ACTIVE STANDBY PAIR INCLUDE samplesequence;

4. If the object is a cache group, see the instructions for creating, altering, or dropping a cache group in "Making schema changes to active standby pairs in a grid".

5. Run the ttCWAdmin -endAlterSchema command to restart the replication agents on the active and standby master nodes. If you modified objects that are a part of the replication scheme, but any DDL statements executed on these objects are not automatically replicated, a duplicate occurs after the ttCWAdmin -endAlterSchema command to propagate only these schema changes to the standby and any subscribers.

ttCWAdmin -endAlterSchema -dsn advancedDSN

Managing subscribers and database attributes

To add or drop a subscriber database or alter database attributes, perform the following tasks:

1. Stop the replication agents on the databases in the active standby pair. These commands use the advancedCacheDSN as an example.

ttCWAdmin -stop -dsn advancedCacheDSN

2. Drop the active standby pair.

ttCWAdmin -drop  -dsn advancedCacheDSN

3. Modify the schema as desired.

4. Re-create the active standby pair replication scheme.

ttCWAdmin -create -dsn advancedCacheDSN

5. Start the active standby pair replication scheme.

ttCWAdmin -start -dsn advancedCacheDSN

Reversing the roles of the master databases

After a failover, the active and standby databases are on different hosts than they were before the failover. You can use the -switch option of the ttCWAdmin utility to restore the original configuration. Optionally, you can also use the -timeout option with the -switch option to set a timeout for the number of seconds to wait for the active and standby database switch to complete.

For example:

ttCWAdmin -switch -dsn basicDSN

Ensure that there are no open transactions before using the -switch option. If there are open transactions, the command fails.

Note:
For more details on the -switch and -timeout options, see "ttCWAdmin" in the Oracle TimesTen In-Memory Database Reference.

Figure 8-6 shows the hosts for an active standby pair. The active database resides on host A, and the standby database resides on host B.

Figure 8-6 Hosts for an active standby pair

The ttCWAdmin -switch command performs these tasks:

- Deactivates the TimesTen cluster agent (ttCRSAgent) on host A (the active node).

- Disables the database monitor (ttCRSmaster) on host A.

- Calls the ttRepSubscriberWait, ttRepStop and ttRepDeactivate built-in procedures on host A.

- Stops the active service (ttCRSActiveService) on host A and reports a failure event to the Oracle Clusterware CRSD process.

- Enables monitoring on host A and moves the active service to host B.

- Starts the replication agent on host A, stops the standby service (ttCRSsubservice) on host B and reports a failure event to the Oracle Clusterware CRSD process on host B.

- Starts the standby service (ttCRSsubservice) on host A.

Moving a database to a different host

When a cluster is configured for advanced availability, you can use the -relocate option of the ttCWAdmin utility to move a database from the local host to the next available spare host specified in the MasterHosts attribute in the cluster.oracle.ini file. If the database on the local host has the active role, the -relocate option first reverses the roles. Thus, the newly migrated active database becomes the standby and the standby becomes the active.

The -relocate option is useful for relocating a database if you decide to take the host offline. Ensure that there are no open transactions before you use the command.

If the -relocate option requires a role switch, then you can optionally use the -timeout option with the -relocate option to set a timeout for the number of seconds to wait for the role switch.

For example:

ttCWAdmin -relocate -dsn advancedDSN

Note:
For more details on the -relocate and -timeout options, see "ttCWAdmin" in the Oracle TimesTen In-Memory Database Reference.

Performing host or network maintenance

If you decide to upgrade the operating system or hardware for a host or perform network maintenance, shut down Oracle Clusterware and disable automatic startup. Execute these Oracle Clusterware commands as root or OS administrator:

# crsctl stop crs

# crsctl disable crs

Shut down TimesTen. See "Shutting down a TimesTen application" in Oracle TimesTen In-Memory Database Operations Guide.

Perform the host maintenance. Then enable automatic startup and start Oracle Clusterware:

# crsctl enable crs

# crsctl start crs

See Oracle Clusterware Administration and Deployment Guide for more information about these commands.

Performing maintenance on the entire cluster

When all of the hosts in the cluster need to be brought down, stop Oracle Clusterware on each host individually. Execute these Oracle Clusterware commands as root or OS administrator:

# crsctl stop crs

# crsctl disable crs

Shut down TimesTen. See "Shutting down a TimesTen application" in Oracle TimesTen In-Memory Database Operations Guide.

Perform the maintenance. Then enable automatic startup and start Oracle Clusterware:

# crsctl enable crs

# crsctl start crs

See Oracle Clusterware Administration and Deployment Guide for more information about these commands.

Changing user names or passwords when using Oracle Clusterware

When you create the active standby pair replication scheme with the ttCWAdmin -create command, Oracle Clusterware prompts for the required user names and passwords in order to manage the TimesTen environment. Oracle Clusterware stores these user names and passwords. After modifying any user name or password, you must execute the ttCWAdmin -reauthenticate command to enable Oracle Clusterware to store these new user names and passwords.

1. Ensure that the DDLReplicationLevel connection attribute is set to 3. This value replicates changes to the user names or passwords on the active master to the standby master.

2. Modify any of the user names or passwords in the same manner (and with the same restrictions) as described in "Changing user names or passwords used by replication".

3. Ensure that all password changes are replicated to the standby master by calling the ttRepSubscriberWait built-in procedure (or the ttRepAdmin -wait command) on the active master database using the DSN and host of the standby master database. For example, to ensure that all transactions are replicated to the master2 standby master on the host2 host:

Command> CALL ttRepSubscriberWait(NULL, NULL, 'master2', 'host2', -1);

4. Store the new passwords in Oracle Clusterware by executing the ttCWAdmin -reauthenticate command.

ttCWAdmin -reauthenticate -dsn myDSN

This command prompts for the same information as requested for the ttCWAdmin -create command, which is discussed in "Create an active standby pair replication scheme".

Managing the TimesTen database RAM policy

By default, the TimesTen database RAM policy is set to Always when Oracle Clusterware manages the TimesTen database. However, if you stop Oracle Clusterware management, the TimesTen database RAM policy is set to In Use.

If you no longer use Oracle Clusterware to manage TimesTen, you should set the TimesTen RAM policy to what is appropriate for your envioronment. Typically, the recommended setting is Manual.

For more information on the TimesTen database RAM policy, see "Specifying a RAM policy" in the Oracle TimesTen In-Memory Database Operations Guide.

Monitoring cluster status

The following sections describe how to retrieve the status of the cluster:

- Obtaining cluster status

- Message log files

Obtaining cluster status

The -status option of the ttCWAdmin utility reports information about all of the active standby pairs in an instance that are managed by the same instance administrator. If you specify the DSN, the utility reports information for the active standby pair with that DSN.

Example 8-1 Status after creating an active standby pair

After you have created an active standby pair replication scheme but have not yet started replication, ttCWAdmin -status returns information such as this. Note that the grid states are displayed before replication is started, regardless of whether there is a cache grid.

$ ttCWAdmin -status
TimesTen Cluster status report as of Thu Nov 11 13:54:35 2010

====================================================================
TimesTen daemon monitors:
Host:HOST1 Status: online
Host:HOST2 Status: online

====================================================================
====================================================================
TimesTen Cluster agents
Host:HOST1 Status: online
Host:HOST2 Status: online

====================================================================

Status of Cluster related to DSN MYDSN:
====================================================================
1. Status of Cluster monitoring components:
Monitor Process for Active datastore:NOT RUNNING
Monitor Process for Standby datastore:NOT RUNNING
Monitor Process for Master Datastore 1 on Host host1: NOT RUNNING
Monitor Process for Master Datastore 2 on Host host2: NOT RUNNING

2.Status of  Datastores comprising the cluster
Master Datastore 1:
Host:host1
Status:AVAILABLE
State:ACTIVE
Grid:NO GRID
Master Datastore 2:
Host:host2
Status:UNAVAILABLE
State:UNKNOWN
Grid:UNKNOWN
====================================================================
The cluster containing the replicated DSN is offline

Example 8-2 Status when the active database is running

After you have started the replication scheme and the active database is running but the standby database is not yet running, ttCWAdmin -status returns information like this when a cache grid is not configured.

$ ttcwadmin -status
TimesTen Cluster status report as of Thu Nov 11 13:58:25 2010

====================================================================
TimesTen daemon monitors:
Host:HOST1 Status: online
Host:HOST2 Status: online

====================================================================
====================================================================
TimesTen Cluster agents
Host:HOST1 Status: online
Host:HOST2 Status: online

====================================================================

Status of Cluster related to DSN MYDSN:
====================================================================
1. Status of Cluster monitoring components:
Monitor Process for Active datastore:RUNNING on Host host1
Monitor Process for Standby datastore:RUNNING on Host host1
Monitor Process for Master Datastore 1 on Host host1: RUNNING
Monitor Process for Master Datastore 2 on Host host2: RUNNING

2.Status of  Datastores comprising the cluster
Master Datastore 1:
Host:host1
Status:AVAILABLE
State:ACTIVE
Grid:NO GRID
Master Datastore 2:
Host:host2
Status:AVAILABLE
State:IDLE
Grid:NO GRID
====================================================================
The cluster containing the replicated DSN is online

If a cache grid is configured, then the last section appears as follows:

2.Status of  Datastores comprising the cluster
Master Datastore 1:
Host:host1
Status:AVAILABLE
State:ACTIVE
Grid:AVAILABLE
Master Datastore 2:
Host:host2
Status:AVAILABLE
State:IDLE
Grid:NO GRID

Example 8-3 Status when the active and the standby databases are running

After you have started the replication scheme and the active database and the standby database are both running, ttCWAdmin -status returns information like this when a cache grid is not configured.

$ ttcwadmin -status
TimesTen Cluster status report as of Thu Nov 11 13:59:20 2010

====================================================================
TimesTen daemon monitors:
Host:HOST1 Status: online
Host:HOST2 Status: online

====================================================================
====================================================================
TimesTen Cluster agents
Host:HOST1 Status: online
Host:HOST2 Status: online

====================================================================

Status of Cluster related to DSN MYDSN:
====================================================================
1. Status of Cluster monitoring components:
Monitor Process for Active datastore:RUNNING on Host host1
Monitor Process for Standby datastore:RUNNING on Host host2
Monitor Process for Master Datastore 1 on Host host1: RUNNING
Monitor Process for Master Datastore 2 on Host host2: RUNNING

2.Status of  Datastores comprising the cluster
Master Datastore 1:
Host:host1
Status:AVAILABLE
State:ACTIVE
Grid:NO GRID
Master Datastore 2:
Host:host2
Status:AVAILABLE
State:STANDBY
Grid:NO GRID
====================================================================
The cluster containing the replicated DSN is online

If a cache grid is configured, then the last section appears as follows:

2.Status of  Datastores comprising the cluster
Master Datastore 1:
Host:host1
Status:AVAILABLE
State:ACTIVE
Grid:AVAILABLE
Master Datastore 2:
Host:host2
Status:AVAILABLE
State:STANDBY
Grid:AVAILABLE

Message log files

The monitor processes report events and errors to the ttcwerrors.log and ttcwmsg.log files. The files are located in the daemon_home/info directory. The default size of these files is the same as the default maximum size of the user log. The maximum number of log files is the same as the default number of files for the user log. When the maximum number of files has been written, additional errors and messages overwrite the files, beginning with the oldest file.

For the default values for number of log files and log file size, see "Modifying informational messages" in Oracle TimesTen In-Memory Database Operations Guide.

9 Defining Classic Replication Schemes

This chapter describes how to define classic replication schemes.

Note:
For information about defining active standby pair replication schemes, see Chapter 3, "Defining an Active Standby Pair Replication Scheme". If you want to replicate a database that has cache groups, see Chapter 6, "Administering an Active Standby Pair with Cache Groups".

This chapter includes these topics:

- Designing a highly available system

- Defining a classic replication scheme

- Table requirements and restrictions for classic replication schemes

- Restrictions for classic replication schemes involving multiple masters

- Defining replication elements

- Checking for replication conflicts on table elements

- Setting transmit durability on DATASTORE element

- Using a return service in a classic replication scheme

- Setting STORE attributes in a classic replication scheme

- Configuring network operations for a classic replication scheme

- Classic replication scheme syntax examples

- Applying a classic replication scheme to a database

- Creating classic replication schemes with scripts

Note:
To reduce the amount of bandwidth required for replication, see "Compressing replicated traffic".
To replicate tables with columns in a different order or with a different number of partitions, see "Column definition options for replicated tables".

Designing a highly available system

These are the primary objectives of any replication scheme:

- Provide one or more backup databases to ensure that the data is always available to applications

- Provide a means to recover failed databases from their backup databases

- Distribute workloads efficiently to provide applications with the quickest possible access to the data

- Enable software upgrades and maintenance without disrupting service to users

In a highly available system, a subscriber database must be able to survive failures that may affect the master. At a minimum, the master and subscriber need to be on separate hosts. For some applications, you may want to place the subscriber in an environment that has a separate power supply. In certain cases, you may need to place a subscriber at an entirely separate site.

You can configure the following classic replication schemes (as described in "Types of replication schemes"):

- Unidirectional

- Bidirectional split workload

- Bidirectional distributed workload

- Propagation

In addition, consider whether you want to replicate a whole database or selected elements of the database. Also, consider the number of subscribers in the replication scheme. Unidirectional and propagation replication schemes enable you to choose the number of subscribers.

The rest of this section includes these topics:

- Considering failover and recovery scenarios

- Making decisions about performance and recovery tradeoffs

- Distributing workloads

For more information about using classic replication to facilitate online upgrades, see "Performing an online upgrade with replication" in the Oracle TimesTen In-Memory Database Installation Guide.

Considering failover and recovery scenarios

As you plan a replication scheme, consider every failover and recovery scenario. For example, subscriber failures generally have no impact on the applications connected to the master databases. Their recovery does not disrupt user service. If a failure occurs on a master database, you should have a means to redirect the application load to a subscriber and continue service with no or minimal interruption. This process is typically handled by a cluster manager or custom software designed to detect failures, redirect users or applications from the failed database to one of its subscribers, and manage recovery of the failed database. See Chapter 15, "Managing Database Failover and Recovery".

When planning failover strategies, consider which subscribers are to take on the role of the master and for which users or applications. Also, consider recovery factors. For example, a failed master must be able to recover its database from its most up-to-date subscriber, and any subscriber must be able to recover from its master. A bidirectional scheme that replicates the entire database can take advantage of automatic restoration of a failed master. See "Automatic catch-up of a failed master database".

Consider the failure scenario for the unidirectionally replicated database shown in Figure 9-1. In the case of a master failure, the application cannot access the database until it is recovered from the subscriber. You cannot switch the application connection or user load to the subscriber unless you use an ALTER REPLICATION statement to redefine the subscriber database as the master. See "Replacing a master database in a classic replication scheme".

Figure 9-1 Recovering a master in a unidirectional scheme

Figure 9-2 shows a bidirectional distributed workload scheme in which the entire database is replicated. Failover in this type of replication scheme involves shifting the users of the application on the failed database to the application on the surviving database. Upon recovery, the workload can be redistributed to the application on the recovered database.

Figure 9-2 Recovering a master in a distributed workload scheme

Similarly, the users in a split workload scheme must be shifted from the failed database to the surviving database. Because replication in a split workload scheme is not at the database level, you must use an ALTER REPLICATION statement to set a new master database. See "Replacing a master database in a classic replication scheme". Upon recovery, the users can be moved back to the recovered master database.

Propagation replication schemes also require the use of the ALTER REPLICATION statement to set a new master or a new propagator if the master or propagator fails. Higher availability is achieved if two propagators are defined in the replication scheme. See Figure 1-11 for an example of a propagation replication scheme with two propagators.

Making decisions about performance and recovery tradeoffs

When you design a replication scheme, weigh operational efficiencies against the complexities of failover and recovery. Factors that may complicate failover and recovery include the network topology that connects a master with its subscribers and the complexity of the replication scheme. For example, it is easier to recover a master that has been fully replicated to a single subscriber than recover a master that has selected elements replicated to different subscribers.

You can configure replication to work asynchronously (the default), "semi-synchronously" with return receipt service, or fully synchronously with return twosafe service. Selecting a return service provides greater confidence that your data is consistent on the master and subscriber databases. Your decision to use default asynchronous replication or to configure return receipt or return twosafe mode depends on the degree of confidence you require and the performance tradeoff you are willing to make in exchange.

Table 9-1 summarizes the performance and recover tradeoffs of asynchronous replication, return receipt service and return twosafe service.

Table 9-1 Performance and recovery tradeoffs

Type of behavior

Asynchronous replication (default)

Return receipt

Return twosafe

Commit sequence

Each transaction is committed first on the master database.

Each transaction is committed first on the master database

Each transaction is committed first on the subscriber database.

Performance on master

Shortest response time and best throughput because there is no log wait between transactions or before the commit on the master.

Longer response time and less throughput than asynchronous.

The application is blocked for the duration of the network round-trip after commit. Replicated transactions are more serialized than with asynchronous replication, which results in less throughput.

Longest response time and least throughput.

The application is blocked for the duration of the network round-trip and remote commit on the subscriber before the commit on the master. Transactions are fully serialized, which results in the least throughput.

Effect of a runtime error

Because the transaction is first committed on the master database, errors that occur when committing on a subscriber require the subscriber to be either manually corrected or destroyed and then recovered from the master database.

Because the transaction is first committed on the master database, errors that occur when committing on a subscriber require the subscriber to be either manually corrected or destroyed and then recovered from the master database.

Because the transaction is first committed on the subscriber database, errors that occur when committing on the master require the master to be either manually corrected or destroyed and then recovered from the subscriber database.

Failover after failure of master

If the master fails and the subscriber takes over, the subscriber may be behind the master and must reprocess data feeds and be able to remove duplicates.

If the master fails and the subscriber takes over, the subscriber may be behind the master and must reprocess data feeds and be able to remove duplicates.

If the master fails and the subscriber takes over, the subscriber is at least up to date with the master. It is also possible for the subscriber to be ahead of the master if the master fails before committing a transaction it had replicated to the subscriber.

In addition to the performance and recovery tradeoffs between the two return services, you should also consider the following:

- Return receipt can be used in more configurations, whereas return twosafe can only be used in a bidirectional configuration or an active standby pair.

- Return twosafe enables you to specify a "local action" to be taken on the master database in the event of a timeout or other error encountered when replicating a transaction to the subscriber database.

A transaction is classified as return receipt or return twosafe when the application updates a table that is configured for either return receipt or return twosafe. Once a transaction is classified as either return receipt or return twosafe, it remains so, even if the replication scheme is altered before the transaction completes.

For more information about return services, see "Using a return service in a classic replication scheme".

Distributing workloads

Consider configuring the databases to distribute application workloads and make the best use of a limited number of servers. For example, it may be efficient and economical to configure the databases in a bidirectional distributed workload replication scheme so that each serves as both master and subscriber, rather than as separate master and subscriber databases. However, a distributed workload scheme works best with applications that primarily read from the databases. Implementing a distributed workload scheme for applications that frequently write to the same elements in a database may diminish performance and require that you implement a solution to prevent or manage update conflicts, as described in Chapter 13, "Resolving Replication Conflicts".

Defining a classic replication scheme

After you have designed a classic replication scheme, use the CREATE REPLICATION SQL statement to apply the scheme to your databases. You must have the ADMIN privilege to use the CREATE REPLICATION statement.

Table 9-2 shows the components of a replication scheme and identifies the clauses associated with the topics in this chapter. The complete syntax for the CREATE REPLICATION statement is provided in Oracle TimesTen In-Memory Database SQL Reference.

Table 9-2 Components of a replication scheme

Component

See...

CREATE REPLICATION Owner.SchemeName

"Owner of the replication scheme and replicated objects"

ELEMENT ElementName ElementType

"Defining replication elements"

[CheckConflicts]

"Checking for replication conflicts on table elements"

{MASTER|PROPAGATOR} DatabaseName ON "HostName"

"Database names"

[TRANSMIT {NONDURABLE|DURABLE}]

"Setting transmit durability on DATASTORE element"

SUBSCRIBER DatabaseName ON "HostName"

"Database names"

[ReturnServiceAttribute]

"Using a return service in a classic replication scheme"

INCLUDE|EXCLUDE

"Defining the DATASTORE element"

STORE DatabaseName DataStoreAttributes

"Setting STORE attributes in a classic replication scheme"

[NetworkOperation]

"Configuring network operations for a classic replication scheme"

Note:
Naming errors in your CREATE REPLICATION statement are often hard to troubleshoot, so take the time to check and double-check the element, database, and host names for mistakes.

The replication scheme used by a database persists across system reboots. Modify a replication scheme by using the ALTER REPLICATION statement. See Chapter 10, "Altering a Classic Replication Scheme".

Owner of the replication scheme and replicated objects

The replication scheme and the replicated objects must be owned by the same user on every database in a replication scheme. To ensure that there is a common owner across all databases, you should explicitly specify the user and replication scheme in the CREATE REPLICATION statement.

For example, create a replication scheme named repscheme owned by user repl. The first line of the CREATE REPLICATION statement for repscheme is:

CREATE REPLICATION rep1.repscheme

Database names

These are the roles of the databases in a replication scheme:

- Master: Applications update the master database. The master sends the updates to the propagator or to the subscribers directly.

- Propagator: The propagator database receives updates from the master database and sends them to subscriber databases.

- Subscriber: Subscribers receive updates from the propagator or the master.

Before you define the replication scheme, you need to define the data source names (DSNs) for the databases in the replication scheme. On UNIX platforms, create an odbc.ini file. On Windows, use the ODBC Administrator to name the databases and set connection attributes. See "Step 1: Create the DSNs for the master and the subscriber" for an example.

Each database "name" specified in a replication scheme must match the prefix of the database file name without the path specified for the DataStore data store attribute in the DSN definition. Use the same name for both the DataStore and Data Source Name data store attributes in each DSN definition. If the database path is directory/subdirectory/foo.ds0, then foo is the database name that you should use. For example, this entry in an odbc.ini file shows a Data Source Name (DSN) of masterds, while the DataStore value shows the path for masterds:

[masterds]
DataStore=/tmp/masterds
DatabaseCharacterSet=AL32UTF8
ConnectionCharacterSet=AL32UTF8

Table requirements and restrictions for classic replication schemes

The name and owner of replicated tables participating in the replication scheme must be identical on the master and subscriber databases. However, the definition for the columns of replicated tables participating in the replication scheme do not necessarily need to be identical. For more information on the column definition options, see "Column definition options for replicated tables".

Replicated tables must have one of the following:

- A primary key

- A unique index over non-nullable columns

Replication uses the primary key or unique index to uniquely identify each row in the replicated table. Replication always selects the first usable index that turns up in a sequential check of the table's index array. If there is no primary key, replication selects the first unique index without NULL columns it encounters. The selected index on the replicated table in the master database must also exist on its counterpart table in the subscriber.

Note:
The keys on replicated tables are transmitted in each update record to the subscribers. Smaller keys are transmitted more efficiently.

Replicated tables have these data type restrictions:

- VARCHAR2, NVARCHAR2, VARBINARY and TT_VARCHAR columns in replicated tables is limited to a size of 4 megabytes. For a VARCHAR2 column, the maximum length when using character length semantics depends on the number of bytes each character occupies when using a particular database character set. For example, if the character set requires four bytes for each character, the maximum possible length is one million characters. For an NVARCHAR2 column, which requires two bytes for each character, the maximum length when using character length semantics is two million characters.

- Columns with the BLOB data type in replicated tables are limited to a size of 16 megabytes. Columns with the CLOB or NCLOB data type in replicated tables are limited to a size of 4 megabytes.

- A primary key column cannot have a LOB data type.

You cannot replicate tables with compressed columns.

If these requirements and restrictions present difficulties, you may want to consider using the Transaction Log API (XLA) as a replication mechanism. See "Using XLA as a replication mechanism" in Oracle TimesTen In-Memory Database C Developer's Guide.

Restrictions for classic replication schemes involving multiple masters

Designing bidirectional replication schemes are a commonly used design for classic replication. The original design for bidirectional replication was to include only two masters. However, you are not restricted in limiting your design to only two masters in your bidirectional replication design.

If you decide to use more than two masters (a multi-master topology) and if you decide to use ttRepAdmin -duplicate to duplicate another store, you must reset the replication states for the duplicated stores subscribers with the ttRepSubscriberStateSet built-in procedure to set all subscribers to the appropriate state.

As shown in Figure 9-3, you have three masters (master1, master2, and master3) each configured with a bidirectional replication scheme with each other. If you decide to re-create master2 from master1 by executing ttRepAdmin -duplicate on master1, then you must call the ttRepSubscriberStateSet built-in procedure on master2 to set the replication states for master3.

Figure 9-3 Multiple masters involved in bidirectional replication scheme

Defining replication elements

A classic replication scheme consists of one or more ELEMENT descriptions that contain the name of the element, its type (DATASTORE, TABLE, or SEQUENCE), the master database on which it is updated, and the subscriber databases to which the updates are replicated.

Note:
If you want to replicate a database with cache groups, see Chapter 6, "Administering an Active Standby Pair with Cache Groups".

These are restrictions on elements:

- Do not include a specific object (table, sequence or database) in more than one element description.

- Do not define the same element in the role of both master and propagator.

- An element must include the database on the current host as either the master, subscriber or propagator.

- Element names must be unique within a replication scheme.

The correct way to define elements in a multiple subscriber scheme is described in "Multiple subscriber classic replication schemes with return services and a log failure threshold". The correct way to propagate elements is described in "Propagation scheme".

The name of each element in a scheme can be used to identify the element if you decide later to drop or modify the element by using the ALTER REPLICATION statement.

You can add tables, sequences, and databases to an existing replication scheme. See "Altering a classic replication scheme". You can drop a table or sequence from a database that is part of a replication scheme after you exclude the table or sequence from the replication scheme. See "Dropping a table or sequence from a classic replication scheme".

The rest of this section includes the following topics:

- Defining the DATASTORE element

- Defining table elements

- Replicating tables with foreign key relationships in a classic replication scheme

- Replicating sequences

- Views and materialized views in a replicated database

Defining the DATASTORE element

To replicate the entire contents of the master database (masterds) to the subscriber database (subscriberds), the ELEMENT description (named ds1) might look like the following:

ELEMENT ds1 DATASTORE
MASTER masterds ON "system1"
SUBSCRIBER subscriberds ON "system2"

Identify a database host using the host name returned by the hostname operating system command. It is good practice to surround a host name with double quotes.

Note:
You cannot replicate a temporary database.

You can choose to exclude certain tables and sequences from the DATASTORE element by using the EXCLUDE TABLE and EXCLUDE SEQUENCE clauses of the CREATE REPLICATION statement. When you use the EXCLUDE clauses, the entire database is replicated to all subscribers in the element except for the objects that are specified in the EXCLUDE clauses. Use only one EXCLUDE TABLE and one EXCLUDE SEQUENCE clause in an element description. For example, this element description excludes two tables and one sequence:

ELEMENT ds1 DATASTORE
MASTER masterds ON "system1"
SUBSCRIBER subscriberds ON "system2"
EXCLUDE TABLE ttuser.tab1, ttuser.tab2
EXCLUDE SEQUENCE ttuser.seq1

You can choose to include only certain tables and sequences in the database by using the INCLUDE TABLE and INCLUDE SEQUENCE clauses of the CREATE REPLICATION statement. When you use the INCLUDE clauses, only the objects that are specified in the INCLUDE clauses are replicated to each subscriber in the element. Use only one INCLUDE TABLE and one INCLUDE SEQUENCE clause in an element description. For example, this element description includes one table and two sequences:

ELEMENT ds1 DATASTORE
MASTER masterds ON "system1"
SUBSCRIBER subscriberds ON "system2"
INCLUDE TABLE ttuser.tab3
INCLUDE SEQUENCE ttuser.seq2, ttuser.seq3

Defining table elements

To replicate the ttuser.tab1 and ttuser.tab2 tables from a master database (named masterds and located on a host named system1) to a subscriber database (named subscriberds on a host named system2), the ELEMENT descriptions (named a and b) might look like the following:

ELEMENT a TABLE ttuser.tab1
MASTER masterds ON "system1"
SUBSCRIBER subscriberds ON "system2"
ELEMENT b TABLE ttuser.tab2
MASTER masterds ON "system1"
SUBSCRIBER subscriberds ON "system2"

For requirements for tables in classic replication schemes, see "Table requirements and restrictions for classic replication schemes".

Replicating tables with foreign key relationships in a classic replication scheme

In a classic replication scheme, you may choose to replicate all or a subset of tables that have foreign key relationships with one another. To do so, create the tables and the foreign key relationship on each master and subscriber. Then, add the tables to the replication scheme with the ALTER REPLICATION ADD ELEMENT statement on each master and subscriber.

However, if the foreign key relationships have been configured with ON DELETE CASCADE, then you must create all of the tables before the replication scheme is created. Then, configure the replication scheme with the CREATE REPLICATION statment to include all tables with either the DATASTORE element (that does not exclude any of the tables) or the TABLE element for every table that is involved in the relationship.

You cannot add a table with a foreign key relationship configured with ON DELETE CASCADE to the replication scheme after the replication scheme is created with the ALTER REPLICATION statement. Instead, you must drop the replication scheme, create the new table with the foreign key relationship with ON DELETE CASCADE, and then create a new replication scheme that includes all of the related tables.

If a table with a foreign key configured with ON DELETE CASCADE is replicated, then the matching foreign key on the subscriber must also be configured with ON DELETE CASCADE. In addition, you must replicate any other table with a foreign key relationship to that table. This requirement prevents foreign key conflicts from occurring on subscriber tables when a cascade deletion occurs on the master database.

TimesTen replicates a cascade deletion as a single operation, rather than replicating to the subscriber each individual row deletion which occurs on the child table when a row is deleted on the parent. As a result, any row on the child table on the subscriber database, which contains the foreign key value that was deleted on the parent table, is also deleted, even if that row did not exist on the child table on the master database.

Replicating sequences

Sequences are replicated unless you exclude them from the replication scheme or unless they have the CYCLE attribute. Replication of sequences is optimized by reserving a range of sequence numbers on the standby database each time a sequence is updated on the active database. Reserving a range of sequence numbers reduces the number of updates to the transaction log. The range of sequence numbers is called a cache. Sequence updates on the active database are replicated only when they are followed by or used in replicated transactions.

Consider a sequence my.seq with a MINVALUE of 1, an INCREMENT of 1 and the default Cache of 20. The very first time that you use my.seq.NEXTVAL, the current value of the sequence on the master database is changed to 2, and a new current value of 21 (20+1) is replicated to the subscriber. The next 19 references to my.seq.NEXTVAL on the master database result in no new current value being replicated, because the current value of 21 on the subscriber database is still ahead of the current value on the master. On the twenty-first reference to my.seq.NEXTVAL, a new current value of 41 (21+20) is transmitted to the subscriber database because the subscriber's previous current value of 21 is now behind the value of 22 on the master.

Sequence replication has these restrictions:

- Sequences with the CYCLE attribute cannot be replicated.

- The definition of the replicated sequence on each peer database must be identical.

- No conflict checking is performed on sequences. If you make updates to sequences in both databases in a bidirectional replication configuration without using the RETURN TWOSAFE service, it is possible for both sequences to return the identical NEXTVAL.

If you need to use sequences in a bidirectional replication scheme where updates may occur on either peer, you may instead use a nonreplicated sequence with different MINVALUE and MAXVALUE attributes on each database to avoid conflicts. For example, you may create sequence my.seq on database DS1 with a MINVALUE of 1 and a MAXVALUE of 100, and the same sequence on DS2 with a MINVALUE of 101 and a MAXVALUE of 200. Then, if you configure DS1 and DS2 with a bidirectional replication scheme, you can make updates to either database using the sequence my.seq with the guarantee that the sequence values never conflict. Be aware that if you are planning to use ttRepAdmin -duplicate to recover from a failure in this configuration, you must drop and then re-create the sequence with a new MINVALUE and MAXVALUE after you have performed the duplicate operation.

Operations on sequences such as SELECT my.seq.NEXTVAL FROM sys.dual, while incrementing the sequence value, are not replicated until they are followed by transactions on replicated tables. A side effect of this behavior is that these sequence updates are not purged from the log until followed by transactions on replicated tables. This causes ttRepSubscriberWait and ttRepAdmin -wait to fail when only these sequence updates are present at the end of the log.

To replicate the ttuser.seq sequence from a master database (named masterds and located on a host named system1) to a subscriber database (named subscriberds on a host named system2), the element description (named a) might look like the following:

ELEMENT a SEQUENCE ttuser.seq
MASTER masterds ON "system1"
SUBSCRIBER subscriberds ON "system2"

Views and materialized views in a replicated database

A materialized view is a summary of data selected from one or more TimesTen tables, called detail tables. Although you cannot replicate materialized views directly, you can replicate their underlying detail tables in the same manner as you would replicate regular TimesTen tables.

The detail tables on the master and subscriber databases can be referenced by materialized views. However, TimesTen replication verifies only that the replicated detail tables have the same structure on both the master and subscriber. It does not enforce that the materialized views are the same on each database.

If you replicate an entire database containing a materialized or non-materialized view as a DATASTORE element, only the detail tables associated with the view are replicated. The view itself is not replicated. A matching view can be defined on the subscriber database, but is not required. If detail tables are replicated, TimesTen automatically updates the corresponding view.

Materialized views defined on replicated tables may result in replication failures or inconsistencies if the materialized view is specified so that overflow or underflow conditions occur when the materialized view is updated.

Checking for replication conflicts on table elements

When databases are configured for bidirectional replication, there is a potential for replication conflicts to occur if the same table row in two or more databases is independently updated at the same time.

Such conflicts can be detected and resolved on a table-by-table basis by including timestamps in the replicated tables and configuring the replication scheme with the optional CHECK CONFLICTS clause in each table's element description.

See Chapter 13, "Resolving Replication Conflicts" for a complete discussion on replication conflicts and how to configure the CHECK CONFLICTS clause in the CREATE REPLICATION statement.

Setting transmit durability on DATASTORE element

A master database configured for asynchronous or return receipt replication is durable by default. This means that log records are committed to disk when transactions are committed. The master database can be set to nondurable by including the TRANSMIT NONDURABLE clause in the element description.

Transaction records in the master database log buffer are, by default, flushed to disk before they are forwarded to subscribers. If the entire master database is replicated (ELEMENT is of type DATASTORE), you can improve replication performance by eliminating the master's flush-log-to-disk operation from the replication cycle. This is done by including a TRANSMIT NONDURABLE clause in the element description. The TRANSMIT setting has no effect on the subscriber. The transaction records on the subscriber database are always flushed to disk.

Master databases configured for return twosafe replication are nondurable by default and cannot be made durable. Setting TRANSMIT DURABLE on a database that is configured for return twosafe replication has no effect on return twosafe transactions.

Example 9-1 Replicating the entire master database with TRANSMIT NONDURABLE

To replicate the entire contents of the master database (masterds) to the subscriber database (subscriberds) and to eliminate the flush-log-to-disk operation, your element description (named a) might look like the following:

ELEMENT a DATASTORE
MASTER masterds ON "system1"
TRANSMIT NONDURABLE
SUBSCRIBER subscriberds ON "system2"

In general, if a master database fails, you have to initiate the ttRepAdmin -duplicate operation described in "Recovering a failed database" to recover the failed master from the subscriber database. This is always true for a master database configured with TRANSMIT DURABLE.

A database configured as TRANSMIT NONDURABLE is recovered automatically by the subscriber replication agent if it is configured in the specific type of bidirectional scheme described in "Automatic catch-up of a failed master database". Otherwise, you must follow the procedures described in "Recovering nondurable databases" to recover a failed nondurable database.

Using a return service in a classic replication scheme

You can configure your replication scheme with a return service to ensure a higher level of confidence that replicated data is consistent on both the master and subscriber databases. This section describes how to configure and manage the return receipt and return twosafe services.

You can specify a return service for table elements and database elements for any subscriber defined in a CREATE REPLICATION or ALTER REPLICATION statement.

For full details on how to configure a return service for your master and subscribers, see "Using a return service".

Setting STORE attributes in a classic replication scheme

The STORE attributes clause in either the CREATE REPLICATION and ALTER REPLICATION statements are used to set optional behavior for return services, compression, timeouts, durable commit behavior, conflict reporting, and table definition checking. For full details on how to use and configure the STORE attributes for a classic replication scheme, see "Setting STORE attributes". See "CREATE ACTIVE STANDBY PAIR" in the Oracle TimesTen In-Memory Database SQL Reference for a description of all STORE attributes.

Configuring network operations for a classic replication scheme

If your replication host has more than one network interface, you may want to configure replication to use an interface other than the default interface. For full details on how to configure more than one network interface for a classic replication scheme, see "Configuring network interfaces with the ROUTE clause".

Classic replication scheme syntax examples

The following examples in this section illustrate how to configure a variety of classic replication schemes:

- Single classic subscriber schemes

- Multiple subscriber classic replication schemes with return services and a log failure threshold

- Replicating tables to different subscribers

- Propagation scheme

- Bidirectional split workload schemes

- Bidirectional distributed workload scheme

Single classic subscriber schemes

The classic replication scheme shown in Example 9-2 is a single master and subscriber unidirectional replication scheme. The two databases are located on separate hosts, system1 and system2. We use the RETURN RECEIPT service to confirm that all transactions committed on the ttuser.tab table in the master database are received by the subscriber.

Example 9-2 Replicating one table

CREATE REPLICATION repscheme
ELEMENT e TABLE ttuser.tab
MASTER masterds ON "system1"
SUBSCRIBER subscriberds ON "system2"
RETURN RECEIPT;

The scheme shown in Example 9-3 is a single master and subscriber unidirectional replication scheme. The two databases are located on separate hosts, server1 and server2. The master database, named masterds, replicates its entire contents to the subscriber database, named subscriberds.

Example 9-3 Replicating entire database

CREATE REPLICATION repscheme
ELEMENT e DATASTORE
MASTER masterds ON "server1"
SUBSCRIBER subscriberds ON "server2";

Multiple subscriber classic replication schemes with return services and a log failure threshold

You can create a classic replication scheme that includes up to 128 subscriber databases. If you are configuring propagator databases, you can configure up to 128 propagators. Each propagator can have up to 128 subscriber databases. See "Propagation scheme" for an example of a classic replication scheme with propagator databases.

Example 9-4 Replicating to two subscribers

This example establishes a master database, named masterds, that replicates the ttuser.tab table to two subscriber databases, subscriber1ds and subscriber2ds, located on server2 and server3, respectively. The name of the classic replication scheme is twosubscribers. The name of the replication element is e.

CREATE REPLICATION twosubscribers
ELEMENT e TABLE ttuser.tab
MASTER masterds ON "server1"
SUBSCRIBER subscriber1ds ON "server2",
subscriber2ds ON "server3";

Example 9-5 Replicating to two subscribers with RETURN RECEIPT

This example uses the basic example in Example 9-4 and adds a RETURN RECEIPT attribute and a STORE parameter. RETURN RECEIPT enables the return receipt service for both databases. The STORE parameter sets a FAILTHRESHOLD value of 10 to establish the maximum number of transaction log files that can accumulate on masterds for a subscriber before it assumes the subscriber has failed.

CREATE REPLICATION twosubscribers
ELEMENT e TABLE ttuser.tab
MASTER masterds ON "server1"
SUBSCRIBER subscriber1ds ON "server2",
subscriber2ds ON "server3"
RETURN RECEIPT
STORE masterds FAILTHRESHOLD 10;

Example 9-6 Enabling RETURN RECEIPT for only one subscriber

This example shows how to enable RETURN RECEIPT for only subscriber2ds. Note that there is no comma after the subscriber1ds definition.

CREATE REPLICATION twosubscribers
ELEMENT e TABLE ttuser.tab
MASTER masterds ON "server1"
SUBSCRIBER subscriber1ds ON "server2"
SUBSCRIBER subscriber2ds ON "server3" RETURN RECEIPT
STORE masterds FAILTHRESHOLD 10;

Example 9-7 Enabling different return services for subscribers

This example shows how to apply RETURN RECEIPT BY REQUEST to subscriber1ds and RETURN RECEIPT to subscriber2ds. In this classic replication scheme, applications accessing subscriber1ds must use the ttRepSyncSet procedure to enable the return services for a transaction, while subscriber2ds unconditionally provides return services for all transactions.

CREATE REPLICATION twosubscribers
ELEMENT e TABLE ttuser.tab
MASTER masterds ON "server1"
SUBSCRIBER subscriberds1 ON "server2" RETURN RECEIPT BY REQUEST
SUBSCRIBER subscriber2ds ON "server3" RETURN RECEIPT
STORE masterds FAILTHRESHOLD 10;

Replicating tables to different subscribers

The classic replication scheme shown in Example 9-8 establishes a master database, named centralds, that replicates four tables. ttuser.tab1 and ttuser.tab2 are replicated to the subscriber backup1ds. ttuser.tab3 and ttuser.tab4 are replicated to backup2ds. The master database is located on the finance server. Both subscribers are located on the backupsystem server.

Example 9-8 Replicating tables to different subscribers

CREATE REPLICATION twobackups
ELEMENT a TABLE ttuser.tab1
MASTER centralds ON "finance"
SUBSCRIBER backup1ds ON "backupsystem"
ELEMENT b TABLE ttuser.tab2
MASTER centralds ON "finance"
SUBSCRIBER backup1ds ON "backupsystem"
ELEMENT d TABLE ttuser.tab3
MASTER centralds ON "finance"
SUBSCRIBER backup2ds ON "backupsystem"
ELEMENT d TABLE ttuser.tab4
MASTER centralds ON "finance"
SUBSCRIBER backup2ds ON "backupsystem";

Propagation scheme

In Example 9-9, the master database sends updates on a table to a propagator that forwards the changes to two subscribers. The master database is centralds on the finance host. The propagator database is propds on the nethandler host. The subscribers are backup1ds on backupsystem1 and backup2ds on backupsystem2.

The classic replication scheme has two elements. For element a, the changes to the tab table on centralds are replicated to the propds propagator database. For element b, the changes to the tab table received by propds are replicated to the two subscribers, backup1ds and backup2ds.

Example 9-9 Propagation

CREATE REPLICATION propagator
ELEMENT a TABLE ttuser.tab
MASTER centralds ON "finance"
SUBSCRIBER propds ON "nethandler"
ELEMENT b TABLE ttuser.tab
PROPAGATOR propds ON "nethandler"
SUBSCRIBER backup1ds ON "backupsystem1",
backup2ds ON "backupsystem2";

Bidirectional split workload schemes

In Example 9-10, there are two databases, westds on the westcoast host and eastds on the eastcoast host. Customers are represented in two tables: waccounts contains data for customers in the Western region and eaccounts has data for customers from the Eastern region. The westds database updates the waccounts table and replicates it to the eastds database. The eaccounts table is owned by the eastds database and is replicated to the westds database. The RETURN RECEIPT attribute enables the return receipt service to guarantee that transactions on either master table are received by their subscriber.

Example 9-10 Bidirectional split workload

CREATE REPLICATION r1
ELEMENT elem_waccounts TABLE ttuser.waccounts
MASTER westds ON "westcoast"
SUBSCRIBER eastds ON "eastcoast" RETURN RECEIPT
ELEMENT elem_eaccounts TABLE ttuser.eaccounts
MASTER eastds ON "eastcoast"
SUBSCRIBER westds ON "westcoast" RETURN RECEIPT;

Bidirectional distributed workload scheme

Example 9-11 shows a bidirectional general workload classic replication scheme in which the ttuser.accounts table can be updated on either the eastds or westds database. Each database is both a master and a subscriber for the accounts table.

Note:
Do not use a bidirectional distributed workload replication scheme with return twosafe return service.

Example 9-11 Bidirectional distributed workload scheme

CREATE REPLICATION r1
ELEMENT elem_accounts_1 TABLE ttuser.accounts
MASTER westds ON "westcoast"
SUBSCRIBER eastds ON "eastcoast"
ELEMENT elem_accounts_2 TABLE ttuser.accounts
MASTER eastds ON "eastcoast"
SUBSCRIBER westds ON "westcoast";

When elements are replicated in this manner, the applications should write to each database in a coordinated manner to avoid simultaneous updates on the same data. To manage update conflicts, include a timestamp column of type BINARY(8) in the replicated table and enable timestamp comparison by including the CHECK CONFLICTS clause in the CREATE REPLICATION statement. See Chapter 13, "Resolving Replication Conflicts" for a complete discussion on how to manage update conflicts.

Example 9-12 shows that the tstamp timestamp column is included in the ttuser.accounts table. The CREATE REPLICATION statement has been modified to include the CHECK CONFLICTS clause.

Example 9-12 Managing update conflicts

CREATE TABLE ttuser.accounts (custname VARCHAR2(30) NOT NULL,
address VARCHAR2(80),
curbalance DEC(15,2),
tstamp BINARY(8),
PRIMARY KEY (custname));

CREATE REPLICATION r1
ELEMENT elem_accounts_1 TABLE ttuser.accounts
CHECK CONFLICTS BY ROW TIMESTAMP
COLUMN tstamp
UPDATE BY SYSTEM
ON EXCEPTION ROLLBACK WORK
MASTER westds ON "westcoast"
SUBSCRIBER eastds ON "eastcoast"
ELEMENT elem_accounts_2 TABLE ttuser.accounts
CHECK CONFLICTS BY ROW TIMESTAMP
COLUMN tstamp
UPDATE BY SYSTEM
ON EXCEPTION ROLLBACK WORK
MASTER eastds ON "eastcoast"
SUBSCRIBER westds ON "westcoast";

Applying a classic replication scheme to a database

When you define the classic replication scheme, save the CREATE REPLICATION statement in a SQL file. After you have described the classic replication scheme in a SQL file, you can execute the SQL on the database using the -f option to the ttIsql utility. The syntax is:

ttIsql -f schemefile.sql -connstr "dsn=DSN"

Example 9-13 Creating a classic replication scheme by executing a SQL file

If your classic replication scheme is described in a file called repscheme.sql, you can execute the file on a DSN, called masterDSN, by entering:

> ttIsql -f repscheme.sql -connstr "dsn=masterDSN"

Under most circumstances, you should apply the same scheme to all of the replicated databases. You must invoke a separate ttIsql command on each host to apply the classic replication scheme.

Example 9-14 Executing a SQL file on each host

If your classic replication scheme includes the databases masterDSN on host S1, subscriber1DSN on host S2, and subscriber2DSN on host S3, do the following:

On host S1, enter:

> ttIsql -f repscheme.sql -connstr "dsn=masterDSN"

On host S2, enter:

> ttIsql -f repscheme.sql -connstr "dsn=subscriber1DSN"

On host S3, enter:

> ttIsql -f repscheme.sql -connstr "dsn=subscriber2DSN"

You can also execute the SQL file containing your classic replication scheme from the ttIsql command line after connecting to a database. For example:

Command> run repscheme.sql;

Creating classic replication schemes with scripts

Creating your classic replication schemes with scripts can save you time and help you avoid mistakes. This section provides some suggestions for automating the creation of replication schemes using Perl.

Consider the general workload bidirectional scheme shown in Example 9-15. Entering the element description for the five tables, ttuser.accounts, ttuser.sales, ttuser.orders, ttuser.inventory, and ttuser.customers, would be tedious and error-prone if done manually.

Example 9-15 General workload bidirectional replication scheme

CREATE REPLICATION bigscheme
ELEMENT elem_accounts_1 TABLE ttuser.accounts
MASTER westds ON "westcoast"
SUBSCRIBER eastds ON "eastcoast"
ELEMENT elem_accounts_2 TABLE ttuser.accounts
MASTER eastds ON "eastcoast"
SUBSCRIBER westds ON "westcoast"
ELEMENT elem_sales_1 TABLE ttuser.sales
MASTER westds ON "westcoast"
SUBSCRIBER eastds ON "eastcoast"
ELEMENT elem_sales_2 TABLE ttuser.sales
MASTER eastds ON "eastcoast"
SUBSCRIBER westds ON "westcoast"
ELEMENT elem_orders_1 TABLE ttuser.orders
MASTER westds ON "westcoast"
SUBSCRIBER eastds ON "eastcoast"
ELEMENT elem_orders_2 TABLE ttuser.orders
MASTER eastds ON "eastcoast"
SUBSCRIBER westds ON "westcoast"
ELEMENT elem_inventory_1 TABLE ttuser.inventory
MASTER westds ON "westcoast"
SUBSCRIBER eastds ON "eastcoast"
ELEMENT elem_inventory_2 TABLE ttuser.inventory
MASTER eastds ON "eastcoast"
SUBSCRIBER westds ON "westcoast"
ELEMENT elem_customers_1 TABLE ttuser.customers
MASTER westds ON "westcoast"
SUBSCRIBER eastds ON "eastcoast"
ELEMENT elem_customers_2 TABLE ttuser.customers
MASTER eastds ON "eastcoast"
SUBSCRIBER westds ON "westcoast";

It is often more convenient to automate the process of writing a classic replication scheme with scripting. For example, the perl script shown in Example 9-16 can be used to build the scheme shown in Example 9-15.

Example 9-16 Using a Perl script to create a replication scheme

@tables = qw(
ttuser.accounts
ttuser.sales
ttuser.orders
ttuser.inventory
ttuser.customers
);

print "CREATE REPLICATION bigscheme";

foreach $table (@tables) {
$element = $table;
$element =~ s/repl\./elem\_/;

print "\n";
print " ELEMENT $element\_1 TABLE $table\n";
print " MASTER westds ON \"westcoast\"\n";
print " SUBSCRIBER eastds ON \"eastcoast\"\n";
print " ELEMENT $element\_2 TABLE $table\n";
print " MASTER eastds ON \"eastcoast\"\n";
print " SUBSCRIBER westds ON \"westcoast\"";
}
print ";\n";

The @tables array shown in Example 9-16 can be obtained from some other source, such as a database. For example, you can use ttIsql and f in a Perl statement to generate a @tables array for all of the tables in the WestDSN database with the owner name repl:

@tables = 'ttIsql -e "tables; quit" WestDSN
| grep " REPL\."';

Example 9-17 shows a modified version of the script in Example 9-16 that creates a classic replication scheme for all of the repl tables in the WestDSN database. (Note that some substitution may be necessary to remove extra spaces and line feeds from the grep output.)

Example 9-17 Perl script to create a replication scheme for all tables in WestDSN

@tables = 'ttIsql -e "tables; quit" WestDSN
| grep " REPL\."';

print "CREATE REPLICATION bigscheme";

foreach $table (@tables) {
$table =~ s/^\s*//; # Remove extra spaces
$table =~ s/\n//; # Remove line feeds
$element = $table;
$element =~ s/repl\./elem\_/;

print "\n";
print " ELEMENT $element\_1 TABLE $table\n";
print " MASTER westds ON \"westcoast\"\n";
print " SUBSCRIBER eastds ON \"eastcoast\"\n";
print " ELEMENT $element\_2 TABLE $table\n";
print " MASTER eastds ON \"eastcoast\"\n";
print " SUBSCRIBER westds ON \"westcoast\"";
}
print ";\n";

10 Altering a Classic Replication Scheme

This chapter describes how to alter an existing classic replication system.

- Altering a classic replication scheme

- Altering a replicated table in a classic replication scheme

- Truncating a replicated table in a classic replication scheme

- Dropping a classic replication scheme

Table 10-1 lists the tasks often performed on an existing classic replicated system.

Table 10-1 Tasks performed on an existing classic replicated system

Task

What to do

Alter or drop a classic replication scheme

See"Altering a classic replication scheme" and "Dropping a classic replication scheme".

Alter a table used in a replication scheme

See "Altering a replicated table in a classic replication scheme".

Truncate a table used in a replication scheme

See "Truncating a replicated table in a classic replication scheme".

Change the replication state of a subscriber database

See "Setting the replication state of subscribers".

Resolve update conflicts

See Chapter 13, "Resolving Replication Conflicts".

Recover from failures

See Chapter 15, "Managing Database Failover and Recovery".

Upgrade database

Use the ttMigrate and ttRepAdmin utilities, as described in "Database Upgrades" in Oracle TimesTen In-Memory Database Installation Guide.

Altering a classic replication scheme

You can perform the following tasks without stopping the replication agent:

- Create, alter or drop a user. These statements are replicated.

- Grant or revoke privileges from a user. These statements are replicated.

- Add a subscriber to the replication scheme. See "Creating and adding a subscriber database to a classic replication scheme".

- Add a PL/SQL object to the master database and implement its replication on subscribers. See "Adding a PL/SQL object to an existing classic replication scheme".

Use ALTER REPLICATION to alter the classic replication scheme on the master and subscriber databases. Any alterations on the master database must also be made on its subscribers.

Note:
You must have the ADMIN privilege to use the ALTER REPLICATION statement.

Most ALTER REPLICATION operations are supported only when the replication agent is stopped (ttAdmin -repStop). The procedure for ALTER REPLICATION operations that require the replication agents to be stopped is:

1. Use the ttRepStop built-in procedure or ttAdmin -repStop to stop the replication agent for the master and subscriber databases. While the replication agents are stopped, changes to the master database are stored in the log.

2. Issue the same ALTER REPLICATION statement on both master and subscriber databases.

3. Use the ttRepStart built-in procedure or ttAdmin -repStart to restart the replication agent for the master and subscriber databases. The changes stored in the master database log are sent to the subscriber database.

If you use ALTER REPLICATION to change a classic replication scheme that specifies a DATASTORE element, then:

- You cannot use SET NAME to change the name of the DATASTORE element.

- You cannot use SET CHECK CONFLICTS to enable conflict resolution.

This section includes the following topics:

- Adding a table or sequence to an existing classic replication scheme

- Adding a PL/SQL object to an existing classic replication scheme

- Adding a DATASTORE element to an existing classic replication scheme

- Dropping a table or sequence from a classic replication scheme

- Creating and adding a subscriber database to a classic replication scheme

- Dropping a subscriber database from a classic replication scheme

- Changing a TABLE or SEQUENCE element name in a classic replication scheme

- Replacing a master database in a classic replication scheme

- Eliminating conflict detection in a classic replication scheme

- Eliminating the return receipt service in a classic replication scheme

- Changing the port number for a classic replication scheme

- Changing the replication route

- Changing the log failure threshold

Adding a table or sequence to an existing classic replication scheme

There are two ways to add a table or sequence to an existing classic replication scheme:

- When the element level of the classic replication scheme is TABLE or SEQUENCE, use the ALTER REPLICATION statement with the ADD ELEMENT clause to add a table or sequence. See Example 10-1.

- When the element level of the classic replication scheme is DATASTORE, use the ALTER REPLICATION statement with the ALTER ELEMENT clause to include a table or sequence. See Example 10-2.

Example 10-1 Adding a sequence and a table to a classic replication scheme

This example uses the classic replication scheme r1 that was defined in Example 9-10. It alters replication scheme r1 to add sequence seq and table westleads, which are updated on database westds and replicated to database eastds.

ALTER REPLICATION r1
ADD ELEMENT elem_seq SEQUENCE seq
MASTER westds ON "westcoast"
SUBSCRIBER eastds ON "eastcoast"
ADD ELEMENT elem_westleads TABLE westleads
MASTER westds ON "westcoast"
SUBSCRIBER eastds ON "eastcoast";

Example 10-2 Adding a sequence and a table to a DATASTORE element

Add the sequence my.seq and the table my.tab1 to the ds1 DATASTORE element in my.rep1 replication scheme.

ALTER REPLICATION my.rep1
ALTER ELEMENT ds1 DATASTORE
INCLUDE SEQUENCE my.seq
ALTER ELEMENT ds1 DATASTORE
INCLUDE TABLE my.tab1;

Adding a PL/SQL object to an existing classic replication scheme

To add a new PL/SQL procedure, package, package body or function to an existing replication scheme, complete these tasks:

1. Create the PL/SQL object on a master database. The CREATE statement is not replicated to subscribers.

2. Create the PL/SQL object on the subscribers

3. Grant privileges to the new PL/SQL object on the master database. The GRANT statement is replicated to the subscribers.

Adding a DATASTORE element to an existing classic replication scheme

You can add a DATASTORE element to an existing classic replication scheme by using the ALTER REPLICATION statement with the ADD ELEMENT clause. All tables except temporary tables, materialized views, and nonmaterialized views are included in the replication scheme if you do not use the INCLUDE or EXCLUDE clauses. See "Including tables or sequences when you add a DATASTORE element" and "Excluding a table or sequence when you add a DATASTORE element".

Example 10-3 Adding a DATASTORE element to a classic replication scheme

Add a DATASTORE element to an existing classic replication scheme.

ALTER REPLICATION my.rep1
ADD ELEMENT ds1 DATASTORE
MASTER rep2
SUBSCRIBER rep1, rep3;

Including tables or sequences when you add a DATASTORE element

You can restrict replication to specific tables or sequences when you add a database to an existing classic replication scheme. Use the ALTER REPLICATION statement with the ADD ELEMENT clause and the INCLUDE TABLE clause or INCLUDE SEQUENCE clause. You can have one INCLUDE clause for each table or sequence in the same ALTER REPLICATION statement.

Example 10-4 Including a table and sequence in a DATASTORE element

Add the ds1 DATASTORE element to my.rep1 replication scheme. Include the table my.tab2 and the sequence my.seq in the DATASTORE element.

ALTER REPLICATION my.rep1
ADD ELEMENT ds1 DATASTORE
MASTER rep2
SUBSCRIBER rep1, rep3
INCLUDE TABLE my.tab2
INCLUDE SEQUENCE my.seq;

Excluding a table or sequence when you add a DATASTORE element

You can exclude tables or sequences when you add a DATASTORE element to an existing classic replication scheme. Use the ALTER REPLICATION statement with the ADD ELEMENT clause and the EXCLUDE TABLE clause or EXCLUDE SEQUENCE clause. You can have one EXCLUDE clause for each table or sequence in the same ALTER REPLICATION statement.

Example 10-5 Excluding a table or sequence from a DATASTORE element

Add the ds2 DATASTORE element to a replication scheme, but exclude the table my.tab1 and the sequence my.seq.

ALTER REPLICATION my.rep1
ADD ELEMENT ds2 DATASTORE
MASTER rep2
SUBSCRIBER rep1
EXCLUDE TABLE my.tab1
EXCLUDE SEQUENCE my.seq;

Dropping a table or sequence from a classic replication scheme

This section includes the following topics:

- Dropping a table or sequence that is replicated as part of a DATASTORE element

- Dropping a table or sequence that is replicated as a TABLE or SEQUENCE element

Dropping a table or sequence that is replicated as part of a DATASTORE element

To drop a table or sequence that is part of a classic replication scheme at the DATASTORE level, complete the following tasks:

1. Stop the replication agent.

2. Exclude the table or sequence from the DATASTORE element in the classic replication scheme.

3. Drop the table or sequence.

If you have more than one DATASTORE element that contains the table or sequence, then you must exclude the table or sequence from each element before you drop it.

Example 10-6 Excluding a table from a DATASTORE element and then dropping the table

Exclude the table my.tab1 from the ds1 DATASTORE element in the my.rep1 replication scheme. Then drop the table.

ALTER REPLICATION my.rep1
ALTER ELEMENT ds1 DATASTORE
EXCLUDE TABLE my.tab1;
DROP TABLE my.tab1;

Dropping a table or sequence that is replicated as a TABLE or SEQUENCE element

To drop a table that is part of a classic replication scheme at the TABLE or SEQUENCE level, complete the following tasks:

1. Stop the replication agent.

2. Drop the element from the classic replication scheme.

3. Drop the table or sequence.

Example 10-7 Dropping an element from a classic replication scheme and then dropping the sequence

Drop the SEQUENCE element elem_seq from the classic replication scheme r1. Then drop the sequence seq.

ALTER REPLICATION r1
DROP ELEMENT elem_seq;
DROP SEQUENCE seq;

Creating and adding a subscriber database to a classic replication scheme

You can add a new subscriber database while the replication agents are running. To add a database to a classic replication scheme, do the following:

1. Make sure the new subscriber database does not exist.

2. Apply the appropriate statements to all participating databases:

ALTER REPLICATION ...
ALTER ELEMENT ...
ADD SUBSCRIBER ...

3. On the source database (the master), create a user and grant the ADMIN privilege to the user:

CREATE USER ttuser IDENTIFIED BY ttuser;
User created.

GRANT admin TO ttuser;

4. Logged in as the instance administrator, run the ttRepAdmin -duplicate command to copy the contents of the master database to the newly created subscriber. You can use the -setMasterRepStart option to ensure that any updates made to the master after the duplicate operation has started are also copied to the subscriber.

5. Start the replication agent on the newly created database (ttAdmin -repStart).

Example 10-8 Adding a subscriber to a replicated table

This example alters the r1 replication scheme to add a subscriber (backup3) to the westleads table (step 2 above):

ALTER REPLICATION r1
ALTER ELEMENT elem_westleads
ADD SUBSCRIBER backup3 ON "backupserver";

Dropping a subscriber database from a classic replication scheme

Stop the replication agent before you drop a subscriber database.

This example alters the r1 replication scheme to drop the backup3 subscriber for the westleads table:

Example 10-9 Dropping a subscriber for a replicated table

ALTER REPLICATION r1
ALTER ELEMENT elem_westleads
DROP SUBSCRIBER backup3 ON "backupserver";

Changing a TABLE or SEQUENCE element name in a classic replication scheme

Stop the replication agent before you change a TABLE or SEQUENCE element name in a classic replication scheme.

Change the element name of the westleads table from elem_westleads to newelname:

Example 10-10 Changing a table name

ALTER REPLICATION r1
ALTER ELEMENT Eelem_westleads
SET NAME newelname;

Note:
You cannot use the SET NAME clause to change the name of a DATASTORE element.

Replacing a master database in a classic replication scheme

Stop the replication agent before you replace a master database in a classic replication scheme.

In this example, newwestds is made the new master for all elements currently configured for the master, westds:

Example 10-11 Replacing a master database in a classic replication scheme

ALTER REPLICATION r1
ALTER ELEMENT * IN westds
SET MASTER newwestds;

Eliminating conflict detection in a classic replication scheme

In this example, conflict detection configured by the CHECK CONFLICTS clause in the classic replication scheme shown in Example 13-2 is eliminated for the elem_accounts_1 table:

Example 10-12 Eliminating conflict detection for a table

ALTER REPLICATION r1
ALTER ELEMENT elem_accounts_1
SET NO CHECK;

See Chapter 13, "Resolving Replication Conflicts" for a detailed discussion on conflict checking.

Eliminating the return receipt service in a classic replication scheme

In this example, the return receipt service is eliminated for the first subscriber in the classic replication scheme shown in Example 9-10:

Example 10-13 Eliminating return receipt service for a subscriber

ALTER REPLICATION r1
ALTER ELEMENT elem_waccounts
ALTER SUBSCRIBER eastds ON "eastcoast"
SET NO RETURN;

Changing the port number for a classic replication scheme

The port number is the TCP/IP port number on which the replication agent of a subscriber database accepts connection requests from the master replication agent. See "Port assignments" for details on how to assign port to the replication agents.

In this example, the r1 replication scheme is altered to change the port number of the eastds to 22251:

Example 10-14 Changing a port number for a database

ALTER REPLICATION r1
ALTER STORE eastds ON "eastcoast"
SET PORT 22251;

Changing the replication route

If a replication host has multiple network interfaces, you may specify which interfaces are used for replication traffic using the ROUTE clause. If you need to change which interfaces are used by replication, you may do so by dropping and adding IP addresses from or to a ROUTE clause. See "Configuring network interfaces with the ROUTE clause" for more information.

Changing the log failure threshold

Use the FAILTHRESHOLD attribute of the STORE parameter to reset the log failure threshold. Stop the replication agents before using ALTER REPLICATION to define a new threshold value, and then restart the replication agents.

See "Setting the transaction log failure threshold" for more information about the log failure threshold.

Altering a replicated table in a classic replication scheme

You can use ALTER TABLE ... ADD COLUMN or ALTER TABLE ... DROP COLUMN statements to add or drop columns on the master database in a classic replication scheme. The ALTER TABLE operation is replicated to alter the subscriber databases. These are the only ALTER TABLE clauses that are replicated in a classic replication scheme.

If you use ALTER TABLE on a database configured for bidirectional replication, first stop updates to the table on all of the replicated databases and confirm all replicated updates to the table have been received by the databases before issuing the ALTER TABLE statement. Do not resume updates until the ALTER TABLE operation has been replicated to all databases. This is necessary to ensure that there are no write operations until after the table is altered on all databases.

Note:
You can use the ttRepSubscriberWait built-in procedure or monitoring tools described in Chapter 12, "Monitoring Replication" to confirm the updates have been received and committed on the databases.

Also, if you are executing a number of successive ALTER TABLE operations on a database, you should only proceed with the next ALTER TABLE after you have confirmed the previous ALTER TABLE has reached all of the subscribers.

Note:
You can use the ALTER TABLE statement to change default column values, but the ALTER TABLE statement is not replicated. Thus, default column values need not be identical on all nodes.

Truncating a replicated table in a classic replication scheme

You can use TRUNCATE TABLE to delete all of the rows of a table without dropping the table itself. Truncating a table is faster than using a DELETE FROM table statement.

Truncate operations on replicated tables are replicated and result in truncating the table on the subscriber database. Unlike delete operations, however, the individual rows are not deleted. Even if the contents of the tables do not match at the time of the truncate operation, the rows on the subscriber database are deleted anyway.

The TRUNCATE statement replicates to the subscriber, even when no rows are operated upon.

When tables are being replicated with timestamp conflict checking enabled, conflicts are not reported.

Dropping a classic replication scheme

You can use the DROP REPLICATION statement to remove a replication scheme from a database. You cannot drop a classic replication scheme when master catchup is required unless it is the only classic replication scheme in the database.

Note:
You must have the ADMIN privilege to use the DROP REPLICATION statement.

You must stop the replication agent before you drop a classic replication scheme.

Example 10-15 Dropping a replication scheme

To remove the repscheme replication scheme from a database, enter the following:

DROP REPLICATION repscheme;

If you are dropping replicated tables, you must drop the classic replication scheme before dropping the replicated tables. Otherwise, you receive an error indicating that you have attempted to drop a replicated table or index.

Example 10-16 Removing a table and a classic replication scheme from a database

To remove the tab table and repscheme replication scheme from a database, enter the following:

DROP REPLICATION repscheme;
DROP TABLE tab;

11 Setting Up a Replicated System

This chapter describes how to set up and start replication.

- Setting up the replication environment

- Duplicating a master database to a subscriber

- Configuring a large number of subscribers

- Replicating databases across releases

- Starting and stopping the replication agents

- Setting the replication state of subscribers

Setting up the replication environment

The following sections describe how to set up your replication environment:

- Establishing the databases

- Connection attributes for replicated databases

- Configuring parallel replication

- Managing the transaction log on a replicated database

Establishing the databases

You can replicate one or more tables on any existing database. If the database you want to replicate does not yet exist, you must first create one, as described in "Managing TimesTen Databases" in Oracle TimesTen In-Memory Database Operations Guide.

After you have identified or created the master database, create a DSN definition for the subscriber database on the target host. Set the connection attributes for the master and subscriber databases as described in "Connection attributes for replicated databases".

After you have defined the DSN for the subscriber, you can populate the subscriber database with the tables to be replicated from the master in one of two ways:

- Connect to the database and use SQL statements to create new tables in the subscriber database that match those to be replicated from the master.

- Use the ttRepAdmin -duplicate utility to copy the entire contents of the master database to the subscriber. See "Duplicating a master database to a subscriber".

Connection attributes for replicated databases

Databases that replicate to each other must have the same DatabaseCharacterSet data store attribute. TimesTen does not perform any character set conversion between replicated databases.

If you want to configure parallel replication, see "Configuring parallel replication" for information about setting the ReplicationParallelism and ReplicationApplyOrdering data store attributes.

See "Setting connection attributes for logging" for recommendations for managing the replication log files.

It is possible to replicate between databases with different settings for the TypeMode data store attribute. However, you must make sure that the underlying data type for each replicated column is the same on each node. See "TypeMode" in Oracle TimesTen In-Memory Database Reference for more information.

In an active standby pair, use the ReceiverThreads first connection attribute to increase the number of threads that apply changes from the active database to the standby database from 1 to 2. If you set ReceiverThreads to 2 on the standby, you should also set it to 2 on the active to maintain increased throughput if there is a failover.

You can also set ReceiverThreads to 2 on one or more read-only subscribers in an active standby pair to increase replication throughput from the standby database.

Databases must be hosted on systems that have two or more CPUs to take advantage of setting this attribute to 2.

Configuring parallel replication

By default, replication is performed with a single thread where the nodes in a replication scheme have one log reader, or transmitter thread, on the source database, and one applier, or receiving thread, on the target database. You can increase your performance by configuring parallel replication, which configures multiple threads for sending updates from the source database to the target database and for applying the updates on the target database. These threads act in parallel to replicate and apply transactional changes to nodes in a replication scheme. By default, parallel replication enforces transactional dependencies and applies changes in commit order; however, you can disable enforcement of the commit order.

Note:
If you enable parallel replication, you cannot execute both DDL and DML statements in the same transaction.

Parallel replication options:

- Automatic parallel replication: Parallel replication over multiple threads that automatically enforces transactional dependencies and all changes applied in commit order. This is the default.

- Automatic parallel replication with disabled commit dependencies: Parallel replication over multiple threads that automatically enforces transactional dependencies, but does not enforce transactions to be committed in the same order on the subscriber database as on the master database.

- User-defined parallel replication: For applications that use a classic replication scheme, have very predictable transactional dependencies, and do not require that the commit order on the receiver is the same as that on the originating database. You can specify the number of transaction tracks and apply specific transactions to each track. All tracks are read, transmitted and applied in parallel.

These options are configured with the ReplicationApplyOrdering and ReplicationParallelism data store creation attributes, which must be set when the database is created.

Note:
All databases within the replication scheme that use parallel replication must be configured identically with the same type of parallel replication and the same number of threads or tracks.
The only time you can have different values for parallel replication attributes is during an upgrade. For details, see "Upgrades when using parallel replication" in the Oracle TimesTen In-Memory Database Installation Guide.

The following sections describe the options for parallel replication:

- Configuring automatic parallel replication

- Configuring automatic parallel replication with disabled commit dependencies

- Configuring user-defined parallel replication for classic replication schemes

Configuring automatic parallel replication

Automatic parallel replication enables you to configure multiple threads that act in parallel to replicate and apply transactional changes to nodes in either a classic or an active standby pair replication scheme. Automatic parallel replication enforces transactional dependencies and applies changes in commit order.

Enable automatic parallel replication by setting these data store attributes at database creation time:

- Set ReplicationApplyOrdering=0, which is also the default.

- Set ReplicationParallelism to a number from 2 to 32. The number cannot exceed half the value of LogBufParallelism. This number indicates the number of transmitter threads on the source database and the number of receiver threads on the target database. However, if you are using single-threaded replication, set ReplicationParallelism to 1, which is also the default.

Note:
If ReplicationParallelism is greater than 1, the LogBufParallelism first connection attribute must be an integral multiple of ReplicationParallelism.

If the replication scheme is an active standby pair that replicates AWT cache groups, the settings for ReplicationApplyOrdering, ReplicationParallelism, and the CacheAWTParallelism data store attributes determine how many threads are used to apply changes in the TimesTen cache tables to the corresponding Oracle database tables. See "Configuring parallel propagation to the Oracle database tables" in Oracle TimesTen Application-Tier Database Cache User's Guide for more information.

For more information on these data store attributes, see "ReplicationParallelism", "ReplicationApplyOrdering", and "LogBufParallelism" in the Oracle TimesTen In-Memory Database Reference.

Configuring automatic parallel replication with disabled commit dependencies

In order to enforce transactional dependencies and ensure that changes are applied in commit order, automatic parallel replication normally tracks:

- Begin dependencies: Operations that force one transaction to execute before another, such as an insert of a row followed by a delete of that same row.

- Commit dependencies: Order in which transactions are committed so that they are committed on a subscriber in the same order as on the master database.

While parallel replication improves performance by utilizing multiple threads, you can further increase throughput performance when using automatic parallel replication if the transactions do not require enforcement of commit dependencies. That is, if your application has predictable transactional dependencies and does not require the commit order on the target database be the same as the order on the source database, you can relax the enforcement of the commit dependencies and still maintain transactional correctness. For example, if separate transactions are working on separate tables, you do not need to enforce commit dependencies.

By relaxing the requirement for tracking commit dependencies, you can improve the performance for automatic parallel replication. When you do not enforce commit dependencies, all non-DDL transactions may commit on the subscribers in a different order than how they were originally executed on the master. Begin dependencies are always enforced to prevent apply order anomalies.

You can only disable commit dependencies for automatic parallel replication for an active standby pair that uses asynchronous replication and does not contain cache groups. You can set the following data store attributes at database creation time:

- Set the ReplicationApplyOrdering=2 before you create the TimesTen database.

- Set ReplicationParallelism to a number from 2 to 32. The number cannot exceed half the value of LogBufParallelism. This number indicates the number of transmitter threads on the source database and the number of receiver threads on the target database. However, if you are using single-threaded replication, set ReplicationParallelism to 1, which is also the default.

Note:
If ReplicationParallelism is greater than 1, the LogBufParallelism first connection attribute must be an integral multiple of ReplicationParallelism.

However, while your performance improves, this option requires the use of additional space in the temporary region of 16 MB plus an additional 16 MB for each configured replication track (ReplicationParallelism connection attribute setting). For example, if the ReplicationParallism connection attribute is set to 10, then this feature requires 16 MB + 160 MB = 176 MB of additional temporary region space.

When you use automatic parallel replication and disable commit dependencies, some of the tracks may move ahead of the others. This is known as a drift between the parallel replication tracks. You can limit the amount of drift between the replication tracks by setting the ParReplMaxDrift configuration parameter within the ttDbConfig built-in procedure.

Call ttDbConfig("ParReplMaxDrift", "30");

The example sets the allowed drift to 30 seconds between the replication tracks, after which TimesTen causes all replication tracks to catch up to each other. For more details, see "ttDBConfig" in the Oracle TimesTen In-Memory Database Reference.

Specifying replication tracks within an automatic parallel replication environment

In general, automatic parallel replication decides over which thread (track) to replicate each transaction from the master to the subscriber. Thus, you do not have to manually decide how to divide work across different tracks.

However, with dependent transactions, you may achieve better performance by manually assigning them to the same track. Thus, the application has the option to specify which track a transaction belongs to when the transaction starts on the source database with either the ReplicationTrack connection attribute or the ALTER SESSION SET REPLICATION_TRACK statement. After which, all transactions for this connection use this track. The transactions for this track are applied in the order in which they are received on the target database, but commit order is not maintained for transactions across the different tracks. If you decide to specify the track for a transaction, then make sure that you distribute the workload evenly across the tracks.

Updates that should be applied in order on the receiving side should use the same track. You can spread operations on a table across separate tracks based on key values. For example, if you have a telecom billing application, you can use hash of the account number to set the track and send all transactions for each account on a separate track.

TimesTen still computes and enforces dependencies to make sure that dependent transactions are applied in the correct order on the receiving side.

The application assigns transactions to tracks by one of these methods:

- Set the ReplicationTrack general connection attribute to a nonzero number. All transactions issued by the connection are assigned to this track. The value can be any number. TimesTen maps the ReplicationTrack number for this connection to one of the available parallel replication threads. Thus, the application can use any number to group transactions that should be applied in order. See "ReplicationTrack" in Oracle TimesTen In-Memory Database Reference.

- Use the ALTER SESSION SQL statement to set the replication track number for the current connection. See "ALTER SESSION" in Oracle TimesTen In-Memory Database SQL Reference.

- Use the TT_REPLICATION_TRACK ODBC connection option for the SQLSetConnectOption ODBC function. See "Features for use with replication" in Oracle TimesTen In-Memory Database C Developer's Guide

- Use the setReplicationTrack() method of the TimesTenConnection JDBC class. See "Features for use with replication" in Oracle TimesTen In-Memory Database Java Developer's Guide

Use the ttConfiguration built-in procedure to return the replication track number for the current connection. Use the ttLogHolds built-in procedure to verify that multiple tracks are being used.

Configuring user-defined parallel replication for classic replication schemes

If your application uses a classic replication scheme, has predictable transactional dependencies, and does not require the commit order on the target database be the same as the order on the source database, then you can increase replication throughput by using user-defined parallel replication to manually divide work across different tracks.

User-defined parallel replication configures multiple threads for sending updates from the source database to the target database and for applying the updates on the target database. The application always assigns transactions to tracks. The application specifies which track a transaction belongs to when the transaction starts on the source database. The transactions in each track are applied in the order in which they are received on the target database, but commit order is not maintained for transactions across the different tracks.

Note:
Use caution in assigning tracks to transactions that affect tables with foreign key relationships. If transactions on related tables are assigned to different tracks, one of the transactions can be lost because the transactions may be applied out of commit order.

In general, transactions that modify the same table should be assigned to the same replication track. In addition, updates that should be applied in order on the receiving side should use the same track. However, if all transactions insert to a particular table, they can be assigned to different tracks to increase replication throughput. You can split the workload for a table across multiple tracks with a key that ties a row to the same track.

User-defined parallel replication is used only for classic replication schemes.

Enable user-defined parallel replication by setting these data store attributes at database creation time:

- Set ReplicationApplyOrdering to 1.

- Set ReplicationParallelism to a number from 1 to 64. This number indicates the number of transmitter threads on the source database and the number of receiver threads on the target database. For single threaded replication, set to 1 (the default). To use parallel replication, set to a number from 2 to 64.

In addition, the application needs to assign transactions to tracks with the same method as described in "Specifying replication tracks within an automatic parallel replication environment". The only difference is that a user-defined parallel replication scheme always specifies the track to use for the transactions of the connection.

Restrictions on user-defined parallel replication

- Do not configure user-defined parallel replication for tables that have an aging policy defined.

- Databases configured for user-defined parallel replication cannot contain cache groups.

- A database cannot be defined as a propagator when user-defined parallel replication is configured.

- User-defined parallel replication is not supported for use within an active standby pair replication scheme.

- User-defined parallel replication is not supported for synchronous replication, including databases with the RETURN RECEIPT and RETURN TWOSAFE attributes.

- Cross-release replication and migration from a database that does not have user-defined parallel replication enabled to a database that does have user-defined parallel replication enabled is not supported from release 11.2.1.6.0 until 11.2.1.8.0. It is supported from releases earlier than 11.2.1.6.0 and from 11.2.1.8.0 and later. Users of releases from 11.2.1.6.0 to 11.2.1.8.0 can perform an upgrade by first applying an in-place patch release upgrade to 11.2.1.8.0. For details, see "Upgrades when using parallel replication" in the Oracle TimesTen In-Memory Database Installation Guide.

Managing the transaction log on a replicated database

This section includes these topics:

- About log buffer flushing

- About transaction log growth on a master database

- Setting connection attributes for logging

About log buffer flushing

A dedicated subdaemon thread writes the contents of the log buffer to disk periodically. These writes may be synchronous or buffered. The subdaemon thread ensures that the system I/O buffer never fills up with more transaction log data than the value of the LogFileSize first connection attribute without being synchronized to the log buffer.

If the database is configured with LogFlushMethod=2, then all writes to the disk are synchronous writes and the data is durably written to disk before the write call returns. If the database is configured with LogFlushMethod=1, then the writes are buffered unless there is a specific request from an application for synchronous writes.

In addition to the periodic writes, an application can also trigger the subdaemon thread to write the buffer contents to disk. The following are cases where the application triggers a synchronous write to the disk:

- When a transaction that requested a durable commit is committed. A transaction can request a durable commit by calling the ttDurableCommit built-in procedure or by having the DurableCommits connection attribute set to 1.

- When the replication agent sends a batch of transactions to a subscriber and the master has been configured for replication with the TRANSMIT DURABLE attribute (the default).

- When the replication agent periodically executes a durable commit, whether the master database is configured with TRANSMIT DURABLE or not.

Transactions are also written to disk durably when durable commits are configured as part of the return service failure policies and a failure has occurred.

The size of the log buffer has no influence on the ability of TimesTen to write data to disk under any of the circumstances listed above.

About transaction log growth on a master database

In databases that do not use replication, Transaction Log API (XLA), cache groups or incremental backup, unneeded records in the log buffer and unneeded transaction log files are purged each time a checkpoint is initiated, either by the automatic background checkpointing thread or by an application's call to the ttCkpt or ttCkptBlocking built-in procedures. In a replicated database, transactions remain in the log buffer and transaction log files until the master replication agent confirms they have been fully processed by the subscriber. Only then can the master consider purging them from the log buffer and transaction log files.

A master database transaction log can grow much larger than it would on an unreplicated database if there are changes to its subscriber state. When the subscriber is in the start state, the master can purge logged data after it receives confirmation that the information has been received by the subscriber. However, if a subscriber becomes unavailable or is in the pause state, the log on the master database cannot be flushed and the space used for logging can be exhausted. When the log space is exhausted, subsequent updates on the master database are aborted. Use the ttLogHolds built-in procedure to get information about replication log holds.

Note:
For more information about transaction log growth, see "Monitoring accumulation of transaction log files" in Oracle TimesTen In-Memory Database Operations Guide. For more details on the ttLogHolds built-in procedure, see "Monitor replication with the ttLogHolds built-in procedure" or "ttLogHolds" in the Oracle TimesTen In-Memory Database Reference.

Setting connection attributes for logging

LogBufMB specifies the maximum size of the in-memory log buffer in megabytes. This buffer is flushed to a transaction log file on the disk when it becomes full. The minimum size for LogBufMB is 8 times the value of LogBufParallelism.

You need to establish enough disk space for the transaction log files. There are two settings that control the amount of disk space used by the log:

- The LogFileSize setting in the DSN specifies the maximum size of a transaction log file. If logging requirements exceed this value, additional transaction log files with the same maximum size are created. For best performance, set LogBufMB and LogFileSize to their maximum values.

- The log failure threshold setting specifies the maximum number of transaction log files allowed to accumulate before the master assumes a subscriber has failed. The threshold value is the number of transaction log files between the most recently written to transaction log file and the earliest transaction log file being held for the subscriber. For example, if the last record successfully received by all subscribers was in Log File 1 and the last log record written to disk is at the beginning of Log File 4, then replication is at least 2 transaction log files behind (the contents of Log Files 2 and 3). If the threshold value is 2, then the master sets the subscriber to the failed state after detecting the threshold value had been exceeded. This may take up to 10 seconds. See "Setting the transaction log failure threshold" for more information.

Because transactions are logged to disk, you can use bookmarks to detect the log record identifiers of the update records that have been replicated to subscribers and those that have been written to disk. To view the location of the bookmarks for the subscribers associated with masterDSN, use the ttBookmark built-in procedure, as described in "Show replicated log records".

If a subscriber goes down and then comes back up before the threshold is reached, then replication automatically "catches up" as the committed transactions in the transaction log files following the bookmark are automatically transmitted. However, if the threshold is exceeded, the master sets the subscriber to the failed state. A failed subscriber must use ttRepAdmin -duplicate to copy the master database and start over, as described in Chapter 15, "Managing Database Failover and Recovery".

See Oracle TimesTen In-Memory Database Reference for more information about TimesTen connection attributes, built-in procedures and utilities.

Duplicating a master database to a subscriber

The simplest method for populating a subscriber database is to duplicate the contents of the master database. Duplicating a database in this manner is also essential when recovering a failed database, as described in Chapter 15, "Managing Database Failover and Recovery". You can use the ttRepAdmin -duplicate utility or the ttRepDuplicateEx C function to duplicate a database.

To duplicate a database, these conditions must be fulfilled:

- The instance administrator performs the duplicate operation.

- The instance administrator user name must be the same on both instances involved in the duplication.

- You must provide the user name and password for a user with the ADMIN privilege on the source database.

- The target DSN cannot include client/server attributes.

To duplicate the contents of a master database to a subscriber database, complete these tasks:

1. Create or alter a replication scheme to include the new subscriber database and its host. See "Defining a classic replication scheme" or "Creating and adding a subscriber database to a classic replication scheme".

2. Apply the replication scheme to the master database. See "Applying a classic replication scheme to a database".

3. Start the replication agent for the master database. See "Starting and stopping the replication agents".

4. On the source database (the master), create a user and grant the ADMIN privilege to the user:

CREATE USER ttuser IDENTIFIED BY ttuser;
User created.

GRANT admin TO ttuser;

5. Assume the user name of the instance administrator is timesten. Logged in as timesten on the target host (the subscriber), duplicate database masterDSN on host1 to subscriber1DSN:

ttRepAdmin -duplicate -from masterDSN -host host1 subscriber1DSN

Enter internal UID at the remote datastore with ADMIN privileges: ttuser
Enter password of the internal Uid at the remote datastore:

Enter ttuser when prompted for the password of the internal user at the remote database.

Note:
The host entry can be identified with either the name of the remote host or its TCP/IP address. If you identify hosts using TCP/IP addresses, you must identify the address of the local host (host1 in this example) by using the -localhost option.
You can specify the local and remote network interfaces for the source and target hosts by using the -localIP and -remoteIP options of ttRepAdmin -duplicate. If you do not specify one or both network interfaces, TimesTen chooses them.

For details, see "ttRepAdmin" in Oracle TimesTen In-Memory Database Reference.

6. Start the replication agent on the subscriber database.

Configuring a large number of subscribers

A replication scheme can include up to 128 subscribers. A replication scheme with propagator databases can have up to 128 propagators, and each propagator can have up to 128 subscribers. An active standby pair replication scheme can include up to 127 read-only subscribers. If you are planning a replication scheme that includes a large number of subscribers, then ensure the following:

- The log buffer size should result in the value of LOG_FS_READS in the SYS.MONITOR table being 0 or close to 0. This ensures that the replication agent does not have to read any log records from disk. If the value of LOG_FS_READS is increasing, then increase the log buffer size.

- CPU resources are adequate. The replication agent on the master database spawns a thread for every subscriber database. Each thread reads and processes the log independently and needs adequate CPU resources to transmit to the subscriber database.

Replicating databases across releases

Replication functions across releases only if the database of the more recent version of TimesTen was upgraded using ttMigrate from a database of the older version of TimesTen. A database created in the current version of TimesTen is not guaranteed to replicate correctly with the older version.

For example, replication between a database created in TimesTen release 6.0 and a database created in TimesTen release 11.2.1 is not supported. However, if one database was created in TimesTen release 6.0, and the peer database was created in TimesTen release 6.0 and then upgraded to TimesTen release 11.2.1, replication between them is supported.

See "TimesTen Upgrades" in Oracle TimesTen In-Memory Database Installation Guide.

Starting and stopping the replication agents

After you have defined a replication scheme, you can start the replication agents for each database involved in the replication scheme. You must have the ADMIN privilege to start or stop a replication agent.

You can start and stop a replication agent by using the ttAdmin utility with the -repStart or -repStop option. You can also use the ttRepStart and ttRepStop built-in procedures to start and stop a replication agent from the ttIsql command line.

Example 11-1 Starting and stopping the replication agent with ttAdmin

To start the replication agents for the DSNs named masterDSN and subscriberDSN, enter:

ttAdmin -repStart masterDSN
ttAdmin -repStart subscriberDSN

To stop the replication agents, enter:

ttAdmin -repStop masterDSN
ttAdmin -repStop subscriberDSN

Example 11-2 Starting and stopping the replication agent from ttIsql

To start and stop the replication agent for the DSN named masterDSN, enter:

> ttIsql masterDSN
Command> call ttRepStart;
Command> call ttRepStop;

You can also use the ttAdmin utility to set the replication restart policy. By default the policy is manual, which enables you to start and stop the replication agents as described above. Alternatively, you can set the replication restart policy for a database to always or norestart.

Restart Policy

Start replication agent when the TimesTen daemon starts

Restart replication agent on errors or invalidation

always

Yes

Yes

manual

No

Yes

norestart

No

No

Note:
The TimesTen daemon manages the replication agents. It must be running to start or stop the replication agents.

When the restart policy is always, the replication agent is automatically started when the database is loaded into memory. See "Specifying a RAM policy" in Oracle TimesTen In-Memory Database Operations Guide to determine when a database is loaded into memory.

Example 11-3 Using ttAdmin to set the restart policy

To use ttAdmin to set the replication restart policy to always, enter:

ttAdmin -repPolicy always DSN

To reset the policy back to manual, enter:

ttAdmin -repPolicy manual DSN

Following a database invalidation, both manual and always policies cause the replication agent to be automatically restarted. When the agent restarts automatically, it is often the first connection to the database. This happens after a fatal error that, for example, requires all applications to disconnect. The first connection to a database usually has to load the most recent checkpoint file and often needs to do recovery. For a very large database, this process may take several minutes. During this period, all activity on the database is blocked so that new connections cannot take place and any old connections cannot finish disconnecting. This may also result in two copies of the database existing at the same time because the old one stays around until all applications have disconnected. For very large databases for which the first-connect time may be significant, you may want to wait for the old database to become inactive first before starting up the new one. You can do this by setting the restart policy to norestart to specify that the replication agent is not to be automatically restarted. For more information on setting policies that would prevent the database from being reloaded, see "Specifying a RAM policy" in Oracle TimesTen In-Memory Database Operations Guide to determine when a database is loaded into memory.

Setting the replication state of subscribers

The state of a subscriber replication agent is described by its master database. When recovering a failed subscriber database, you must reset the replication state of the subscriber database with respect to the master database it communicates with in a replication scheme. You can reset the state of a subscriber database from either the command line or your program:

- From the command line, use ttRepAdmin -state to direct a master database to reset the replication state of one of its subscriber databases.

- From ttIsql, call the ttRepSubscriberStateSet built-in procedure to direct a master database to reset the replication state of one or all of its subscriber databases.

See Chapter 12, "Monitoring Replication" for information about querying the state of a database.

A master database can set a subscriber database to either the start, pause, or stop states. The database state appears as an integer value in the STATE column in the TTREP.REPPEERS table, as shown in Table 11-1.

Table 11-1 Database states

State

Description

start

STATE value: 0

Replication updates are collected and transmitted to the subscriber database as soon as possible. If replication for the subscriber database is not operational, the updates are saved in the transaction log files until they can be sent.

pause

STATE value: 1

Replication updates are retained in the log with no attempt to transmit them. Transmission begins when the state is changed to start.

stop

STATE value: 2

Replication updates are discarded without being sent to the subscriber database. Placing a subscriber database in the stop state discards any pending updates from the master's transaction log.

WARNING: If you are planning on restarting this subscriber, updates are not stored between the stop and the restart. Therefore, when you restart, the subscriber does not contain all of the updates from the master. If you are planning to restart, pause the subscriber instead of stopping it.

failed

STATE value: 4

Replication to a subscriber is considered failed because the threshold limit (log data) has been exceeded. This state is set by the system is a transitional state before the system sets the state to stop. Applications that connect to a failed database receive a warning. See "General failover and recovery procedures" for more information.

When a master database sets one of its subscribers to the start state, updates for the subscriber are retained in the master's log. When a subscriber is in the stop state, updates intended for it are discarded.

When a subscriber is in the pause state, updates for it are retained in the master's log, but are not transmitted to the subscriber database. When a master transitions a subscriber from pause to start, the backlog of updates stored in the master's log is transmitted to the subscriber. (There is an exception to this, which is described in Chapter 15, "Managing Database Failover and Recovery".) If a master database is unable to establish a connection to a stated subscriber, the master periodically attempts to establish a connection until successful.

Example 11-4 Using ttRepAdmin to set the subscriber state

To use ttRepAdmin from the command line to direct the masterds master database to set the state of the subscriberds subscriber database to stop:

ttRepAdmin -dsn masterds -receiver -name subscriberds -state stop

Note:
If you have multiple subscribers with the same name on different hosts, use the -host option of the ttRepAdmin utility to identify the host for the subscriber that you want to modify.

Example 11-5 Using ttRepSubscriberStateSet to set the subscriber state

On the master database, call the ttRepSubscriberStateSet built-in procedure to set the state of the subscriber database (subscriberds ON system1) in the repscheme replication scheme to stop:

Command> CALL ttRepSubscriberStateSet('repscheme', 'repl',
'subscriberds', 'system1', 2);

Only ttRepSubscriberStateSet can be used to set all of the subscribers of a master to a particular state.The ttRepAdmin utility does not have any equivalent functionality.

12 Monitoring Replication

This chapter describes some of the TimesTen utilities and built-in procedures you can use to monitor the replication status of your databases.

You can monitor replication from both the command line and within your programs. The ttStatus and ttRepAdmin utilities described in this chapter are useful for command line queries. To monitor replication from your programs, you can use the TimesTen built-in procedures described in Oracle TimesTen In-Memory Database Reference or create your own SQL SELECT statements to query the replication tables described in Oracle TimesTen In-Memory Database System Tables and Views Reference.

Note:
You can only access the TimesTen SYS and TTREP tables for queries. Do not try to alter the contents of these tables.

This chapter includes the following topics:

- Show state of replication agents

- Show master database information

- Show subscriber database information

- Show the configuration of replicated databases

- Show replicated log records

- Use ttRepAdmin to show replication status

- Check the status of return service transactions

- Analyze outstanding transactions in the replication log

Show state of replication agents

You can display information about the current state of the replication agents:

- Using ttStatus to obtain replication agent status

- Using ttAdmin -query to confirm policy settings

- Using ttDataStoreStatus to obtain replication agent status

You can also obtain the state of specific replicated databases as described in "Show subscriber database information" and "Show the configuration of replicated databases".

Using ttStatus to obtain replication agent status

Use the ttStatus utility to confirm that the replication agent is started for the master database.

Example 12-1 Using ttStatus to obtain replication agent status

> ttStatus
TimesTen status report as of Thu Aug 11 17:05:23 2011
Daemon pid 18373 port 4134 instance ttuser
TimesTen server pid 18381 started on port 4136
------------------------------------------------------------------------
Data store /tmp/masterds
There are 16 connections to the data store
Shared Memory KEY 0x0201ab43 ID 5242889
PL/SQL Memory KEY 0x0301ab43 ID 5275658 Address 0x10000000
Type            PID     Context     Connection Name              ConnID
Process         20564   0x081338c0  masterds                          1
Replication     20676   0x08996738  LOGFORCE                          5
Replication     20676   0x089b69a0  REPHOLD                           2
Replication     20676   0x08a11a58  FAILOVER                          3
Replication     20676   0x08a7cd70  REPLISTENER                       4
Replication     20676   0x08ad7e28  TRANSMITTER                       6
Subdaemon       18379   0x080a11f0  Manager                        2032
Subdaemon       18379   0x080fe258  Rollback                       2033
Subdaemon       18379   0x081cb818  Checkpoint                     2036
Subdaemon       18379   0x081e6940  Log Marker                     2035
Subdaemon       18379   0x08261e70  Deadlock Detector              2038
Subdaemon       18379   0xae100470  AsyncMV                        2040
Subdaemon       18379   0xae11b508  HistGC                         2041
Subdaemon       18379   0xae300470  Aging                          2039
Subdaemon       18379   0xae500470  Flusher                        2034
Subdaemon       18379   0xae55b738  Monitor                        2037
Replication policy  : Manual
Replication agent is running.
Cache Agent policy  : Manual
PL/SQL enabled.

Using ttAdmin -query to confirm policy settings

Use the ttAdmin utility with the -query option to confirm the policy settings for a database, including the replication restart policy described in "Starting and stopping the replication agents".

Example 12-2 Using ttAdmin to confirm policy settings

> ttAdmin -query masterDSN
RAM Residence Policy : inUse
Manually Loaded In Ram : False
Replication Agent Policy : manual
Replication Manually Started : True
Cache Agent Policy : manual
Cache Agent Manually Started : False

Using ttDataStoreStatus to obtain replication agent status

To obtain the status of the replication agents from a program, use the ttDataStoreStatus built-in procedure.

Example 12-3 Calling ttDataStoreStatus

Call the ttDataStoreStatus built-in procedure to obtain the status of the replication agents for the masterds databases:

> ttIsql masterds
Command> CALL ttDataStoreStatus('/tmp/masterds');
< /tmp/masterds, 964, 00000000005D8150, subdaemon, Global\DBI3b3234c0.0.SHM.35 >
< /tmp/masterds, 1712, 00000000016A72E0, replication, Global\DBI3b3234c0.0.SHM.35 >
< /tmp/masterds, 1712, 0000000001683DE8, replication, Global\DBI3b3234c0.0.SHM.35 >
< /tmp/masterds, 1620, 0000000000608128, application, Global\DBI3b3234c0.0.SHM.35 >
4 rows found.

The output from ttDataStoreStatus is similar to that shown for the ttStatus utility in "Using ttStatus to obtain replication agent status".

Show master database information

You can display information for a master database:

- Using ttRepAdmin to display information about the master database

- Querying replication tables to obtain information about a master database

Using ttRepAdmin to display information about the master database

Use the ttRepAdmin utility with the -self -list options to display information about the master database:

ttRepAdmin -dsn masterDSN -self -list

Example 12-4 Using ttRepAdmin to display information about a master database

This example shows the output for the master database described in "Multiple subscriber classic replication schemes with return services and a log failure threshold".

> ttRepAdmin -dsn masterds -self -list
Self host "server1", port auto, name "masterds", LSN 0/2114272

The following table describes the fields.

Field

Description

host

The name of the host for the database.

port

TCP/IP port used by a replication agent of another database to receive updates from this database. A value of 0 (zero) indicates replication has automatically assigned the port.

name

Name of the database.

Log file/Replication hold LSN

Indicates the oldest location in the transaction log that is held for possible transmission to the subscriber. A value of -1/-1 indicates replication is in the stop state with respect to all subscribers.

Querying replication tables to obtain information about a master database

Use the following SELECT statement to query the TTREP.TTSTORES and TTREP.REPSTORES replication tables to obtain information about a master database:

SELECT t.host_name, t.rep_port_number, t.tt_store_name
FROM ttrep.ttstores t, ttrep.repstores s
WHERE t.is_local_store = 0x01
AND t.tt_store_id = s.tt_store_id;

This is the output of the SELECT statement for the master database described in "Multiple subscriber classic replication schemes with return services and a log failure threshold". The fields are the host name, the replication port number, and the database name.

< server1, 0, masterds>

Show subscriber database information

Replication uses the TimesTen transaction log to retain information that must be transmitted to subscriber sites. When communication to subscriber databases is interrupted or the subscriber sites are down, the transaction log data accumulates. Part of the output from the queries described in this section enables you to see how much transaction log data has accumulated on behalf of each subscriber database and the amount of time since the last successful communication with each subscriber database.

Use the following methods to display information for subscriber databases:

- Display subscriber status with the ttRepAdmin utility

- Display subscriber status with the ttReplicationStatus built-in procedure

- Display information about subscribers through querying replication tables

Display subscriber status with the ttRepAdmin utility

To display information about subscribers, use the ttRepAdmin utility with the -receiver -list options:

ttRepAdmin -dsn masterDSN -receiver -list

Example 12-5 Using ttRepAdmin to display information about subscribers

This example shows the output for the subscribers described in "Multiple subscriber classic replication schemes with return services and a log failure threshold".

> ttRepAdmin -dsn masterds -receiver -list
Peer name        Host name                Port   State   Proto
---------------- ------------------------ ------ ------- -----
subscriber1ds    server2                  Auto   Start      10

Last Msg Sent Last Msg Recv Latency TPS     RecordsPS Logs
------------- ------------- ------- ------- --------- ----
0:01:12       -             19.41 5       5        52    2

Peer name        Host name                Port   State   Proto
---------------- ------------------------ ------ ------- -----
subscriber2ds    server3                  Auto   Start      10

Last Msg Sent Last Msg Recv Latency TPS     RecordsPS Logs
------------- ------------- ------- ------- --------- ----
0:01:04       -             20.94         4        48    2

The first line of the display contains the subscriber definition. The following row of the display contains latency and rate information, as well as the number of transaction log files being retained on behalf of this subscriber. The latency for subscriber1ds is 19.41 seconds, and it is 2 logs behind the master. This is a high latency, indicating a problem if it continues to be high and the number of logs continues to increase.

Note:
See "Subscriber information" for details on the subscriber information displayed.

If you have more than one scheme specified in the TTREP.REPLICATIONS table, you must use the -scheme option to specify which scheme you want to list. Otherwise you receive the following error:

Must specify -scheme to identify which replication scheme to use

For more information, see "ttRepAdmin" in the Oracle TimesTen In-Memory Database Reference.

Display subscriber status with the ttReplicationStatus built-in procedure

Within ttIsql, you can display status for a one or more subscriber databases by using the ttReplicationStatus built-in procedure, which reports only on the status of the subscribers for the master database on which this built-in procedure is called.

Example 12-6 Display status of a single subscriber of this master

The following retrieves status for the subscriber master2 that is located on host1. If the host name is excluded, the subscriber is located solely on its name.

Command> call ttReplicationStatus('master2', 'host1');
< MASTER2, HOST1, 0, start, 1, 26, _ACTIVESTANDBY , TTREP >
1 row found.

The information shown is that the subscriber master2 located on host1 that is listening on an automatically assigned port. The TCP/IP port is used by the subscriber agent to receive updates from the master. However, since the value is zero, this indicates replication has automatically assigned the port.

This subscriber is in the start state. There is only one transaction log being held for this peer and 26 seconds have passed since the last replication. The name of the replication scheme is _ACTIVESTANDBY and the owner is TTREP.

Example 12-7 Display status for all subscribers of this master

If you do not provide either a subscriber or the subscriber host names, then the status for all subscribers of this master are returned. The following shows the same status as above, since there is only one subscriber set up for this master.

Command> call ttReplicationStatus();
< MASTER2, HOST1, 0, start, 1, 26, _ACTIVESTANDBY , TTREP >
1 row found.

For more information, see "ttReplicationStatus" in the Oracle TimesTen In-Memory Database Reference.

Display information about subscribers through querying replication tables

You can obtain the same information about a master's subscribers from a program by querying the TTREP.REPPEERS, TTREP.TTSTORES, and SYS.MONITOR tables with the following SELECT statement:

SELECT t1.tt_store_name, t1.host_name, t1.rep_port_number,
p.state, p.protocol, p.timesend, p.timerecv, p.latency,
p.tps, p.recspersec, t3.last_log_file - p.sendlsnhigh + 1
FROM ttrep.reppeers p, ttrep.ttstores t1, ttrep.ttstores t2, sys.monitor t3
WHERE p.tt_store_id = t1.tt_store_id
AND t2.is_local_store = 0X01
AND p.subscriber_id = t2.tt_store_id
AND p.replication_name = 'repscheme'
AND p.replication_owner = 'repl'
AND (p.state = 0 OR p.state = 1);

The following is sample output from the 3 statement above:

< subscriber1ds, server2, 0, 0, 7, 1003941635, 0, -1.00000000000000, -1, -1, 1 >
< subscriber2ds, server3, 0, 0, 7, 1003941635, 0, -1.00000000000000, -1, -1, 1 >

See "Subscriber information" for details on the subscriber information displayed.

Subscriber information

The output from either the ttRepAdmin utility or the SELECT statement contains the following fields:

Field

Description

Peer name

Name of the subscriber database

Host name

Name of the machine that hosts the subscriber

Port

TCP/IP port used by the subscriber agent to receive updates from the master. A value of 0 indicates replication has automatically assigned the port.

State

Current replication state of the subscriber with respect to its master database (see "Show subscriber database information" for information).

Protocol

Internal protocol used by replication to communicate between this master and its subscribers. You can ignore this value.

Last message sent

Time (in seconds) since the master sent the last message to the subscriber. This includes the "heartbeat" messages sent between the databases.

Last message received

Time (in seconds) since this subscriber received the last message from the master.

Latency

The average latency time (in seconds) between when the master sends a message and when it receives the final acknowledgement from the subscriber. (See note below.)

Transactions per second

The average number of transactions per second that are committed on the master and processed by the subscriber. (See note below.)

Records per second

The average number of transmitted records per second. (See note below.)

Logs

Number of transaction log files the master database is retaining for a subscriber.

Note:
Latency, TPS, and RecordsPS report averages detected while replicating a batch of records. These values can be unstable if the workload is not relatively constant. A value of -1 indicates the master's replication agent has not yet established communication with its subscriber replication agents or sent data to them.

Show the configuration of replicated databases

You can display the configuration of your replicated databases:

- Display configuration information with the ttIsql repschemes command

- Display configuration information with the ttRepAdmin utility

- Display configuration information through querying replication tables

Display configuration information with the ttIsql repschemes command

To display the configuration of your replicated databases from the ttIsql prompt, use the repschemes command:

Command> repschemes;

Example 12-8 shows the configuration output from the replication scheme shown in "Propagation scheme".

Example 12-8 Output from ttIsql repschemes command

Replication Scheme PROPAGATOR:

Element: A
Type: Table TAB
Master Store: CENTRALDS on FINANCE Transmit Durable
Subscriber Store: PROPDS on NETHANDLER

Element: B
Type: Table TAB
Propagator Store: PROPDS on NETHANDLER Transmit Durable
Subscriber Store: BACKUP1DS on BACKUPSYSTEM1
Subscriber Store: BACKUP2DS on BACKUPSYSTEM2

Store: BACKUP1DS on BACKUPSYSTEM1
Port: (auto)
Log Fail Threshold: (none)
Retry Timeout: 120 seconds
Compress Traffic: Disabled

Store: BACKUP2DS on BACKUPSYSTEM2
Port: (auto)
Log Fail Threshold: (none)
Retry Timeout: 120 seconds
Compress Traffic: Disabled

Store: CENTRALDS on FINANCE
Port: (auto)
Log Fail Threshold: (none)
Retry Timeout: 120 seconds
Compress Traffic: Disabled

Store: PROPDS on NETHANDLER
Port: (auto)
Log Fail Threshold: (none)
Retry Timeout: 120 seconds
Compress Traffic: Disabled

Display configuration information with the ttRepAdmin utility

To display the configuration of your replicated databases, use the ttRepAdmin utility with the -showconfig option:

ttRepAdmin -showconfig -dsn masterDSN

Example 12-9 shows the configuration output from the propagated databases configured by the replication scheme shown in "Propagation scheme". The propds propagator shows a latency of 19.41 seconds and is 2 logs behind the master.

Example 12-9 ttRepAdmin output

> ttRepAdmin -showconfig -dsn centralds
Self host "finance", port auto, name "centralds", LSN 0/155656, timeout 120,
threshold 0

List of subscribers
-----------------
Peer name        Host name                Port   State   Proto
---------------- ------------------------ ------ ------- -----
propds           nethandler               Auto   Start      10

Last Msg Sent Last Msg Recv Latency TPS     RecordsPS Logs
------------- ------------- ------- ------- --------- ----
0:01:12       -             19.41         5        52    2

List of tables and subscriptions
--------------------------------
Table details
-------------
Table : tab          Timestamp updates : -

Master Name                 Subscriber Name
-----------                 -------------
centralds                   propds

Table details
-------------
Table : tab          Timestamp updates : -

Master Name                 Subscriber name
-----------                 -------------
propds                      backup1ds
propds                      backup2ds

See "Display information about subscribers through querying replication tables" for the meaning of the "List of subscribers" fields. The "Table details" fields list the table and the names of its master (Sender) and subscriber databases.

Display configuration information through querying replication tables

Use the following SELECT statements to query the TTREP.TTSTORES, TTREP.REPSTORES, TTREP.REPPEERS, SYS.MONITOR, TTREP.REPELEMENTS, and TTREP.REPSUBSCRIPTIONS tables for configuration information:

SELECT t.host_name, t.rep_port_number, t.tt_store_name, s.peer_timeout,
s.fail_threshold
FROM ttrep.ttstores t, ttrep.repstores s
WHERE t.is_local_store = 0X01
AND t.tt_store_id = s.tt_store_id;

SELECT t1.tt_store_name, t1.host_name, t1.rep_port_number,
p.state, p.protocol, p.timesend, p.timerecv, p.latency,
p.tps, p.recspersec, t3.last_log_file - p.sendlsnhigh + 1
FROM ttrep.reppeers p, ttrep.ttstores t1, ttrep.ttstores t2, sys.monitor t3
WHERE p.tt_store_id = t2.tt_store_id
AND t2.is_local_store = 0X01
AND p.subscriber_id = t1.tt_store_id
AND (p.state = 0 OR p.states = 1);

SELECT ds_obj_owner, DS_OBJ_NAME, t1.tt_store_name,t2.tt_store_name
FROM ttrep.repelements e, ttrep.repsubscriptions s,
ttrep.ttstores t1, ttrep.ttstores t2
WHERE s.element_name = e.element_name
AND e.master_id = t1.tt_store_id
AND s.subscriber_id = t2.tt_store_id
ORDER BY ds_obj_owner, ds_obj_name;

Example 12-10 Output from queries

The output from the queries refer to the databases configured by the replication scheme shown in "Propagation scheme".

The output from the first query might be:

< finance, 0, centralds, 120, 0 >

It shows the host name, port number and the database name. The fourth value (120) is the TIMEOUT value that defines the amount of time a database waits for a response from another database before resending a message. The last value (0) is the log failure threshold value described in "Setting the transaction log failure threshold".

The output from the second query might be:

< propds, nethandler, 0, 0, 7, 1004378953, 0, -1.00000000000000, -1, -1, 1 >

See "Display information about subscribers through querying replication tables" for a description of the fields.

The output from the last query might be:

< repl, tab, centralds, propds >
< repl, tab, propds, backup1ds >
< repl, tab, propds, backup2ds >

The rows show the replicated table and the names of its master (sender) and subscriber (receiver) databases.

Show replicated log records

In a replicated database, transactions remain in the transaction log buffer and transaction log files until the master replication agent confirms they have been fully processed by the subscriber. In an active standby pair replication scheme that contains subscribers, transactions remain in the transaction logs until the active master confirms that they are processed by both the standby master and any subscribers. Only then can the active master consider purging them from the log buffer and transaction log files. When the log space is exhausted, subsequent updates on the master database are aborted.

Note:
For more information about transaction log growth, see "Monitoring accumulation of transaction log files" in Oracle TimesTen In-Memory Database Operations Guide.

Transactions are stored in the log in the form of log records. You can use bookmarks to detect which log records have or have not been replicated by a master database. A bookmark consists of log sequence numbers (LSNs) that identify the location of particular records in the transaction log that you can use to gauge replication performance. The LSNs associated with a bookmark are: hold LSN, last written LSN, and last LSN forced to disk. The hold LSN describes the location of the lowest (or oldest) record held in the log for possible transmission to a subscriber. You can compare the hold LSN with the last written LSN to determine the amount of data in the transaction log that have not yet been transmitted to the subscribers. The last LSN forced to disk describes the last records saved in a transaction log file on disk.

You can monitor replication through bookmarks and the log sequence numbers with the following tools:

- Monitor replication with the TTREP.REPPEERS table

- Monitor replication with the ttLogHolds built-in procedure

- Monitor replication with the ttRepAdmin utility

- Monitor replication with the ttBookMark built-in procedure

Monitor replication with the TTREP.REPPEERS table

An accurate way to monitor replication to a particular subscriber is to look at the send LSN for the subscriber, which consists of the SENDLSNHIGH and SENDLSNLOW fields in the TTREP.REPPEERS table. In contrast to the send LSN value, the hold LSN returned in a bookmark is computed every 10 seconds to describe the minimum send LSN for all the subscribers, so it provides a more general view of replication progress that does not account for the progress of replication to the individual subscribers. Because replication acknowledgements are asynchronous for better performance, the send LSN can also be some distance behind. Nonetheless, the send LSN for a subscriber is the most accurate value available and is always ahead of the hold LSN.

Monitor replication with the ttLogHolds built-in procedure

Use the ttLogHolds built-in procedure to get information about replication log holds.

The following example shows the output of ttLogHolds built-in procedure for an active standby pair replication scheme, where the active master is master1 and the standby master is master2, with a single subscriber, subscriber1. All transactions are replicated from the active master first to the standby master who then propagates the transactions to the subscriber. Thus, the subscriber's progress is slightly behind the standby master's progress.

The active master monitors the progress of both the standby master and the subscriber; therefore, if the standby master goes down for any reason, the active master can take over the replication to the subscriber. The active master receives acknowledgements when transactions are applied on the subscriber so the active master knows when it can release pertinent log records that might be needed if the standby master fails (upon which the active master switches to replicate directly to the subscribers). The transactions remain in the transaction logs until they are processed on both the standby master and the subscriber.

Command> call ttLogHolds;
< 0, 3569664, Checkpoint                    , master1.ds0 >
< 0, 15742976, Checkpoint                    , master1.ds1 >
< 0, 16351496, Replication                   , ADC6160529:SUBSCRIBER1 >
< 0, 16351640, Replication                   , ADC6160529:MASTER2 >
4 rows found.

If you are using an AWT cache group, it uses the replication agent to asynchronously propagate transactions to the Oracle database. When you call the ttLogHolds built-in procedure, the description field contains "_ORACLE" to identify the transaction log hold for the AWT cache group propagation.

Command> call ttLogHolds();
< 0, 18958336, Checkpoint                    , cachealone1.ds0 >
< 0, 19048448, Checkpoint                    , cachealone1.ds1 >
< 0, 19050904, Replication                   , ADC6160529:_ORACLE >
3 rows found.

For more details on the ttLogHolds built-in procedure, see "ttLogHolds" in the Oracle TimesTen In-Memory Database Reference.

Monitor replication with the ttRepAdmin utility

Use the ttRepAdmin utility with the -bookmark option to display the location of bookmarks:

> ttRepAdmin -dsn masterds -bookmark
Replication hold LSN ...... 10/927692
Last written LSN .......... 10/928908
Last LSN forced to disk ... 10/280540
Each LSN is defined by two values:
Log file number / Offset in log file

The LSNs output from ttRepAdmin -bookmark are:

Line

Description

Replication hold LSN

The location of the lowest (or oldest) record held in the log for possible transmission to a subscriber. A value of -1/-1 indicates replication is in the stop state with respect to all subscribers (or the queried database is not a master database).
If you are monitoring an active standby pair with one or more subscribers, then this value denotes the oldest record held for all nodes involved in the replication scheme. For example, in an active standby pair with subscribers, the oldest record could be held in the log for the standby master or any of the subscribers.

Last written LSN

The location of the most recently generated transaction log record for the database.

Last LSN forced to disk

The location of the most recent transaction log record written to the disk.

Monitor replication with the ttBookMark built-in procedure

Use the ttBookmark built-in procedure to display the location of bookmarks.

Example 12-11 Using ttBookmark to display bookmark location

> ttIsql masterds

Command> call ttBookMark();
< 10, 928908, 10, 280540, 10, 927692 >
1 row found.

The first two columns in the returned row define the "Last written LSN," the next two columns define the "Last LSN forced to disk," and the last two columns define the "Replication hold LSN."

If you are monitoring an active standby pair with one or more subscribers, then the "Replication hold LSN" denotes the oldest record held for all nodes involved in the replication scheme. For example, in an active standby pair with subscribers, the oldest record could be held in the log for the standby master or any of the subscribers.

Use ttRepAdmin to show replication status

You can use the ttRepAdmin utility with the -showstatus option to display the current status of the replication agent. The status output includes the bookmark locations, port numbers, and communication protocols used by the replication agent for the queried database.

The output from ttRepAdmin -showstatus includes the status of the main thread and the TRANSMITTER and RECEIVER threads used by the replication agent. A master database has a TRANSMITTER thread and a subscriber database has a RECEIVER thread. A database that serves a master/subscriber role in a bidirectional replication scheme has both a TRANSMITTER and a RECEIVER thread.

Each replication agent has a single REPLISTENER thread that listens on a port for peer connections. On a master database, the REPLISTENER thread starts a separate TRANSMITTER thread for each subscriber database. On a subscriber database, the REPLISTENER thread starts a separate RECEIVER thread for each connection from a master.

If the TimesTen daemon requests that the replication agent stop or if a fatal error occurs in any of the other threads used by the replication agent, the main thread waits for the other threads to gracefully terminate. The TimesTen daemon may or may not restart the replication agent, depending upon certain fatal errors. The REPLISTENER thread never terminates during the lifetime of the replication agent. A TRANSMITTER or RECEIVER thread may stop but the replication agent may restart it. The RECEIVER thread terminates on errors from which it cannot recover or when the master disconnects.

Example 12-11 shows ttRepAdmin -showstatus output for a unidirectional replication scheme in which the rep1 database is the master and rep2 database is the subscriber. The first ttRepAdmin -showstatus output shows the status of the rep1 database and its TRANSMITTER thread. The second output shows the status of the rep2 database and its RECEIVER thread.

Following the example are sections that describe the meaning of each field in the ttRepAdmin -showstatus output:

- MAIN thread status fields

- Replication peer status fields

- TRANSMITTER thread status fields

- RECEIVER thread status fields

Example 12-12 Unidirectional replication scheme

Consider the unidirectional replication scheme from the rep1 database to the rep2 database:

CREATE REPLICATION r
ELEMENT e1 TABLE t
MASTER rep1
SUBSCRIBER rep2;

The replication status for the rep1 database should look similar to the following:

> ttRepAdmin -showstatus rep1

DSN                      : rep1
Process ID               : 1980
Replication Agent Policy : MANUAL
Host                     : MYHOST
RepListener Port         : 1113 (AUTO)
Last write LSN           : 0.1487928
Last LSN forced to disk  : 0.1487928
Replication hold LSN     : 0.1486640

Replication Peers:
Name                   : rep2
Host                   : MYHOST
Port                   : 1154 (AUTO)
Replication State      : STARTED
Communication Protocol : 12

TRANSMITTER thread(s):
For                     : rep2
Start/Restart count   : 2
Send LSN              : 0.1485960
Transactions sent     : 3
Total packets sent    : 10
Tick packets sent     : 3
MIN sent packet size  : 48
MAX sent packet size  : 460
AVG sent packet size  : 167
Last packet sent at   : 17:41:05
Total Packets received: 9
MIN rcvd packet size  : 48
MAX rcvd packet size  : 68
AVG rcvd packet size  : 59
Last packet rcvd'd at : 17:41:05
Earlier errors (max 5):
TT16060 in transmitter.c (line 3590) at 17:40:41 on 08-25-2004
TT16122 in transmitter.c (line 2424) at 17:40:41 on 08-25-2004

Note that the Replication hold LSN, the Last write LSN and the Last LSN forced to disk are very close, which indicates that replication is operating satisfactorily. If the Replication hold LSN falls behind the Last write LSN and the Last LSN, then replication is not keeping up with updates to the master.

The replication status for the rep2 database should look similar to the following:

> ttRepAdmin -showstatus rep2

DSN                      : rep2
Process ID               : 2192
Replication Agent Policy : MANUAL
Host                     : MYHOST
RepListener Port         : 1154 (AUTO)
Last write LSN           : 0.416464
Last LSN forced to disk  : 0.416464
Replication hold LSN     : -1.-1

Replication Peers:
Name              : rep1
Host              : MYHOST
Port              : 0 (AUTO)
Replication State : STARTED
Communication Protocol : 12

RECEIVER thread(s):
For                   : rep1
Start/Restart count   : 1
Transactions received : 0
Total packets sent    : 20
Tick packets sent     : 0
MIN sent packet size  : 48
MAX sent packet size  : 68
AVG sent packet size  : 66
Last packet sent at   : 17:49:51
Total Packets received: 20
MIN rcvd packet size  : 48
MAX rcvd packet size  : 125
AVG rcvd packet size  : 52
Last packet rcvd'd at : 17:49:51

MAIN thread status fields

The following fields are output for the MAIN thread in the replication agent for the queried database.

MAIN Thread

Description

DSN

Name of the database to be queried.

Process ID

Process Id of the replication agent.

Replication Agent Policy

The restart policy, as described in "Starting and stopping the replication agents"

Host

Name of the machine that hosts this database.

RepListener Port

TCP/IP port used by the replication agent to listen for connections from the TRANSMITTER threads of remote replication agents. A value of 0 indicates that this port has been assigned automatically to the replication agent (the default), rather than being specified as part of a replication scheme.

Last write LSN

The location of the most recently generated transaction log record for the database. See "Show replicated log records" for more information.

Last LSN forced to disk

The location of the most recent transaction log record written to the disk. See "Show replicated log records" for more information.

Replication hold LSN

The location of the lowest (or oldest) record held in the log for possible transmission to a subscriber. A value of -1/-1 indicates replication is in the stop state with respect to all subscribers. See "Show replicated log records" for more information.

Replication peer status fields

The following fields are output for each replication peer that participates in the replication scheme with the queried database. A "peer" could play the role of master, subscriber, propagator or both master and subscriber in a bidirectional replication scheme.

Replication Peers

Description

Name

Name of a database that is a replication peer to this database.

Host

Host of the peer database.

Port

TCP/IP port used by the replication agent for the peer database. A value of 0 indicates this port has been assigned automatically to the replication agent (the default), rather than being specified as part of a replication scheme.

Replication State

Current replication state of the replication peer with respect to the queried database (see "Show subscriber database information" for information).

Communication Protocol

Internal protocol used by replication to communicate between the peers. (For internal use only.)

TRANSMITTER thread status fields

The following fields are output for each TRANSMITTER thread used by a master replication agent to send transaction updates to a subscriber. A master with multiple subscribers has multiple TRANSMITTER threads.

Note:
The counts in the TRANSMITTER output begin to accumulate when the replication agent is started. These counters are reset to 0 only when the replication agent is started or restarted.

TRANSMITTER Thread

Description

For

Name of the subscriber database that is receiving replicated data from this database.

Start/Restart count

Number of times this TRANSMITTER thread was started or restarted by the replication agent due to a temporary error, such as operation timeout, network failure, and so on.

Send LSN

The last LSN transmitted to this peer. See "Show replicated log records" for more information.

Transactions sent

Total number of transactions sent to the subscriber.

Total packets sent

Total number of packets sent to the subscriber (including tick packets).

Tick packets sent

Total number of tick packets sent. Tick packets are used to maintain a "heartbeat" between the master and subscriber. You can use this value to determine how many of the 'Total packets sent' packets are not related to replicated data.

MIN sent packet size

Size of the smallest packet sent to the subscriber.

MAX sent packet size

Size of the largest packet sent to the subscriber.

AVG sent packet size

Average size of the packets sent to the subscriber.

Last packet sent at

Time of day last packet was sent (24-hour clock time).

Total packets received

Total packets received from the subscriber (tick packets and acknowledgement data).

MIN rcvd packet size

Size of the smallest packet received.

MAX rcvd packet size

Size of the largest packet received.

AVG rcvd packet size

Average size of the packets received.

Last packet rcvd at

Time of day last packet was received (24-hour clock time).

Earlier errors (max 5)

Last five errors generated by this thread.

RECEIVER thread status fields

The following fields are output for each RECEIVER thread used by a subscriber replication agent to receive transaction updates from a master. A subscriber that is updated by multiple masters has multiple RECEIVER threads.

Note:
The counts in the RECEIVER output begin to accumulate when the replication agent is started. These counters are reset to 0 only when the replication agent is started or restarted.

RECEIVER Thread

Description

For

Name of the master database that is sending replicated data from this database.

Start/Restart count

Number of times this RECEIVER thread was started or restarted by the replication agent due to a temporary error, such as operation timeout, network failure, and so on.

Transactions received

Total number of transactions received from the master.

Total packets sent

Total number of packets sent to the master (tick packets and acknowledgement data).

Tick packets sent

Total number of tick packets sent to the master. Tick packets are used to maintain a "heartbeat" between the master and subscriber. You can use this value to determine how many of the 'Total packets sent' packets are not related to acknowledgement data.

MIN sent packet size

Size of the smallest packet sent to the master.

MAX sent packet size

Size of the largest packet sent to the master.

AVG sent packet size

Average size of the packets sent to the master.

Last packet sent at

Time of day last packet was sent to the master (24-hour clock time).

Total packets received

Total packets of acknowledgement data received from the master.

MIN rcvd packet size

Size of the smallest packet received.

MAX rcvd packet size

Size of the largest packet received.

AVG rcvd packet size

Average size of the packets received.

Last packet rcvd at

Time of day last packet was received (24-hour clock time).

Check the status of return service transactions

The following sections describe how to determine status of a return service or to find out what the last returned status was:

- Determine if return service is disabled

- Check last returned status for a return service

Determine if return service is disabled

You can determine whether the return service for a particular subscriber has been disabled by the DISABLE RETURN failure policy by calling the ttRepSyncSubscriberStatus built-in procedure or by means of the SNMP trap, ttRepReturnTransitionTrap. The ttRepSyncSubscriberStatus built-in procedure returns a value of '1' to indicate the return service has been disabled for the subscriber, or a value of '0' to indicate that the return service is still enabled.

Example 12-13 Using ttRepSyncSubscriberStatus to obtain return receipt status

To use ttRepSyncSubscriberStatus to obtain the return receipt status of the subscriberds database with respect to its master database, masterDSN, enter:

> ttIsql masterDSN

Command> CALL ttRepSyncSubscriberStatus ('subscriberds');
< 0 >
1 row found.

This result indicates that the return service is still enabled.

For information on how to enable or disable the return service, see "Managing return service timeout errors and replication state changes".

Check last returned status for a return service

You can check the status of the last return receipt or return twosafe transaction executed on the connection handle by calling the ttRepXactTokenGet and ttRepXactStatus built-in procedures.

First, call the ttRepXactTokenGet built-in procedure to get a unique token for the last return service transaction. If you are using return receipt, the token identifies the last return receipt transaction committed on the master database. If you are using return twosafe, the token identifies the last twosafe transaction on the master that, in the event of a successful commit on the subscriber, is committed by the replication agent on the master. However, in the event of a timeout or other error, the twosafe transaction identified by the token is not committed by the replication agent on the master.

Next, pass the token returned by ttRepXactTokenGet to the ttRepXactStatus built-in procedure to obtain the return service status. The output of the ttRepXactStatus built-in procedure reports which subscriber or subscribers are configured to receive the replicated data and the current status of the transaction (not sent, received, committed) with respect to each subscriber. If the subscriber replication agent encountered a problem applying the transaction to the subscriber database, the ttRepXactStatus built-in procedure also includes the error string. If you are using return twosafe and receive a timeout or other error, you can then decide whether to unconditionally commit or retry the commit. This is described in "Using a return service".

Note:
If ttRepXactStatus is called without a token from ttRepXactTokenGet, it returns the status of the most recent transaction on the connection which was committed with the return receipt or return twosafe replication service.

The ttRepXactStatus built-in procedure returns the return service status for each subscriber as a set of rows formatted as:

subscriberName, status, error

Example 12-14 Reporting the status of each subscriber

You can call the ttRepXactTokenGet and ttRepXactStatus built-in procedures in a GetRSXactStatus function to report the status of each subscriber in your replicated system:

SQLRETURN GetRSXactStatus (HDBC hdbc)
{
SQLRETURN rc = SQL_SUCCESS;
HSTMT hstmt = SQL_NULL_HSTMT;
char xactId [4001] = "";
char subscriber [62] = "";
char state [3] = "";

/* get the last RS xact id executed on this connection */
SQLAllocStmt (hdbc, &hstmt);
SQLExecDirect (hstmt, "CALL ttRepXactTokenGet ('R2')", SQL_NTS);

/* bind the xact id result as a null terminated hex string */
SQLBindCol (hstmt, 1, SQL_C_CHAR, (SQLPOINTER) xactId,
sizeof (xactId), NULL);

/* fetch the first and only row */
rc = SQLFetch (hstmt);

/* close the cursor */
SQLFreeStmt (hstmt, SQL_CLOSE);

if (rc != SQL_ERROR && rc != SQL_NO_DATA_FOUND)
{
/* display the xact id */
printf ("\nRS Xact ID: 0x%s\n\n", xactId);

/* get the status of this xact id for every subscriber */
SQLBindParameter (hstmt, 1, SQL_PARAM_INPUT, SQL_C_CHAR,
SQL_VARBINARY, 0, 0,
(SQLPOINTER) xactId, strlen (xactId), NULL);

/* execute */
SQLExecDirect (hstmt, "CALL ttRepXactStatus (?)", SQL_NTS);

/* bind the result columns */
SQLBindCol (hstmt, 1, SQL_C_CHAR, (SQLPOINTER) subscriber,
sizeof (subscriber), NULL);

SQLBindCol (hstmt, 2, SQL_C_CHAR, (SQLPOINTER) state,
sizeof (state), NULL);

/* fetch the first row */
rc = SQLFetch (hstmt);

while (rc != SQL_ERROR && rc != SQL_NO_DATA_FOUND)
{
/* report the status of this subscriber */
printf ("\n\nSubscriber: %s", subscriber);
printf ("\nState: %s", state);

/* are there more rows to fetch? */
rc = SQLFetch (hstmt);
}
}

/* close the statement */
SQLFreeStmt (hstmt, SQL_DROP);

return rc;
}

Analyze outstanding transactions in the replication log

You can use the -logAnalyze command in the ttXactLog utility to analyze the replication logs and determine the following:

- Measure how much is left to replicate from a master to any subscribers at the current time. When replication seems to be taking longer than expected, you can determine how many transactions are left to replicate or if replication is processing a long-running transaction.

- Measure if the current configuration distributes the load appropriately across all manual and automatic tracks for parallel replication.

Execute the log analyze command against a particular data store to generate the following information:

- The number of transactions that are waiting to be replicated. For each transaction that has not been replicated, the information collected includes the number of operations for each transaction and the total size of each transaction (including partial rollbacks).

- The amount of operations left in each transaction including its specific type (either DDL or DML) and how many of each statement type are in each transaction. The tool also generates the total size of every operation left to replicate.

- Retrieves information on how the workload is split across tracks. When you use manual parallel replication, you can use -logAnalyze to monitor whether the application is distributing work evenly across the replication tracks.

- Returns the largest transaction left to replicate.

- Returns the start and end LSN. The start LSN is the starting point in the transaction log where the transmitter starts reading; the end LSN is the end of the transaction log.

Note:
In the transaction log analysis output, transactions are shown in commit order.

You can specify how much information is displayed with the verbose command. For example, when you set verbose to 1, the following is displayed:

$ ttXactLog -v1 -logAnalyze rep1
Summary:
Total transactions left to replicate: 4
Total rows left to replicate: 4
Size of transactions left to replicate: 1.86 KiB
Size of rows left to replicate: 488.00 B
Total inserts remaining: 4
Total partial rollbacks: 5
Total rollbacks: 3

Start LSN = 0.3793736
End LSN = 0.18769920

If a subscriber is specified, then the summary displays only for that particular subscriber. However, by default, the summary is displayed for all subscribers.

When you specify verbose to 2, then the information includes both a summary of each parallel track in addition to the overall summary information.

$ ttXactLog -v2 -logAnalyze rep1

Track analysis for track number: 0
Transactions left to replicate: 2
Rows left to replicate: 2
Size of transactions left to replicate: 880.00 B
Size of rows left to replicate: 312.00 B
Total inserts remaining: 1
Total partial rollbacks: 4

Track analysis for track number: 1
Transactions left to replicate: 2
Rows left to replicate: 2
Size of transactions left to replicate: 1.14 KiB
Size of rows left to replicate: 244.00 B
Total inserts remaining: 2
Total partial rollbacks: 1
Total rollbacks: 3

Summary:
Total transactions left to replicate: 4
Total rows left to replicate: 4
Size of transactions left to replicate: 2.00 KiB
Size of rows left to replicate: 556.00 B
Total inserts remaining: 3
Total partial rollbacks: 5
Total rollbacks: 3

Start LSN = 0.3793736
End LSN = 0.20506624

When you provide the verbose level 3, the information generated includes a transaction analysis that includes a description of the contents of every transaction in every track:

$ ttXactLog -v3 -logAnalyze rep1

Transaction id:    3.10
Track for this xid: 1
Logmarker before this xid: 275
Rows left to replicate: 1
Transaction size: 800.00 B
Size of rows left: 122.00 B
Total inserts remaining: 1

Transaction id:    2.1
Track for this xid: 0
Logmarker before this xid: 276
Rows left to replicate: 1
Transaction size: 368.00 B
Size of rows left: 122.00 B
Total inserts remaining: 1

Transaction id:    2.19
Track for this xid: 1
Logmarker before this xid: 823
Rows left to replicate: 1
Transaction size: 368.00 B
Size of rows left: 122.00 B
Total inserts remaining: 1

Transaction id:    3.2
Track for this xid: 0
Logmarker before this xid: 842
Rows left to replicate: 1
Transaction size: 368.00 B
Size of rows left: 122.00 B
Total inserts remaining: 1

Track analysis for track number: 0
Transactions left to replicate: 2
Rows left to replicate: 2
Size of transactions left to replicate: 736.00 B
Size of rows left to replicate: 244.00 B
Total inserts remaining: 2
Total partial rollbacks: 4

Track analysis for track number: 1
Transactions left to replicate: 2
Rows left to replicate: 2
Size of transactions left to replicate: 1.14 KiB
Size of rows left to replicate: 244.00 B
Total inserts remaining: 2
Total partial rollbacks: 1
Total rollbacks: 3

Summary:
Total transactions left to replicate: 4
Total rows left to replicate: 4
Size of transactions left to replicate: 1.86 KiB
Size of rows left to replicate: 488.00 B
Total inserts remaining: 4
Total partial rollbacks: 5
Total rollbacks: 3

Start LSN = 0.3793736
End LSN = 0.21444608

When you specify the XID, the tool displays verbose level 3 output where the transaction analysis is based on the XID. If an XID is used by two separate transactions, the report shows with the LogMarker entry the nearest point in the transaction log just before the start of each transaction.

$ ttXactLog -logAnalyze -xid 2.19 rep1;

Transaction id:    2.19
Track for this xid: 1
Logmarker before this xid: 823
Rows left to replicate: 1
Transaction size: 368.00 B
Size of rows left: 122.00 B
Total inserts remaining: 1

Track analysis for track number: 0
Transactions left to replicate: 0
Rows left to replicate: 0
Size of transactions left to replicate: 0.00 B
Size of rows left to replicate: 0.00 B

Track analysis for track number: 1
Transactions left to replicate: 1
Rows left to replicate: 1
Size of transactions left to replicate: 368.00 B
Size of rows left to replicate: 122.00 B
Total inserts remaining: 1

Summary:
Total transactions left to replicate: 1
Total rows left to replicate: 1
Size of transactions left to replicate: 368.00 B
Size of rows left to replicate: 122.00 B
Total inserts remaining: 1

Start LSN = 0.3793736
End LSN = 0.20514816

Note:
For more details, see "ttXactLog" in the Oracle TimesTen In-Memory Database Reference.

13 Resolving Replication Conflicts

This chapter includes these topics:

- How replication conflicts occur

- Using a timestamp to resolve conflicts

- Configuring timestamp comparison

- Reporting conflicts

- The conflict report XML Document Type Definition

How replication conflicts occur

Tables in databases configured in a bidirectional replication scheme may be subject to replication conflicts. A replication conflict occurs when applications on bidirectionally replicated databases initiate an update, insert or delete operation on the same data item at the same time. If no special steps are taken, each database can end up in disagreement with the last update made by the other database.

These types of replication conflicts can occur:

- Update conflicts: This type of conflict occurs when concurrently running transactions at different databases make simultaneous update requests on the same row in the same table, and install different values for one or more columns.

- Uniqueness conflicts: This type of conflict occurs when concurrently running transactions at different databases make simultaneous insert requests for a row in the same table that has the same primary or unique key, but different values for one or more other columns.

- Delete conflicts: This type of conflict occurs when a transaction at one database deletes a row while a concurrent transaction at another database simultaneously updates or inserts the same row. Currently, TimesTen can detect delete/update conflicts, but cannot detect delete/insert conflicts. TimesTen cannot resolve either type of delete conflict.

See "Reporting conflicts" for example reports generated by TimesTen upon detecting update, uniqueness, and delete conflicts.

Note:
TimesTen does not detect conflicts involving TRUNCATE TABLE statements.

Update and insert conflicts

Figure 13-1 shows the results from an update conflict, which would occur for the value of X under the following circumstances:

Steps

On Database A

On Database B

Initial condition

X is 1.

X is 1.

The application on each database updates X simultaneously.

Set X=2.

Set X=100.

The replication agent on each database sends its update to the other database.

Replicate X to database B.

Replicate X to database A.

Each database now has the other's update.

Replication says to set X=100.

Replication says to set X=2.

Note:
Uniqueness conflicts resulting from conflicting inserts follow a similar pattern as update conflicts, but the conflict involves the whole row.

Figure 13-1 Update conflict

If update or insert conflicts remain unchecked, the master and subscriber databases fall out of synchronization with each other. It may be difficult or even impossible to determine which database is correct.

With update conflicts, it is possible for a transaction to update many data items but have a conflict on a few of them. Most of the transaction's effects survive the conflict, with only a few being overwritten by replication. If you decide to ignore such conflicts, the transactional consistency of the application data is compromised.

If an update conflict occurs, and if the updated columns for each version of the row are different, then the non-primary key fields for the row may diverge between the replicated tables.

Note:
Within a single database, update conflicts are prevented by the locking protocol: only one transaction at a time can update a specific row in the database. However, update conflicts can occur in replicated systems due to the ability of each database to operate independently.

TimesTen replication uses timestamp-based conflict resolution to cope with simultaneous updates or inserts. Through the use of timestamp-based conflict resolution, you may be able to keep the replicated databases synchronized and transactionally consistent.

Delete/update conflicts

Figure 13-2 shows the results from a delete/update conflict, which would occur for Row 4 under the following circumstances:

Steps

On database A

On database B

Initial condition.

Row 4 exists.

Row 4 exists.

The applications issue a conflicting update and delete on Row 4 simultaneously.

Update Row 4.

Delete Row 4.

The replication agent on each database sends the delete or update to the other.

Replicate update to database B.

Replicate delete to database A.

Each database now has the delete or update from the other database.

Replication says to delete Row 4.

Replication says to update Row 4.

Figure 13-2 Delete/update conflict

Although TimesTen can detect and report delete/update conflicts, it cannot resolve them. Under these circumstances, the master and subscriber databases fall out of synchronization with each other.

Although TimesTen cannot ensure synchronization between databases following such a conflict, it does ensure that the most recent transaction is applied to each database. If the timestamp for the delete is more recent than that for the update, the row is deleted on each database. If the timestamp for the update is more recent than that for the delete, the row is updated on the local database. However, because the row was deleted on the other database, the replicated update is discarded. See "Reporting delete/update conflicts" for example reports.

Note:
There is an exception to this behavior when timestamp comparison is enabled on a table using UPDATE BY USER. See "Enabling user timestamp column maintenance" for details.

Using a timestamp to resolve conflicts

For replicated tables that are subject to conflicts, create the table with a special column of type BINARY(8) to hold a timestamp value that indicates the time the row was inserted or last updated. You can then configure TimesTen to automatically insert a timestamp value into this column each time a particular row is changed, as described in "Configuring timestamp comparison".

Note:
TimesTen does not support conflict resolution between cached tables in a cache group and an Oracle database.

How replication computes the timestamp column depends on your system:

- On UNIX systems, the timestamp value is derived from the timeval structure returned by the gettimeofday system call. This structure reports the time of day in a pair of 4-byte words to a resolution of 1 microsecond. The actual resolution of the value is system-dependent.

- On Windows systems, the timestamp value is derived from the GetSystemTimeAsFileTime Win32 call. The Windows file time is reported in units of 0.1 microseconds, but effective granularity can be as coarse as 10 milliseconds.

TimesTen uses the time value returned by the system at the time the transaction applies each record as the record's insert or update time. Therefore, rows that are inserted or updated by a single transaction may receive different timestamp values.

When applying a transaction received from a master, the replication agent at the subscriber database performs timestamp resolution for insert, update, and delete operations as follows:

- When applying replicated INSERT operations:

- If the timestamp of the transaction record to be applied is newer than the timestamp of the existing row, the existing row is overwritten.

- If the timestamp of the transaction record and the stored record are equal, the insert operation is discarded.

- If the timestamp of the transaction record is older than the timestamp of the stored record, the insert operation from the transaction is discarded.

- If the stored row has been deleted, then no timestamp is available for comparison. A replicated insert operation on a previously deleted row is applied as an insert.

- When applying replicated UPDATE operations:

- If the timestamp of the transaction record to be applied is newer than the timestamp of the stored record, TimesTen applies the update operation to the row.

- If the timestamp of the transaction record and the stored record are equal, the update operation is discarded.

- If the timestamp of the transaction record is older than the timestamp of the stored record, the update operation from the transaction is discarded.

- If the stored row has been deleted, then no timestamp is available for comparison. Any replicated update operations designated for the deleted row are discarded.

- An update operation that cannot find the updated row is considered a delete conflict, which is reported but cannot be resolved.

- When applying replicated DELETE operations:

- If the timestamp of a replicated delete operation is newer than the timestamp of the existing row, the existing row is deleted.

- If the timestamp of a replicated delete operation is older than the timestamp of the stored record (the row has been modified recently), the delete operation is rejected.

Note:
If the ON EXCEPTION NO ACTION clause is specified for a table, then the update, insert, or delete operation that fails a timestamp comparison is rejected. This may result in transactional inconsistencies if replication applies some (but not all) of the actions of a transaction. If the ON EXCEPTION ROLLBACK WORK clause is specified for a table (which is also the default), an update operation that fails timestamp comparison causes the entire transaction to be rejected.

Timestamp comparisons for local updates

To maintain synchronization of tables between replicated sites, TimesTen also performs timestamp comparisons for updates performed by local transactions. If an updated table is declared to have automatic timestamp maintenance, then updates to records that have timestamps exceeding the current system time are prohibited.

Normally, clocks on replicated systems are synchronized sufficiently to ensure that a locally updated record is given a later timestamp than that in the same record stored on the other systems. Perfect synchronization may not be possible or affordable, but by protecting record timestamps from "going backwards," replication can help to ensure that the tables on replicated systems stay synchronized.

Configuring timestamp comparison

To configure timestamp comparison:

- Include a column in your replicated tables to hold the timestamp value. See "Including a timestamp column in replicated tables".

- Include a CHECK CONFLICTS clause for each TABLE element in the CREATE REPLICATION statement to identify the timestamp column, how timestamps are to be generated, what to do in the event of a conflict, and how to report conflicts. See "Configuring the CHECK CONFLICTS clause".

Including a timestamp column in replicated tables

To use timestamp comparison on replicated tables, you must specify a nullable column of type BINARY(8) to hold the timestamp value. The timestamp column must be created along with the table as part of a CREATE TABLE statement. It cannot be added later as part of an ALTER TABLE statement. In addition, the timestamp column cannot be part of a primary key or index. Example 13-1 shows that the rep.tab table contains a column named tstamp of type BINARY(8) to hold the timestamp value.

Example 13-1 Including a timestamp column when creating a table

CREATE TABLE rep.tab (col1 NUMBER NOT NULL,
col2 NUMBER NOT NULL,
tstamp BINARY(8),
PRIMARY KEY (col1));

If no timestamp column is defined in the replicated table, timestamp comparison cannot be performed to detect conflicts. Instead, at each site, the value of a row in the database reflects the most recent update applied to the row, either by local applications or by replication.

Configuring the CHECK CONFLICTS clause

When configuring your replication scheme, you can set up timestamp comparison for a TABLE element by including a CHECK CONFLICTS clause in the table's element description in the CREATE REPLICATION statement.

Note:
A CHECK CONFLICT clause cannot be specified for DATASTORE elements.

For more details on the syntax, see "CREATE REPLICATION" statement and "CHECK CONFLICTS" clause in the Oracle TimesTen In-Memory Database SQL Reference. Example 13-2 shows how CHECK CONFLICTS might be used when configuring your replication scheme.

Example 13-2 Automatic timestamp comparison

In this example, we establish automatic timestamp comparison for the bidirectional replication scheme defined in Example 9-10. The DSNs, west_dsn and east_dsn, define the westds and eastds databases that replicate the repl.accounts table containing the tstamp timestamp table. In the event of a comparison failure, discard the transaction that includes an update with the older timestamp.

CREATE REPLICATION r1
ELEMENT elem_accounts_1 TABLE accounts
CHECK CONFLICTS BY ROW TIMESTAMP
COLUMN tstamp
UPDATE BY SYSTEM
ON EXCEPTION ROLLBACK WORK
MASTER westds ON "westcoast"
SUBSCRIBER eastds ON "eastcoast"
ELEMENT elem_accounts_2 TABLE accounts
CHECK CONFLICTS BY ROW TIMESTAMP
COLUMN tstamp
UPDATE BY SYSTEM
ON EXCEPTION ROLLBACK WORK
MASTER eastds ON "eastcoast"
SUBSCRIBER westds ON "westcoast";

When bidirectionally replicating databases with conflict resolution, the replicated tables on each database must be set with the same CHECK CONFLICTS attributes. If you need to disable or change the CHECK CONFLICTS settings for the replicated tables, use the ALTER REPLICATION statement described in "Eliminating conflict detection in a classic replication scheme" and apply to each replicated database.

Enabling system timestamp column maintenance

Enable system timestamp comparison by using:

CHECK CONFLICTS BY ROW TIMESTAMP
COLUMN ColumnName
UPDATE BY SYSTEM

TimesTen automatically maintains the value of the timestamp column using the current time returned by the underlying operating system. This is the default setting.

When you specify UPDATE BY SYSTEM, TimesTen:

- Initializes the timestamp column to the current time when a new record is inserted into the table.

- Updates the timestamp column to the current time when an existing record is modified.

During initial load, the timestamp column values should be left NULL, and applications should not give a value for the timestamp column when inserting or updating a row.

When you use the ttBulkCp or ttMigrate utility to save TimesTen tables, the saved rows maintain their current timestamp values. When the table is subsequently copied or migrated back into TimesTen, the timestamp column retains the values it had when the copy or migration file was created.

Note:
If you configure TimesTen for timestamp comparison after using the ttBulkCp or ttMigrate to copy or migrate your tables, the initial values of the timestamp columns remain NULL, which is considered by replication to be the earliest possible time.

Enabling user timestamp column maintenance

Enable user timestamp column maintenance on a table by using:

CHECK CONFLICTS BY ROW TIMESTAMP
COLUMN ColumnName
UPDATE BY USER

When you configure UPDATE BY USER, your application is responsible for maintaining timestamp values. The timestamp values used by your application can be arbitrary, but the time values cannot decrease. In cases where the user explicitly sets or updates the timestamp column, the application-provided value is used instead of the current time.

Replicated delete operations always carry a system-generated timestamp. If replication has been configured with UPDATE BY USER and an update/delete conflict occurs, the conflict is resolved by comparing the two timestamp values and the operation with the larger timestamp wins. If the basis for the user timestamp varies from that of the system-generated timestamp, the results may not be as expected. Therefore, if you expect delete conflicts to occur, use system-generated timestamps.

Reporting conflicts

TimesTen conflict checking may be configured to report conflicts to a human-readable plain text file, or to an XML file for use by user applications. This section includes the topics:

- Reporting conflicts to a text file

- Reporting conflicts to an XML file

- Reporting uniqueness conflicts

- Reporting update conflicts

- Reporting delete/update conflicts

- Suspending and resuming the reporting of conflicts

Reporting conflicts to a text file

To configure replication to report conflicts to a human-readable text file (the default), use:

CHECK CONFLICTS BY ROW TIMESTAMP
COLUMN ColumnName
...
REPORT TO 'FileName' FORMAT STANDARD

An entry is added to the report file FileName that describes each conflict. The phrase FORMAT STANDARD is optional and may be omitted, as the standard report format is the default.

Each failed operation logged in the report consists of an entry that starts with a header, followed by information specific to the conflicting operation. Each entry is separated by a number of blank lines in the report.

The header contains:

- The time the conflict was discovered.

- The databases that sent and received the conflicting update.

- The table in which the conflict occurred.

The header has the following format:

Conflict detected at time on date
Datastore : subscriber_database
Transmitting name : master_database
Table : username.tablename

For example:

Conflict detected at 20:08:37 on 05-17-2004
Datastore : /tmp/subscriberds
Transmitting name : MASTERDS
Table : USER1.T1

Following the header is the information specific to the conflict. Data values are shown in ASCII format. Binary data is translated into hexadecimal before display, and floating-point values are shown with appropriate precision and scale.

For further description of the conflict report file, see "Reporting uniqueness conflicts", "Reporting update conflicts" and "Reporting delete/update conflicts".

Reporting conflicts to an XML file

To configure replication to report conflicts to an XML file, use:

CHECK CONFLICTS BY ROW TIMESTAMP
COLUMN ColumnName
...
REPORT TO 'FileName' FORMAT XML

Replication uses the base file name FileName to create two files. FileName.xml is a header file that contains the XML Document Type Definition for the conflict report structure, as well as the root element, defined as <ttrepconflictreport>. Inside the root element is an XML directive to include the file FileName.include, and it is to this file that all conflicts are written. Each conflict is written as a single element of type <conflict>.

For further description of the conflict report file XML elements, see "The conflict report XML Document Type Definition".

Note:
When performing log maintenance on an XML conflict report file, only the file FileName.include should be truncated or moved. For conflict reporting to continue to function correctly, the file FileName.xml should be left untouched.

Reporting uniqueness conflicts

A uniqueness conflict record is issued when a replicated insert fails because of a conflict.

A uniqueness conflict record in the report file contains:

- The timestamp and values for the existing tuple, which is the tuple that the conflicting tuple is in conflict with

- The timestamp and values for the conflicting insert tuple, which is the tuple of the insert that failed

- The key column values used to identify the record

- The action that was taken when the conflict was detected (discard the single row insert or the entire transaction)

Note:
If the transaction was discarded, the contents of the entire transaction are logged in the report file.

The format of a uniqueness conflict record is:

Conflicting insert tuple timestamp : <timestamp in binary format>
Existing tuple timestamp : <timestamp in binary format>
The existing tuple :
<<column value> [,<column value>. ..]>
The conflicting tuple :
<<column value> [,<column value> ...]>
The key columns for the tuple:
<<key column name> : <key column value>>
Transaction containing this insert skipped
Failed transaction:
Insert into table <user>.<table> <<columnvalue> [,<columnvalue>...]>
End of failed transaction

Example 13-3 shows the output from a uniqueness conflict on the row identified by the primary key value, '2'. The older insert replicated from subscriberds conflicts with the newer insert in masterds, so the replicated insert is discarded.

Example 13-3 Output from uniqueness conflict

Conflict detected at 13:36:00 on 03-25-2002
Datastore : /tmp/masterds
Transmitting name : SUBSCRIBERDS
Table : TAB
Conflicting insert tuple timestamp : 3C9F983D00031128
Existing tuple timestamp : 3C9F983E000251C0
The existing tuple :
< 2, 2, 3C9F983E000251C0>
The conflicting tuple :
< 2, 100, 3C9F983D00031128>
The key columns for the tuple:
<COL1 : 2>
Transaction containing this insert skipped
Failed transaction:
Insert into table TAB < 2, 100, 3C9F983D00031128>
End of failed transaction

Reporting update conflicts

An update conflict record is issued when a replicated update fails because of a conflict. This record reports:

- The timestamp and values for the existing tuple, which is the tuple that the conflicting tuple is in conflict with.

- The timestamp and values for the conflicting update tuple, which is the tuple of the update that failed.

- The old values, which are the original values of the conflicting tuple before the failed update.

- The key column values used to identify the record.

- The action that was taken when the conflict was detected (discard the single row update or the entire transaction).

Note:
If the transaction was discarded, the contents of the entire transaction are logged in the report file.

The format of an update conflict record is:

Conflicting update tuple timestamp : <timestamp in binary format>
Existing tuple timestamp : <timestamp in binary format>
The existing tuple :
<<column value> [,<column value>. ..]>
The conflicting update tuple :
TSTAMP :<timestamp> :<<column value> [,<column value>. ..]>
The old values in the conflicting update:
TSTAMP :<timestamp> :<<column value> [,<column value>. ..]>
The key columns for the tuple:
<<key column name> : <key column value>>
Transaction containing this update skipped
Failed transaction:
Update table <user>.<table> with keys:
<<key column name> : <key column value>>
New tuple value:
<TSTAMP :<timestamp> :<<column value> [,<column value>. ..]>
End of failed transaction

Example 13-4 shows the output from an update conflict on the col2 value in the row identified by the primary key value, '6'. The older update replicated from the masterds database conflicts with the newer update in subscriberds, so the replicated update is discarded.

Example 13-4 Output from an update conflict

Conflict detected at 15:03:18 on 03-25-2002
Datastore : /tmp/subscriberds
Transmitting name : MASTERDS
Table : TAB
Conflicting update tuple timestamp : 3C9FACB6000612B0
Existing tuple timestamp : 3C9FACB600085CA0
The existing tuple :
< 6, 99, 3C9FACB600085CA0>
The conflicting update tuple :
<TSTAMP :3C9FACB6000612B0, COL2 : 50>
The old values in the conflicting update:
<TSTAMP :3C9FAC85000E01F0, COL2 : 2>
The key columns for the tuple:
<COL1 : 6>
Transaction containing this update skipped
Failed transaction:
Update table TAB with keys:
<COL1 : 6>
New tuple value: <TSTAMP :3C9FACB6000612B0, COL2 : 50>
End of failed transaction

Reporting delete/update conflicts

A delete/update conflict record is issued when an update is attempted on a row that has more recently been deleted. This record reports:

- The timestamp and values for the conflicting update tuple or conflicting delete tuple, whichever tuple failed.

- If the delete tuple failed, the report also includes the timestamp and values for the existing tuple, which is the surviving update tuple with which the delete tuple was in conflict.

- The key column values used to identify the record.

- The action that was taken when the conflict was detected (discard the single row update or the entire transaction).

Note:
If the transaction was discarded, the contents of the entire transaction are logged in the report file. TimesTen cannot detect delete/insert conflicts.

The format of a record that indicates a delete conflict with a failed update is:

Conflicting update tuple timestamp : <timestamp in binary format>
The conflicting update tuple :
TSTAMP :<timestamp> :<<column value> [,<column value>. ..]>
This transaction skipped
The tuple does not exist
Transaction containing this update skipped
Update table <user>.<table> with keys:
<<key column name> : <key column value>>
New tuple value:
<TSTAMP :<timestamp> :<<column value> [,<column value>. ..]>
End of failed transaction

Example 13-5 shows the output from a delete/update conflict caused by an update on a row that has more recently been deleted. Because there is no row to update, the update from SUBSCRIBERDS is discarded.

Example 13-5 Output from a delete/update conflict: delete is more recent

Conflict detected at 15:27:05 on 03-25-2002
Datastore : /tmp/masterds
Transmitting name : SUBSCRIBERDS
Table : TAB
Conflicting update tuple timestamp : 3C9FB2460000AFC8
The conflicting update tuple :
<TSTAMP :3C9FB2460000AFC8, COL2 : 99>
The tuple does not exist
Transaction containing this update skipped
Failed transaction:
Update table TAB with keys:
<COL1 : 2>
New tuple value: <TSTAMP :3C9FB2460000AFC8,
COL2 : 99>
End of failed transaction

The format of a record that indicates an update conflict with a failed delete is:

Conflicting binary delete tuple timestamp : <timestamp in binary format>
Existing binary tuple timestamp : <timestamp in binary format>
The existing tuple :
<<column value> [,<column value>. ..]>
The key columns for the tuple:
<<key column name> : <key column value>>
Transaction containing this delete skipped
Failed transaction:
Delete table <user>.<table> with keys:
<<key column name> : <key column value>>
End of failed transaction

Example 13-6 shows the output from a delete/update conflict caused by a delete on a row that has more recently been updated. Because the row was updated more recently than the delete, the delete from masterds is discarded.

Example 13-6 Output from a delete/update conflict: update is more recent

Conflict detected at 15:27:20 on 03-25-2002
Datastore : /tmp/subscriberds
Transmitting name : MASTERDS
Table : TAB
Conflicting binary delete tuple timestamp : 3C9FB258000708C8
Existing binary tuple timestamp : 3C9FB25800086858
The existing tuple :
< 147, 99, 3C9FB25800086858>
The key columns for the tuple:
<COL1 : 147>
Transaction containing this delete skipped
Failed transaction:
Delete table TAB with keys:
<COL1 : 147>

Suspending and resuming the reporting of conflicts

Provided your applications are well-behaved, replication usually encounters and reports only sporadic conflicts. However, it is sometimes possible under heavy load to trigger a flurry of conflicts in a short amount of time, particularly when applications are in development and such errors are expected. This can potentially have a negative impact on the performance of the host because of excessive writes to the conflict report file and the large number of SNMP traps that can be generated.

To avoid overwhelming a host with replication conflicts, you can configure replication to suspend conflict reporting when the number of conflicts per second has exceeded a user-specified threshold. Conflict reporting may also be configured to resume once the conflicts per second have fallen below a user-specified threshold.

Conflict reporting suspension and resumption can be detected by an application by catching the SNMP traps ttRepConflictReportStoppingTrap and ttRepConflictReportStartingTrap, respectively. See "Diagnostics through SNMP Traps" in Oracle TimesTen In-Memory Database Error Messages and SNMP Traps for more information.

To configure conflict reporting to be suspended and resumed based on the number of conflicts per second, use the CONFLICT REPORTING SUSPEND AT and CONFLICT REPORTING RESUME AT attributes for the STORE clause of a replication scheme.

If the replication agent is stopped while conflict reporting is suspended, conflict reporting is enabled when the replication agent is restarted. The SNMP trap ttRepConflictReportingStartingTrap is not sent if this occurs. This means that an application that monitors the conflict report suspension traps must also monitor the traps for replication agent stopping and starting.

If you set CONFLICT REPORTING RESUME AT to 0, reporting does not resume until the replication agent is restarted.

Example 13-7 demonstrates the configuration of a replication schemes where conflict reporting ceases when the number of conflicts exceeds 20 per second, and conflict reporting resumes when the number of conflicts drops below 10 per second.

Example 13-7 Configuring conflict reporting thresholds

CREATE REPLICATION r1
ELEMENT elem_accounts_1 TABLE accounts
CHECK CONFLICTS BY ROW TIMESTAMP
COLUMN tstamp
UPDATE BY SYSTEM
ON EXCEPTION ROLLBACK WORK
REPORT TO 'conflicts' FORMAT XML
MASTER westds ON "westcoast"
SUBSCRIBER eastds ON "eastcoast"
ELEMENT elem_accounts_2 TABLE accounts
CHECK CONFLICTS BY ROW TIMESTAMP
COLUMN tstamp
UPDATE BY SYSTEM
ON EXCEPTION ROLLBACK WORK
REPORT TO 'conflicts' FORMAT XML
MASTER eastds ON "eastcoast"
SUBSCRIBER westds ON "westcoast"
STORE westds ON "westcoast"
CONFLICT REPORTING SUSPEND AT 20
CONFLICT REPORTING RESUME AT 10
STORE eastds ON "eastcoast"
CONFLICT REPORTING SUSPEND AT 20
CONFLICT REPORTING RESUME AT 10;

The conflict report XML Document Type Definition

The TimesTen XML format conflict report is are based on the XML 1.0 specification (http://www.w3.org/TR/REC-xml). The XML Document Type Definition (DTD) for the replication conflict report is a set of markup declarations that describes the elements and structure of a valid XML file containing a log of replication conflicts. This DTD can be found in the XML header file, identified by the suffix .xml, that is created when replication is configured to report conflicts to an XML file. User applications which understand XML use the DTD to parse the rest of the XML replication conflict report. For more information on reading and understanding XML Document Type Definitions, see http://www.w3.org/TR/REC-xml.

<?xml version="1.0"?>
<!DOCTYPE ttreperrorlog [
<!ELEMENT ttrepconflictreport(conflict*) >
<!ELEMENT repconflict        (header, conflict, scope, failedtransaction) >
<!ELEMENT header             (time, datastore, transmitter, table) >
<!ELEMENT time               (hour, min, sec, year, month, day) >
<!ELEMENT hour               (#PCDATA) >
<!ELEMENT min                (#PCDATA) >
<!ELEMENT sec                (#PCDATA) >
<!ELEMENT year               (#PCDATA) >
<!ELEMENT month              (#PCDATA) >
<!ELEMENT day                (#PCDATA) >
<!ELEMENT datastore          (#PCDATA) >
<!ELEMENT transmitter        (#PCDATA) >
<!ELEMENT table              (tableowner, tablename) >
<!ELEMENT tableowner          (#PCDATA) >
<!ELEMENT tablename          (#PCDATA) >
<!ELEMENT scope              (#PCDATA) >
<!ELEMENT failedtransaction  ((insert | update | delete)+) >
<!ELEMENT insert             (sql) >
<!ELEMENT update             (sql, keyinfo, newtuple) >
<!ELEMENT delete             (sql, keyinfo) >
<!ELEMENT sql                (#PCDATA) >
<!ELEMENT keyinfo            (column+) >
<!ELEMENT newtuple           (column+) >
<!ELEMENT column             (columnname, columntype, columnvalue) >
<!ATTLIST column
pos CDATA #REQUIRED >
<!ELEMENT columnname         (#PCDATA) >
<!ELEMENT columnvalue        (#PCDATA) >
<!ATTLIST columnvalue
isnull (true | false) "false">
<!ELEMENT existingtuple       (column+) >
<!ELEMENT conflictingtuple    (column+) >
<!ELEMENT conflictingtimestamp(#PCDATA) >
<!ELEMENT existingtimestamp   (#PCDATA) >
<!ELEMENT oldtuple            (column+) >
<!ELEMENT conflict            (conflictingtimestamp, existingtimestamp*,
existingtuple*, conflictingtuple*,
oldtuple*, keyinfo*) >
<!ATTLIST conflict
type (insert | update | deletedupdate | updatedeleted) #REQUIRED>
<!ENTITY logFile                  SYSTEM "Filename.include">
]>
<ttrepconflictreport>
&logFile;
</ttrepconflictreport>

The main body of the document

The .xml file for the XML replication conflict report is merely a header, containing the XML Document Type Definition that describes the report format and links to a file with the suffix .include. This include file is the main body of the report, containing each replication conflict as a separate element. There are three possible types of elements: insert, update and delete/update conflicts. Each conflict type requires a slightly different element structure.

The uniqueness conflict element

A uniqueness conflict occurs when a replicated insertion fails because a row with an identical key column was inserted more recently. See "Reporting uniqueness conflicts" for a description of the information that is written to the conflict report for a uniqueness conflict.

Example 13-8 illustrates the format of a uniqueness conflict XML element, using the values from Example 13-3.

Example 13-8 Uniqueness conflict element

<repconflict>
<header>
<time>
<hour>13</hour>
<min>36</min>
<sec>00</sec>
<year>2002</year> <month>03</month>
<day>25</day>
</time>
<datastore>/tmp/masterds</datastore>
<transmitter>SUBSCRIBERDS</transmitter>
<table>
<tableowner>REPL</tableowner>
<tablename>TAB</tablename>
</table>
</header>
<conflict type="insert">
<conflictingtimestamp>3C9F983D00031128</conflictingtimestamp>
<existingtimestamp>3C9F983E000251C0</existingtimestamp>
<existingtuple>
<column pos="1">
<columnname>COL1</columnname>
<columntype>NUMBER(38)</columntype>
<columnvalue>2</columnvalue>
</column>
<column pos="2">
<columnname>COL2</columnname>
<columntype>NUMBER(38)</columntype>
<columnvalue>2</columnvalue>
</column>
<columnname>TSTAMP</columnname>
<columntype>BINARY(8)</columntype>
<columnvalue>3C9F983E000251C0</columnvalue>
</column>
</existingtuple>
<conflictingtuple>
<column pos="1">
<columnname>COL1</columnname>
<columntype>NUMBER(38)</columntype>
<columnvalue>2</columnvalue>
</column>
<column pos="2">
<columnname>COL2</columnname>
<columntype>NUMBER(38)</columntype>
<columnvalue>100</columnvalue>
</column>
<column pos="3">
<columname>TSTAMP</columnname>
<columntype>BINARY(8)</columntype>
<columnvalue>3C9F983D00031128</columnvalue>
</column>
</conflictingtuple>
<keyinfo>
<column pos="1">
<columnname>COL1</columnname>
<columntype>NUMBER(38)</columntype>
<columnvalue>2</columnvalue>
</column>
</keyinfo>
</conflict>
<scope>TRANSACTION</scope>
<failedtransaction>
<insert>
<sql>Insert into table TAB </sql>
<column pos="1">
<columnname>COL1</columnname>
<columntype>NUMBER(38)</columntype>
<columnvalue>2</columnvalue>
</column>
<column pos="2">
<columnname>COL2</columnname>
<columntype>NUMBER(38)</columntype>
<columnvalue>100</columnvalue>
</column>
<column pos="3">
<columnname>TSTAMP</columnname>
<columntype>NUMBER(38)</columntype>
<columnvalue>3C9F983D00031128</columnvalue>
</column>
</insert>
</failedtransaction>
</repconflict>

The update conflict element

An update conflict occurs when a replicated update fails because the row was updated more recently. See "Reporting update conflicts" for a description of the information that is written to the conflict report for an update conflict.

Example 13-9 illustrates the format of an update conflict XML element, using the values from Example 13-4.

Example 13-9 Update conflict element

<repconflict>
<header>
<time>
<hour>15</hour>
<min>03</min>
<sec>18</sec>
<year>2002</year>
<month>03</month>
<day>25</day>
</time>
<datastore>/tmp/subscriberds</datastore>
<transmitter>MASTERDS</transmitter>
<table>
<tableowner>REPL</tableowner>
<tablename>TAB</tablename>
</table>
</header>
<conflict type="update">
<conflictingtimestamp>
3C9FACB6000612B0
</conflictingtimestamp>
<existingtimestamp>3C9FACB600085CA0</existingtimestamp>
<existingtuple>
<column pos="1">
<columnname>COL1</columnname>
<columntype>NUMBER(38)</columntype>
<columnvalue>6</columnvalue>
</column>
<column pos="2">
<columnname>COL2</columname>
<columntype>NUMBER(38)</columntype>
<columnvalue>99</columnvalue>
</column>
<column pos="3">
<columnname>TSTAMP</columnname>
<columntype>BINARY(8)</columntype>
<columnvalue>3C9FACB600085CA0></columnvalue>
</column>
</existingtuple>
<conflictingtuple>
<column pos="3">
<columnname>TSTAMP</columnname>
<columntype>BINARY(8)</columntype>
<columnvalue>3C9FACB6000612B0</columnvalue>
</column>
<column pos="2">
<columnname>COL2</columnname>
<columntype>NUMBER(38)</columntype>
<columnvalue>50</columnvalue>
</column>
</conflictingtuple>
<oldtuple>
<column pos="3">
<columnname>TSTAMP</columnname>
<columntype>BINARY(8)</columntype>
<columnvalue>3C9FAC85000E01F0</columnvalue>
</column>
<column pos="2">
<columnname>COL2</columnname>
<columntype>NUMBER(38)</columntype>
<columnvalue>2</columnvalue>
</column>
</oldtuple>
<keyinfo>
<column pos="1">
<columnname>COL1</columnname>
<columntype>NUMBER(38)</columntype>
<columnvalue>6</columnvalue>
</column>
</keyinfo>
</conflict>
<scope>TRANSACTION</scope>
<failedtransaction>
<update>
<<sql>Update table TAB</sql>
<<keyinfo>
<column pos="1">
<columnname>COL1</columnname>
<columntype>NUMBER(38)</columntype>
<columnvalue>6</columnvalue>
</column>
</keyinfo>
<column pos="3">
<columnname>TSTAMP</columnname>
<columntype>BINARY(8)</columntype>
<columnvalue>3C9FACB6000612B0</columnvalue>
</column>
<column pos="2">
<columnname>COL2</columnname>
<columntype>NUMBER(38)</columntype>
<columnvalue>50</columnvalue>
</column>
</update>
</failedtransaction>
</repconflict>

The delete/update conflict element

A delete/update conflict occurs when a replicated update fails because the row to be updated has already been deleted on the database receiving the update, or when a replicated deletion fails because the row has been updated more recently. See "Reporting delete/update conflicts" for a description of the information that is written to the conflict report for a delete/update conflict.

Example 13-10 illustrates the format of a delete/update conflict XML element in which an update fails because the row has been deleted more recently, using the values from Example 13-5.

Example 13-10 Delete/update conflict element: delete is more recent

<repconflict>
<header>
<time>
<hour>15</hour>
<min>27</min>
<sec>05</sec>
<year>2002</year>
<month>03</month>
<day>25</day>
</time>
<datastore>/tmp/masterds</datastore>
<transmitter>SUBSCRIBERDS</transmitter>
<table>
<tableowner>REPL</tableowner>
<tablename>TAB</tablename>
</table>
</header>
<conflict type="update">
<conflictingtimestamp>
3C9FB2460000AFC8
</conflictingtimestamp>
<conflictingtuple>
<column pos="3">
<columnname>TSTAMP</columnname>
<columntype>BINARY(8)</columntype>
<columnvalue>3C9FB2460000AFC8</columnvalue>
</column>
<column pos="2">
<columnname>COL2</columnname>
<columntype>NUMBER(38)</columntype>
<columnvalue>99/columnvalue>
</column>
</conflictingtuple>
<keyinfo>
<column pos="1">
<columnname>COL1</columnname>
<columntype>NUMBER(38)</columntype>
<columnvalue>2</columnvalue>
</column>
</keyinfo>
</conflict>
<scope>TRANSACTION</scope>
<failedtransaction>
<update>
<sql>Update table TAB</sql>
<keyinfo>
<column pos="1">
<columnname>COL1</columnname>
<columntype>NUMBER(38)</columntype>
<columnvalue>2</columnvalue>
</column>
</keyinfo>
<column pos="3">
<columnname>TSTAMP</columnname>
<columntype>BINARY(8)</columntype>
<columnvalue>3C9FB2460000AFC8</columnvalue>
</column>
<column pos="2">
<columnname>COL2</columnname>
<columntype>NUMBER(38)</columntype>
<columnvalue>99</columnvalue>
</column>
</update>
</failedtransaction>
</repconflict>

Example 13-11 illustrates the format of a delete/update conflict XML element in which a deletion fails because the row has been updated more recently, using the values from Example 13-6.

Example 13-11 Delete/update conflict element: update is more recent

<repconflict>
<header>
<time>
<hour>15</hour>
<min>27</min>
<sec>20</sec>
<year>2002</year>
<month>03</month>
<day>25</day>
</time>
<datastore>/tmp/masterds</datastore>
<transmitter>MASTERDS</transmitter>
<table>
<tableowner>REPL</tableowner>
<tablename>TAB</tablename>
</table>
</header>
<conflict type="delete">
<conflictingtimestamp>
3C9FB258000708C8
</conflictingtimestamp>
<existingtimestamp>3C9FB25800086858</existingtimestamp>
<existingtuple>
<column pos="1">
<columnname>COL1</columnname>
<columntype>NUMBER(38)</columntype>
<columnvalue>147</columnvalue>
</column>
<column pos="2">
<columnname>COL2</columnname>
<columntype>NUMBER(38)</columntype>
<columnvalue>99</columnvalue>
</column>
<column pos="3">
<columnname>TSTAMP</columnname>
<columntype>BINARY(8)</columntype>
<columnvalue>3C9FB25800086858</columnvalue>
</column>
</existingtuple>
<keyinfo>
<column pos="1">
<columnname>COL1</columnname>
<columntype>NUMBER(38)</columntype>
<columnvalue>147</columnvalue>
</column>
</keyinfo>
</conflict>
<scope>TRANSACTION</scope>
<failedtransaction>
<delete>
<sql>Delete from table TAB</sql>
<keyinfo>
<column pos="1">
<columnname>COL1</columnname>
<columntype>NUMBER(38)</columntype>
<columnvalue>147</columnvalue>
</column>
</keyinfo>
</delete>
</failedtransaction>
</repconflict>

14 Improving Replication Performance

The following describes methods for increasing replication performance:

- Configure parallel replication. See "Configuring parallel replication".

- Use asynchronous replication, which is the default. For more information, see "Making decisions about performance and recovery tradeoffs". However, if you are using active standby pairs, return twosafe (synchronous replication) has better performance than return receipt (semi-synchronous replication).

- Set the LogFileSize and LogBufMB first connection attributes to their maximum values. For more information, see "Setting connection attributes for logging".

- If the workload is heavy enough that replication sometimes falls behind, replicated changes must be captured from the transaction logs on disk rather than from the in-memory log buffer. Using the fastest possible storage for the TimesTen transaction logs reduces I/O contention between transaction log flushing and replication capture and helps replication to catch up more quickly during periods of reduced workload. Consider using a high performance, cached disk array using a RAID-0 stripe across multiple fast disks or solid state storage.

- Experiment with the number of connections to the database where the updates are applied. If you need more than 64 concurrent connections, set the Connections first connection attribute to a higher value. See "Connections" in Oracle TimesTen In-Memory Database Reference.

- Adjust the transaction log buffer size and CPU power and resources. See "Adjust transaction log buffer size and CPU".

- There can be performance issues after altering tables with multiple partitions and extraneous space. For more information, see "Performance considerations when altering tables that are replicated".

- Increase the number of threads that apply changes from the active master database to the standby master database by altering the RecoveryThreads first connection attribute. For details, see "Increase replication throughput for active standby pairs".

- Replication and XLA operations have significant overhead with transaction logging. Replication scales best when there are a limited number of transmitters or receivers. For more information, see "Limit replication transmitters, receivers, and XLA readers".

Note:
Additional recommendations can be found in "Poor replication or XLA performance" in Oracle TimesTen In-Memory Database Troubleshooting Guide.

Adjust transaction log buffer size and CPU

If you are planning a replication scheme, ensure the following:

- The transaction log setting for LogBufMB should result in the value of LOG_FS_READS in the SYS.MONITOR table being 0 or close to 0. This ensures that the replication agent does not have to read any transaction log records from disk. If the value of LOG_FS_READS is increasing, then increase the transaction log buffer size.

- CPU resources are adequate. The replication agent on the master database spawns a thread for every subscriber database. Each thread reads and processes the transaction log independently and needs adequate CPU resources to make progress.

- If the sending side and receiving side of the replication scheme are mismatched in CPU power, place the replication receiver on the faster system.

Performance considerations when altering tables that are replicated

Altering a table to add or remove columns may lead to performance degradation or poor space utilization.

- When you alter a table to add one or more columns, the table is allocated a new partition for the additional columns. The additional partition causes extra processing when retrieving the data, resulting in reduced performance. See "ALTER TABLE" in the Oracle TimesTen In-Memory Database SQL Reference for more information on understanding how partitions are added when using ALTER TABLE.

- When you alter a table to drop a column, the space is not always freed resulting in poor space utilization.

Any replication scheme defined with the TABLE DEFINITION CHECKING EXACT attribute requires that the physical structure of the table be identical on both master databases in order to be able to replicate operations between them. When using the EXACT table definition checking attribute, the only method to free the extraneous space resulted from dropped columns or eliminate extra partitions resulting from added columns is to drop and re-create the table, and then reload the data into the table.

However, if you create the tables with the TABLE DEFINITION CHECKING RELAXED attribute, then (while they must have the same key definition, number of columns, and column data types) the physical structure does not need to be identical on both master databases. The TABLE DEFINITION CHECKING RELAXED attribute can result in slightly slower performance, but only if the tables on both masters are not identical. The change in performance depends on the workload and the number of partitions and columns in the tables.

To improve performance for databases set with RELAXED, you can use ttMigrate -r -relaxedUpgrade to coalesce tables eliminating extraneous space from dropped columns or multiple partitions that were created when adding columns. This can be performed on one database, while the other database is still up and accepting requests on behalf of the application. You do not have to take both databases involved in replication down at the same time, but can perform ttMigrate -r -relaxedUpgrade on each one individually one after the other. This is optimal for databases where the tables are altered often and where the database can only perform online upgrades.

You can only coalesce partitions and eliminate extraneous space with ttMigrate -r -relaxedUpgrade on replicated tables when the table definition checking to RELAXED. However, if your tables have been using the EXACT attribute, then you can temporarily set table definition checking to RELAXED, consolidate the partitions and space for your tables, and then reset it to EXACT.

For more information on the TABLE DEFINITION CHECKING RELAXED attribute, see "Column definition options for replicated tables".

Note:
You can check if the table has multiple partitions. For details, see the instructions in both the "Understanding partitions when using ALTER TABLE" section detailed within "ALTER TABLE" in the Oracle TimesTen In-Memory Database SQL Reference and "Check partition counts for the tables" in the Oracle TimesTen In-Memory Database Troubleshooting Guide.

Increase replication throughput for active standby pairs

You can increase replication throughput for active standby pairs by configuring parallel replication. By default, replication is performed with a single thread where the nodes in a replication scheme have one log reader, or transmitter thread, on the source database, and one applier, or receiving thread, on the target database. Parallel replication instantiates multiple threads to transmit updates from the source database to the target database and to apply these updates on the target database. For more informtion, see "Configuring parallel replication".

Alternatively, you can use the ReceiverThreads first connection attribute to increase the number of threads that apply changes from the active master database to the standby master database from 1 to 2. If you set ReceiverThreads to 2 on the standby, you should also set it to 2 on the active to maintain increased throughput if there is a failover.

You can also set ReceiverThreads to 2 on one or more read-only subscribers in an active standby pair to increase replication throughput from the standby master database.

Databases must be hosted on systems that are 2-way or larger to take advantage of setting this attribute to 2.

Note:
For more details, see "ReceiverThreads" in the Oracle TimesTen In-Memory Database Reference.

Limit replication transmitters, receivers, and XLA readers

Replication and XLA operations have significant overhead with transaction logging. Replication scales best when there are a limited number of transmitters or receivers. Check your replication topology and see if you can simplify it. Generally, XLA scales best when there are a limited number of readers. If your application has numerous readers, see if you can reduce the number.

Monitor XLA and replication to ensure they are reading from the transaction log buffer rather than from the disk. With a lot of concurrent updates, replication may not keep up. Updates are single-threaded at the subscriber. You can achieve better XLA throughput if the frequency of acknowledgements is reduced.

Estimate the number of readers and transmitters required by checking the values in the LOG_FS_READS and LOG_BUFFER_WAITS columns in the SYS.MONITOR table. The system updates this information each time a connection is made or released and each time a transaction is committed or rolled back.

Setting LogFlushMethod=2 can improve performance of RETURN TWOSAFE replication operations and RETURN RECEIPT with DURABLE TRANSMIT operations.

15 Managing Database Failover and Recovery

This chapter applies to all replication schemes, including active standby pairs. However, TimesTen integration with Oracle Clusterware is the best way to monitor active standby pairs. See Chapter 8, "Using Oracle Clusterware to Manage Active Standby Pairs".

This chapter includes these topics:

- Overview of database failover and recovery

- General failover and recovery procedures

- Recovering a failed database

- Recovering nondurable databases

- Writing a failure recovery script

Overview of database failover and recovery

A fundamental element in the design of a highly available system is the ability to recover quickly from a failure. Failures may be related to hardware problems such as system failures or network failures. Software failures include operating system failure, application failure, database failure and operator error.

Your replicated system must employ a cluster manager or custom software to detect such failures and, in the event of a failure involving a master database, redirect the user load to one of its subscribers. The focus of this discussion is on the TimesTen mechanisms that an application or cluster manager can use to recover from failures.

Unless the replication scheme is configured to use the return twosafe service, TimesTen replicates updates only after the original transaction commits to the master database. If a subscriber database is inoperable or communication to a subscriber database fails, updates at the master are not impeded. During outages at subscriber systems, updates intended for the subscriber are saved in the TimesTen transaction log.

Note:
The procedures described in this chapter require the ADMIN privilege.

General failover and recovery procedures

The procedures for managing failover and recovery depend primarily on:

- The replication scheme

- Whether the failure occurred on a master or subscriber database

- Whether the threshold for the transaction log on the master is exhausted before the problem is resolved and the databases reconnected

Subscriber failures

In a default asynchronous replication scheme, if a subscriber database becomes inoperable or communication to a subscriber database fails, updates at the master are not impeded and the cluster manager does not have to take any immediate action.

Note:
If the failed subscriber is configured to use a return service, you must first disable return service blocking, as described in "Managing return service timeout errors and replication state changes".

During outages at subscriber systems, updates intended for the subscriber are saved in the transaction log on the master. If the subscriber agent reestablishes communication with its master before the master reaches its FAILTHRESHOLD, the updates held in the log are automatically transferred to the subscriber and no further action is required. See "Setting the transaction log failure threshold" for details on how to establish the FAILTHRESHOLD value for the master database.

If the FAILTHRESHOLD is exceeded, the master sets the subscriber to the failed state and it must be recovered, as described in "Recovering a failed database". Any application that connects to the failed subscriber receives a tt_ErrReplicationInvalid (8025) warning indicating that the database has been marked failed by a replication peer.

An application can use the ODBC SQLGetInfo function to check if the subscriber database it is connected to has been set to the failed state. The SQLGetInfo function includes a TimesTen-specific infotype, TT_REPLICATION_INVALID, that returns a 32-bit integer value of '1' if the database is failed, or '0' if not failed.

Note:
Since the infotype TT_REPLICATION_INVALID is specific to TimesTen, all applications using it need to include the timesten.h file in addition to the other ODBC include files.

However, if you are using bidirectional replication scheme where each database serves as both master and subscriber and one of the subscribers fail, then an error condition may occur. For example, assuming that the masters and subscribers for the bidirectional replication scheme are defined as follows:

CREATE REPLICATION r1
ELEMENT elem_accounts_1 TABLE ttuser.accounts
MASTER westds ON "westcoast"
SUBSCRIBER eastds ON "eastcoast"
ELEMENT elem_accounts_2 TABLE ttuser.accounts
MASTER eastds ON "eastcoast"
SUBSCRIBER westds ON "westcoast";

- If the eastds subscriber fails, the westds master stops accumulating updates for this subscriber since it received a failure.

- When the eastds subscriber fails, the replication agent shuts down on eastds. However, the eastds master continues accumulating updates to propagate to its subscriber on westds unaware that the replication agent has shut down. These updates continue to accumulate past the defined FAILTHRESHOLD since the replication agent (who propagates the records to the subscriber as well as monitors the FAILTHRESHOLD) is down.

When you are using a bidirectional replication scheme and TT_REPLICATION_INVALID is set to 1 on the failed database, perform the following:

1. Destroy the failed database (in this example, the eastds database).

2. Re-create the failed database by performing a ttRepAdmin -duplicate operation from the other master in the bidirectional replication scheme (in this example, the master on westds).

Example 15-1 Checking whether a database has been set to the failed state

Check if the database identified by the hdbc handle has been set to the failed state.

SQLINTEGER retStatus;

SQLGetInfo(hdbc, TT_REPLICATION_INVALID,
(PTR)&retStatus, NULL, NULL);

Master failures

The cluster manager plays a more central role if a failure involves the master database. If a master database fails, the cluster manager must detect this event and redirect the user load to one of its surviving databases. This surviving subscriber then becomes the master, which continues to accept transactions and replicates them to the other surviving subscriber databases. If the failed master and surviving subscriber are configured in a bidirectional manner, transferring the user load from a failed master to a subscriber does not require that you make any changes to your replication scheme. However, when using unidirectional replication or complex schemes, such as those involving propagators, you may have to issue one or more ALTER REPLICATION statements to reconfigure the surviving subscriber as the "new master" in your scheme. See "Replacing a master database in a classic replication scheme" for an example.

When the problem is resolved, if you are not using the bidirectional configuration or the active standby pair described in "Automatic catch-up of a failed master database", you must recover the master database as described in "Recovering a failed database".

After the database is back online, the cluster manager can either transfer the user load back to the original master or reestablish it as a subscriber for the "acting master."

Automatic catch-up of a failed master database

The master catch-up feature automatically restores a failed master database from a subscriber database without the need to invoke the ttRepAdmin -duplicate operation described in "Recovering a failed database".

The master catch-up feature needs no configuration, but it can be used only in the following types of configurations:

- A single master replicated in a bidirectional manner to a single subscriber

- An active standby pair that is configured with RETURN TWOSAFE

For replication schemes that are not active standby pairs, the following must be true:

- The ELEMENT type is DATASTORE.

- TRANSMIT NONDURABLE or RETURN TWOSAFE must be enabled.

- All replicated transactions must be committed nondurably. They must be transmitted to the remote database before they are committed on the local database. For example, if the replication scheme is configured with RETURN TWOSAFE BY REQUEST and any transaction is committed without first enabling RETURN TWOSAFE, master catch-up may not occur after a failure of the master.

When the master replication agent is restarted after a crash or invalidation, any lost transactions that originated on the master are automatically reapplied from the subscriber to the master (or from the standby to the active in an active standby pair). No connections are allowed to the master database until it has completely caught up with the subscriber. Applications attempting to connect to a database during the catch-up phase receive an error that indicates a catch-up is in progress. The only exception is connecting to a database with the ForceConnect first connection attribute set in the DSN.

When the catch-up phase is complete, the application can connect to the database. An SNMP trap and message to the system log indicate the completion of the catch-up phase.

If one of the databases is invalidated or crashes during the catch-up process, the catch-up phase is resumed when the database comes back up.

Master catch-up can fail under these circumstances:

- The failed database is offline long enough for the failure threshold to be exceeded on the subscriber database (the standby database in an active standby pair).

- Dynamic load operations are taking place on the active database in an active standby pair when the failure occurs. RETURN TWOSAFE is not enabled for dynamic load operations even though it is enabled for the active database. The database failure causes the dynamic load transactions to be trapped and RETURN TWOSAFE to fail.

When master catch-up is required for an active standby pair

TimesTen error 8110 (Connection not permitted. This store requires Master Catchup.) indicates that the standby database is ahead of the active database and that master catch-up must occur before replication can resume.

When using master catch-up with an active standby pair, the standby database must be failed over to become the new active database. If the old active database can recover, it becomes the new standby database. If it cannot recover, the old active database must be destroyed and the new standby database must be created by duplicating the new active database. See "When replication is return twosafe" for more information about recovering from a failure of the active database when RETURN TWOSAFE is configured (required for master catch-up).

In an active standby pair with RETURN TWOSAFE configured, it is possible to have a trapped transaction. A trapped transaction occurs when the new standby database has a transaction present that is not present on the new active database after failover. Error 16227 (Standby store has replicated transactions not present on the active) is one indication of trapped transactions. You can verify the number of trapped transactions by checking the number of records in replicated tables on each database during the manual recovery process. For example, enter a statement similar to the following:

SELECT COUNT(*) FROM reptable;

When there are trapped transactions, perform these tasks for recovery:

1. Use the ttRepStateSet built-in procedure to change the state on the standby database to 'ACTIVE'.

2. Destroy the old active database.

3. Use ttRepAdmin -duplicate to create a new standby database from the new active database, which has all of the transactions. See "Duplicating a database".

Failures in bidirectional distributed workload schemes

You can distribute the workload over multiple bidirectionally replicated databases, each of which serves as both master and subscriber. When recovering a master/subscriber database, the log on the failed database may present problems when you restart replication. See "Bidirectional distributed workload scheme".

If a database in a distributed workload scheme fails and work is shifted to a surviving database, the information in the surviving database becomes more current than that in the failed database. If replication is restarted at the failed system before the log failure threshold has been reached on the surviving database, then both databases attempt to update one another with the contents of their transaction logs. In this case, the older updates in the transaction log on the failed database may overwrite more recent data on the surviving system.

There are two ways to recover in such a situation:

- If the timestamp conflict resolution rules described in Chapter 13, "Resolving Replication Conflicts" are sufficient to guarantee consistency for your application, then you can restart the failed system and allow the updates from the failed database to propagate to the surviving database. The conflict resolution rules prevent more recent updates from being overwritten.

- Re-create the failed database, as described in "Recovering a failed database". If the database must be re-created, the updates in the log on the failed database that were not received by the surviving database cannot be identified or restored. In the case of several surviving databases, you must select which of the surviving databases is to be used to re-create the failed database. It is possible that at the time the failed database is re-created, the selected surviving database may not have received all updates from the other surviving databases. This results in diverging databases. The only way to prevent this situation is to re-create the other surviving databases from the selected surviving database.

Network failures

In the event of a temporary network failure, you do not need to perform any specific action to continue replication. The replication agents that were in communication attempt to reconnect every few seconds. If the agents reconnect before the master database runs out of log space, the replication protocol makes sure they do not miss or repeat any replication updates. If the network is unavailable for a longer period and the log failure threshold has been exceeded for the master log, you need to recover the subscriber as described in "Recovering a failed database".

Failures involving sequences

After a network link failure, if replication is allowed to recover by replaying queued logs, you do not need to take any action.

However, if the failed host was down for a significant amount of time, you must use the ttRepAdmin -duplicate command to repopulate the database on the failed host with transactions from the surviving host, as sequences are not rolled back during failure recovery. In this case, the ttRepAdmin -duplicate command copies the sequence definitions from one database to the other.

Recovering a failed database

If the databases are configured in a bidirectional replication scheme, a failed master database is automatically brought up to date from the subscriber. See "Automatic catch-up of a failed master database". Automatic catch-up also applies to recovery of master databases in active standby pairs.

If a restarted database cannot be recovered from its master's transaction log so that it is consistent with the other databases in the replicated system, you must re-create the database from one of its replication peers. Use command line utilities or the TimesTen Utility C functions. See "Recovering a failed database from the command line" and "Recovering a failed database from a C program".

Note:
It is not necessary to re-create the DSN for the failed database.

In the event of a subscriber failure, if any tables are configured with a return service, commits on those tables in the master database are blocked until the return service timeout period expires. To avoid this, you can establish a return service failure and recovery policy in your replication scheme, as described in "Managing return service timeout errors and replication state changes". If you are using the RETURN RECEIPT service, an alternative is to use ALTER REPLICATION and set the NO RETURN attribute to disable return receipt until the subscriber is restored and caught up. Then you can submit another ALTER REPLICATION statement to reestablish RETURN RECEIPT.

Recovering a failed database from the command line

If the databases are fully replicated, you can use the ttDestroy utility to remove the failed database from memory and ttRepAdmin -duplicate to re-create it from a surviving database. If the database contains any cache groups, you must also use the -keepCG option of ttRepAdmin. See "Duplicating a database".

Example 15-2 Recovering a failed database

To recover a failed database, subscriberds, from a master named masterds on host system1, enter:

> ttdestroy /tmp/subscriberds

> ttrepadmin -dsn subscriberds -duplicate -from masterds -host "system1" -uid ttuser

You are prompted for the password of ttuser.

Note:
ttRepAdmin -duplicate is supported only between identical and patch TimesTen releases. The major and minor release numbers must be the same.

After re-creating the database with ttRepAdmin -duplicate, the first connection to the database reloads it into memory. To improve performance when duplicating large databases, you can avoid the reload step by using the ttRepAdmin -ramload option to keep the database in memory after the duplicate operation.

Example 15-3 Keeping a database in memory when recovering it

To recover a failed database, subscriberds, from a master named masterds on host system1, and to keep the database in memory and restart replication after the duplicate operation, enter:

> ttdestroy /tmp/subscriberds

> ttrepadmin -dsn subscriberds -duplicate -ramload -from masterds -host "system1"
-uid ttuser -setmasterrepstart

You are prompted for the password of ttuser.

Note:
After duplicating a database with the ttRepAdmin -duplicate -ramLoad options, the RAM Policy for the database is manual until explicitly reset by ttAdmin -ramPolicy or the ttRamPolicy function.

Recovering a failed database from a C program

You can use the C functions provided in the TimesTen utility library to recover a failed database programmatically.

If the databases are fully replicated, you can use ttDestroyDataStore function to remove the failed database and the ttRepDuplicateEx function to re-create it from a surviving database.

Example 15-4 Recovering and starting a failed database

To recover and start a failed database, named subscriberds on host system2, from a master, named masterds on host system1, enter:

int          rc;
ttutilhandle utilhandle;
ttrepduplicateexarg arg;
memset( &arg, 0, sizeof( arg ) );
arg.size = sizeof( ttrepduplicateexarg );
arg.flags = tt_repdup_repstart | tt_repdup_ramload;
arg.uid=ttuser;
arg.pwd=ttuser;
arg.localhost = "system2";
rc = ttdestroydatastore( utilhandle, "subscriberds", 30 );
rc = ttrepduplicateex( utilhandle, "dsn=subscriberds",
"masterds", "system1", &arg );

In this example, the timeout for the ttDestroyDataStore operation is 30 seconds. The last parameter of the ttRepDuplicateEx function is an argument structure containing two flags:

- TT_REPDUP_RESTART to set the subscriberds database to the start state after the duplicate operation is completed

- TT_REPDUP_RAMLOAD to set the RAM policy to manual and keep the database in memory

Note:
When the TT_REPDUP_RAMLOAD flag is used with ttRepDuplicateEx, the RAM policy for the duplicate database is manual until explicitly reset by the ttRamPolicy function or ttAdmin -ramPolicy.

See "TimesTen Utility API" in Oracle TimesTen In-Memory Database C Developer's Guide for the complete list of the functions provided in the TimesTen C language utility library.

Recovering nondurable databases

If your database is configured with the TRANSMIT NONDURABLE option in a bidirectional configuration, you do not need to take any action to recover a failed master database. See "Automatic catch-up of a failed master database".

For other types of configurations, if the master database configured with the TRANSMIT NONDURABLE option fails, you must use ttRepAdmin-duplicate or ttRepDuplicateEx to re-create the master database from the most current subscriber database. If the application attempts to reconnect to the master database without first performing the duplicate operation, the replication agent recovers the database, but any attempt to connect results in an error that advises you to perform the duplicate operation. To avoid this error, the application must reconnect with the ForceConnect first connection attribute set to 1.

Writing a failure recovery script

Upon detecting a failure, the cluster manager should invoke a script that effectively executes the procedure shown by the pseudocode in Example 15-5.

Example 15-5 Failure recovery pseudocode

Detect problem {
if (Master == unavailable) {
FailedDataDatabase = Master
FailedDSN = Master_DSN
SurvivorDatabase = Subscriber
switch users to SurvivorDatabase
}
else {
FailedDatabase = Subscriber
FailedDSN = Subscriber_DSN
SurvivorDatabase = Master
}
}
Fix problem....
If (Problem resolved) {
Get state for FailedDatabase
if (state == "failed") {
ttDestroy FailedDatabase
ttRepAdmin -dsn FailedDSN -duplicate
-from SurvivorDatabase -host SurvivorHost
-setMasterRepStart
-uid ttuser
-pwd ttuser
}
else {
ttAdmin -repStart FailedDSN
}
while (backlog != 0) {
wait
}
}

Switch users back to Master.

This applies to either the master or subscriber databases. If the master fails, you may lose some transactions.

A TimesTen Configuration Attributes for Oracle Clusterware

The attributes defined in this chapter are used to set up TimesTen active standby pairs that are managed by Oracle Clusterware. These attributes are specified in the cluster.oracle.ini file. The ttCWAdmin utility creates and administers active standby pairs based on the information in the cluster.oracle.ini file.

List of attributes

This section lists the TimesTen configuration attributes for Oracle Clusterware in these tables:

- Table A-1, "Required attributes"

- Table A-2, "Conditionally required attributes"

- Table A-3, "Optional attributes"

Table A-1 Required attributes

Name

Description

Default

MasterHosts

Lists host names that may contain master databases in an active standby pair scheme.

None

Table A-2 Conditionally required attributes

Name

Description

Default

AppCheckCmd

Command line for checking the status of a TimesTen application that is managed by Oracle Clusterware.

None

AppName

The name of a TimesTen application that is managed by Oracle Clusterware.

None

AppStartCmd

Command line for starting a TimesTen application that is managed by Oracle Clusterware.

None

AppStopCmd

Command line for stopping a TimesTen application that is managed by Oracle Clusterware.

None

AppType

The database to which the application should link.

None

CacheConnect

Specifies whether the active standby pair replicates cache groups.

N

GridPort

Lists the port numbers used by the cache grid agents for the active database and the standby database in an active standby pair that is a cache grid member.

None

MasterVIP

A list of two virtual IP addresses that can be associated with the master databases.

None

RemoteSubscriberHosts

A list of subscriber hosts that are not part of the cluster.

None

RepBackupDir

The directory to which the active database is backed up.

None

SubscriberHosts

List of host names that can contain subscriber databases.

None

SubscriberVIP

The list of virtual IP addresses that can be associated with subscriber databases.

None

VIPInterface

The name of the public network adapter that is to be used for virtual IP addresses on each host.

None

VIPNetMask

The netmask of the virtual IP addresses.

None

Table A-3 Optional attributes

Name

Description

Default

AppFailoverDelay

The number of seconds that the Oracle Clusterware resource that monitors the application waits after a failure is detected before performing a failover.

0

AppFailureInterval

The interval in seconds before which Oracle Clusterware stops a TimesTen application if the application has exceeded the number of failures specified by the Oracle Clusterware FAILURE_THRESHOLD resource attribute.

60

AppFailureThreshold

The number of consecutive Oracle Clusterware resource failures that Oracle Clusterware tolerates for the action script for an application within an interval equal to 10 * AppScriptTimeout. The default is 2.

2

AppRestartAttempts

The number of times that Oracle Clusterware attempts to restart the TimesTen application on the current host before moving the application.

100

AppScriptTimeout

The number of seconds the TimesTen application container waits for the action scripts to complete for a specific application.

60

AppUptimeThreshold

The number of seconds that a TimesTen application must be up before Oracle Clusterware considers the application to be stable.

If the application fails within this threshold, the failure is considered a failure to start properly, and the application is restarted on another host. If the application is active past this threshold, it is considered stable. If it fails after being stable, the application is restarted on the same host.

600

AutoRecover

Specifies whether an active database should be automatically recovered from a backup if both master databases fail.

No

ClusterType

Defaults to Active. This is the only valid value for TimesTen.

Active

DatabaseFailoverDelay

The number of seconds that Oracle Clusterware waits before migrating a database to a new host after a failure.

60

FailureThreshold

The number of consecutive failures of resources managed by Oracle Clusterware that are tolerated within 10 seconds before the active standby pair is considered failed and a new active standby pair is created on spare hosts using the automated backup.

2

GridIPConf

Identifies what IP addresses to use for grid:

- Private: This is the default value that is recommended for TimesTen. Use private IP addresses as configured in the Oracle Clusterware cluster configuration.

- Public: Use public IP addresses as configured in the Oracle Clusterware cluster configuration.

Private

MasterStoreAttribute

A list of all desired replication scheme STORE attributes on master databases.

None

RepBackupPeriod

The number of seconds between each backup of the active database.

0 (disabled)

RepDDL

A SQL construct of the active standby pair scheme.

None

RepFullBackupCycle

The number times an incremental backup occurs between full backups.

5

ReturnServiceAttribute

The return service attribute of the active standby pair scheme.

None

SubscriberStoreAttribute

The list of all desired replication scheme STORE attributes for the subscriber database.

None

TimesTenScriptTimeout

The number of seconds that Oracle Clusterware waits for the monitor process to start before assuming a failure.

1209600 seconds, or 14 days

Required attributes

These attributes must be present for each DSN in the cluster.oracle.ini file. They have no default values.

The required attributes are listed in Table A-1, "Required attributes" and described in detail in this section.

MasterHosts

This attribute lists the host names that can contain master databases in the active standby pair. The first host listed has the active master database and the second host has the standby master database when the cluster is initially started. The following are exceptions to this designated order:

- If there are already active and standby master databases on specific nodes when the cluster is stopped, then the active and standby master databases remain on those hosts when the cluster is restarted.

- If the cluster is started and the only existing database is on a host that is not listed first in MasterHosts, then that host is to be configured with the active master database. The first host listed for MasterHosts is to be the standby master database.

You can specify more than two hosts as master hosts for advanced availablity. See "Configuring advanced availability" for details.

If you have only two master hosts configured, you should not define any virtual IP addresses. If more than two master hosts are listed, you should configure virtual IP addresses for internal TimesTen processes to manage replication in the situation of an unrecoverable failure of one of the hosts on which an active or standby database resides. See "Configuring advanced availability" for details.

Setting

Set MasterHosts as follows:

How the attribute is represented

Setting

MasterHosts

A comma-separated list of host names. The first host listed becomes the initial active master in the active standby pair. The second host listed becomes the initial standby master in the active standby pair.
The hosts defined must be different than the hosts defined for the SubscriberHosts attribute.

Conditionally required attributes

These attributes may be required depending on the desired Oracle Clusterware configuration. They have no default values. The conditionally required attributes are listed in Table A-2, "Conditionally required attributes" and described in detail in this section.

AppCheckCmd

This attribute specifies the full command line for executing a user-supplied script or program that checks the status of the TimesTen application specified by AppName. It must include the full path name of the executable. If there are spaces in the path name, enclose the path name in double quotes.

The command should be written to return 0 when the application is running and a nonzero number when the application is not running. When Oracle Clusterware detects a nonzero value, it takes action to recover the failed application.

Setting

Set AppCheckCmd as follows:

How the attribute is represented

Setting

AppCheckCmd

A string representing the command line for executing an application that checks the status of the application specified by AppName.

Examples

AppCheckCmd=/mycluster/reader/app_check.sh check

AppFailureInterval

This attribute sets the interval in seconds before which Oracle Clusterware stops a TimesTen application if the application has exceeded the number of failures specified by the Oracle Clusterware FAILURE_THRESHOLD resource attribute. If the value is zero, then failure tracking is disabled.

For more information about the Oracle Clusterware FAILURE_THRESHOLD resource attribute, see Oracle Clusterware Administration and Deployment Guide.

Setting

Set AppFailureInterval as follows:

How the attribute is represented

Setting

AppFailureInterval

The number of seconds in the interval before Oracle Clusterware stops an application. The default is 60. For example:
AppFailureInterval=120

AppName

This attribute specifies the name of a TimesTen application managed by Oracle Clusterware. Oracle Clusterware uses the application name to name the corresponding resource. Any description of an application in the cluster.oracle.ini file must begin with this attribute.

Setting

Set AppName as follows:

How the attribute is represented

Setting

AppName

A string representing the name of the application. For example, testApp.

AppRestartAttempts

This attribute specifies the number of times that Oracle Clusterware attempts to restart the TimesTen application on the current host before moving the application to another host.

Setting

Set AppRestartAttempts as follows:

How the attribute is represented

Setting

AppRestartAttempts

The number of restart attempts. The default is 100. For example:

AppRestartAttempts=30

AppStartCmd

This attribute specifies the command line that starts the TimesTen application specified by AppName. It must include the full path name of the executable. If there are spaces in the path name, enclose the path name in double quotes.

Setting

Set AppStartCmd as follows:

How the attribute is represented

Setting

AppStartCmd

A string that represents the command line for starting the application specified by AppName.

Examples

AppCheckCmd=/mycluster/reader/app_start.sh start

AppStopCmd

This attribute specifies the command line that stops the TimesTen application specified by AppName. It must include the full path name of the executable. If there are spaces in the path name, enclose the path name in double quotes.

Setting

Set AppStopCmd as follows:

How the attribute is represented

Setting

AppStopCmd

A string that represents the command line for stopping the application specified by AppName.

Examples

AppCheckCmd=/mycluster/reader/app_stop.sh stop

AppType

This attribute determines the hosts on which the TimesTen application should start.

Setting

Set AppType as follows:

How the attribute is represented

Setting

AppType

Active - The application starts on the active database of an active standby pair.
Standby - The application starts on the standby database of an active standby pair. If the standby database fails, applications linked to it migrate to the active database until a new standby database is available.

DualMaster - The application starts on both the active host and the standby host. The failure of the application on the active host causes the active database and all other applications on the host to fail over to the standby host.

Subscriber - The application starts on all subscriber databases.

Subscriber[index]- The application starts on a subscriber database. The subscriber host used is the host occupying position index in either the SubscriberHosts attribute or the SubscriberVIP attribute, depending on whether virtual IP addresses are used. For a single subscriber, use Subscriber[1]. If no index is specified, TimesTen assumes that the application links to all subscribers.

AppUptimeThreshold

This attribute specifies the value for the Oracle Clusterware UPTIME_THRESHOLD resource attribute.The value represents the number of seconds that a TimesTen application must be up before Oracle Clusterware considers the application to be stable.

For more information about UPTIME_THRESHOLD, see Oracle Clusterware Administration and Deployment Guide.

How the attribute is represented

Setting

AppUptimeThreshold

Number of seconds. The default is 600. For example:

AppUptimeThreshold=60

CacheConnect

If the active standby pair replicates cache groups, set this attribute to Y. If you specify Y, Oracle Clusterware assumes that TimesTen is connected to an Oracle database and prompts for the Oracle database password.

Setting

Set CacheConnect as follows:

How the attribute is represented

Setting

CacheConnect

A value of Y (yes) or N (no). Default is N.

GridPort

This attribute lists the port numbers used by the cache grid agents for the active database and the standby database in an active standby pair that is a cache grid member. The port numbers are separated by a comma. This is a mandatory parameter when global cache groups are present.

Setting

Set GridPort as follows

How the attribute is represented

Setting

GridPort

Two port numbers separated by a comma. For example:
GridPort=16101,16102

MasterVIP

This attribute defines two virtual IP (VIP) addresses associated with the two master hosts that are used by the active standby pair. If you configure more than two master hosts for advanced availability, you must also define two VIP addresses. However, these VIP addresses are used solely by internal TimesTen processes for managing the active standby pair in the case of an unrecoverable error on one of the master hosts. Use of these VIP addresses by any user or application can result in an error. See "Configuring advanced availability" for details.

Setting

Set MasterVIP as follows:

How the attribute is represented

Setting

MasterVIP

A comma-separated list of two virtual IP addresses to the master hosts.

RemoteSubscriberHosts

This attribute contains a list of subscriber hosts that are part of the active standby pair replication scheme but are not managed by Oracle Clusterware.

Setting

Set RemoteSubscriberHosts as follows:

How the attribute is represented

Setting

RemoteSubscriberHosts

A comma-separated list of subscriber hosts that are not managed by Oracle Clusterware.

RepBackupDir

This attribute indicates the directory where the backup of the active database is stored. This must be a directory in a shared file system that every node in the cluster can access. This attribute is required only if RepBackupPeriod is set to a value other than 0.

The directory must be shared by all hosts in the cluster. The shared storage must be NFS or OCFS (Oracle Cluster File System).

If you want to enable backup, install OCFS on the shared storage during the Oracle Clusterware installation process. You can use this shared storage for backup for an active standby pair.

See "Recovering from permanent failure of both master nodes" and "Failure and recovery for active standby pair grid members" for restrictions on backups.

Setting

Set RepBackupDir as follows:

How the attribute is represented

Setting

RepbackupDir

Full path name to the replication backup directory.

SubscriberHosts

Lists the host names that can contain subscriber databases. If the active standby pair is configured with subscribers, this attribute is required. It has no default value. You should have at least as many host names listed as there are subscribers defined.

If you are using advanced availability for your subscribers, define additional hosts that can be instantiated to take the place of any subscriber host that may encounter an unrecoverable error. Also, when using advanced availability, configure VIP addresses for every current subscriber in use. For example, if you have three subscribers and two additional hosts that can be used for advanced availability, you should have three VIP addresses defined. See SubscriberVIP for more information.

Setting

Set SubscriberHosts as follows:

How the attribute is represented

Setting

SubscriberHosts

A comma-separated list of host names.
The hosts defined must be different than the hosts defined for the MasterHosts attribute.

If not using advanced availability, the order of the hosts defined determines which application with an AppType of Subscriber[index] is attached to the subscriber database on a specific host. Also, the number of subscriber hosts specified is the number of subscribers that are part of the active standby pair. A subscriber is brought up on every subscriber host.

When using advanced availability, the first hosts listed are used for the subscriber hosts. The latter hosts defined are used for advanced availability.

SubscriberVIP

This attribute configures a list of the virtual IP (VIP) addresses associated with subscriber hosts that are used for advanced availability. When you configure more hosts than there are subscribers (for advanced availability), you must also define VIP addresses (one for each subscriber). However, these VIP addresses are used solely by internal TimesTen processes for managing replication in the case of an unrecoverable error on one of the subscriber hosts. Use of these VIP addresses by any user or application can result in an error. See "Configuring advanced availability" for details.

Setting

Set SubscriberVIP as follows:

How the attribute is represented

Setting

SubscriberVIP

One or more virtual IP addresses. You should define the same number of VIP addresses as the number of subscribers.
The order of subscriber virtual IP addresses is used to determine which application with an AppType of Subscriber[index] is attached to the database for a specific subscriber.

VIPInterface

This attribute is the name of the public network adapter used for virtual IP addresses on each host. This attribute is required if you intend to use virtual IP addresses.

Setting

Set VIPInterface as follows:

How the attribute is represented

Setting

VIPInterface

A string representing a network adapter.

VIPNetMask

This attribute is the netmask of the virtual IP addresses. This attribute is required if you intend to use virtual IP addresses.

Setting

Set VIPNetMask as follows:

How the attribute is represented

Setting

VIPNetMask

An IP netmask.

Optional attributes

These attributes are optional and have no default values. The optional attributes are listed in Table A-3, "Optional attributes" and described in detail in this section.

AppFailoverDelay

This attribute specifies the number of seconds that the process that is monitoring the application waits after a failure is detected before performing a failover. The default is 0.

Setting

Set AppFailoverDelay as follows:

How the attribute is represented

Setting

AppFailoverDelay

An integer representing the number of seconds that the process that is monitoring the application waits after a failure is detected before performing a failover. The default is 0.

AppFailureThreshold

This attribute specifies the number of consecutive failures that Oracle Clusterware tolerates for the action script for an application within an interval equal to 10 * AppScriptTimeout. The default is 2.

Setting

Set AppFailureThreshold as follows:

How the attribute is represented

Setting

AppFailureThreshold

An integer indicating the number of consecutive failures that Oracle Clusterware tolerates for the action script for an application. The default is 2.

AppScriptTimeout

This attribute indicates the number of seconds that the TimesTen application monitor process waits for the start action script and the stop action script to complete for a specific application. The check action script has a nonconfigurable timeout of five seconds and is not affected by this attribute.

Setting

Set AppScriptTimeout as follows:

How the attribute is represented

Setting

AppScriptTimeout

An integer representing the number of seconds the TimesTen application container waits for start and stop action scripts to complete for a specific application. The default is 60.

AutoRecover

Specifies whether Oracle Clusterware automatically recovers the active database from the backup in the case of a failure of both masters.

If recovery is not automated (AutoRecover=N), the database can be recovered using the ttCWAdmin -restore command.

You cannot use AutoRecover if you are using cache groups in your configuration or if a cache grid is configured.

Setting

Set AutoRecover as follows:

How the attribute is represented

Setting

AutoRecover

Y - Oracle Clusterware automatically recovers the active database from the backup if both masters fail.
N - In the case of the failure of both masters, you must recover manually. This is the default.

DatabaseFailoverDelay

This attributes specifies the number of seconds that Oracle Clusterware waits before migrating a database to a new host after a failure. Oracle Clusterware does not relocate a database if the database comes up during the delay period. This is applicable when advanced availability is configured. The default is 60 seconds.

Setting

Set DatabaseFailoverDelay as follows:

How the attribute is represented

Setting

DatabaseFailoverDelay

An integer representing the number of seconds that Oracle Clusterware waits before migrating a database to a new host after a failure. The default is 60.

FailureThreshold

This attribute specifies the number of consecutive failures of resources managed by Oracle Clusterware that are tolerated within 10 seconds before the active standby pair is considered failed and a new active standby pair is created on spare hosts using the automated backup. A spare node is only an option when using virtual IP addresses.

Oracle Clusterware tries to perform a duplicate for the active standby pair when a single failure occurs; it tries to perform a restoration if more than a single failure occurs.

This value is ignored for basic availability, since a spare node is only configured when at least one virtual IP address is configured, or is ignored when RepBackupPeriod is set to 0 when using advanced availability, which does include the configuration of at least one virtual IP address.

Note:
TimesTen tolerates only one failure of a backup resource, regardless of the setting for this attribute.

Setting

Set FailureThreshold as follows:

How the attribute is represented

Setting

FailureThreshold

An integer representing the number of consecutive failures of resources managed by Oracle Clusterware that are tolerated within 10 seconds before the active standby pair is considered failed and a new active standby pair is created on spare hosts using the automated backup. The default is 2.

MasterStoreAttribute

This attribute indicates the desired replication scheme STORE attributes for the master databases. The STORE attributes apply to both the active and standby databases. For more information on STORE attributes, see "Setting STORE attributes".

This attribute is not required when RepDDL is configured.

If this attribute is not set, the STORE attributes take their default values.

Setting

Set MasterStoreAttribute as follows:

How the attribute is represented

Setting

MasterStoreAttribute

The desired replication scheme STORE attributes for the master databases. For example: PORT 20000 TIMEOUT 60.

RepBackupPeriod

This attribute indicates the number of seconds between each backup of the active database. If this attribute is set to a value greater than 0, you must also specify a backup directory by setting RepBackupDir.

See "Recovering from permanent failure of both master nodes" and "Failure and recovery for active standby pair grid members" for restrictions on backups.

Setting

Set RepBackupPeriod as follows:

How the attribute is represented

Setting

RepBackupPeriod

An integer indicating the number of seconds between each backup of the active database. A value of 0 disables the backup process. The default is 0.

RepDDL

This attribute represents the SQL statement that creates the active standby pair. Use this attribute only in special circumstances. For example, you must specify RepDDL if you need to exclude tables and sequences from the active standby pair.

If RepDDL is set, do not set these attributes:

- ReturnServiceAttribute

- MasterStoreAttribute

- SubscriberStoreAttribute

Replace the database file name prefix in the SQL statement with the <DSN> macro. Use the <MASTERHOST[1]>, <MASTERHOST[2]> and <SUBSCRIBERHOST[n]> macros instead of the host names.

There is no default value for RepDDL.

This example sets RepDDL for two master databases:

RepDDL=CREATE ACTIVE STANDBY PAIR <DSN> ON <MASTERHOST[1]>, <DSN> ON <MASTERHOST[2]>

See "Using the RepDDL attribute" for additional examples.

You do not usually need to set the ROUTE clause in RepDDL because the transmitter of the replication agent automatically obtains the private and public network interfaces that Oracle Clusterware uses. However, if hosts have network connectivity for replication schemes that are not managed by Oracle Clusterware, then RepDDL needs to include the ROUTE clause.

If this attribute is used, each STORE clause must be followed by the pseudo host names such as:

- ActiveHost

- ActiveVIP

- StandbyHost

- StandbyVIP

- SubscriberHost

- SubscriberVIP

Setting

Set RepDDL as follows:

How the attribute is represented

Setting

RepDDL

Creates an active standby pair by issuing a CREATE ACTIVE STANDBY PAIR statement. There is no default value.

RepFullBackupCycle

This attribute specifies the number of incremental backups between full backups. The number of incremental backups depends on the capacity of the shared storage.

Setting this attribute can impact performance. There is a trade-off between the storage capacity and the time consumption for backup. An incremental backup can be performed much faster than a full backup. However, storage consumption increases until a full backup is performed.

See "Recovering from permanent failure of both master nodes" and "Failure and recovery for active standby pair grid members" for restrictions on backups.

Setting

Set RepFullBackupCycle as follows:

How the attribute is represented

Setting

RepFullBackupCycle

An integer value representing the number of incremental backups to perform between full backups. The default is 5.

ReturnServiceAttribute

This attribute specifies the return service for the active standby replication scheme. See "Using a return service".

If no value is specified for this attribute, the active standby pair is configured with no return service.

Setting

Set ReturnServiceAttribute as follows:

How the attribute is represented

Setting

ReturnServiceAttribute

The type of return service. For example: RETURN RECEIPT. There is no default value.

SubscriberStoreAttribute

This attribute indicates the replication scheme STORE attributes of subscriber databases. The STORE attributes apply to all subscribers. For more information on STORE attributes, see "Setting STORE attributes".

This attribute is not required when RepDDL is present.

If this attribute is not set, the STORE attributes take their default values.

Setting

Set SubscriberStoreAttribute as follows:

How the attribute is represented

Setting

SubscriberStoreAttribute

The list of STORE attributes and their values for the subscriber databases.
For example: PORT 20000 TIMEOUT 60.

TimesTenScriptTimeout

This attribute specifies the number of seconds that Oracle Clusterware waits for the monitor process to start before assuming a failure.

Oracle TimesTen recommends setting a value of several hours because the action script may take a long time to duplicate the active database. The default is 1209600 seconds (14 days).

Setting

Set TimesTenScriptTimeout as follows:

How the attribute is represented

Setting

TimesTenScriptTimeout

An integer representing the number of seconds that Oracle Clusterware waits for the monitor process to start before assuming a failure. The default is 1209600 seconds (14 days).

Index
A  B  C  D  E  F  G  H  I  L  M  N  O  P  R  S  T  U  V  W

A

active master

change to standby, 5.6

detecting dual active masters, 5.7

dual failure recovery, 5.4

active standby pair, 3.13, 7.1

add or drop table column, 7.1

adding host to cluster, 8.6.3.1

adding or dropping a subscriber, 7.2

adding or dropping cache groups, 7.2

adding sequences and cache groups, 7.2

altering, 7.2

changing PORT or TIMEOUT connection attributes, 7.2

configuring network interfaces, 3.10, 4.3.3

create or drop index, 7.1

create or drop synonym, 7.1

defined, 1.5.1

detecting dual active masters, 5.7

disaster recovery, 6.11

dropping sequences and cache groups, 7.2

DSN, 3.4

examples of altering, 7.2.1

failback, 5.2.2, 6.5.2

overview, 1.5.1

recover after dual master failure, 5.4

recovering active master, 5.2

replicating a global AWT cache group, 6.3

replicating a local read-only cache group, 6.2

replicating materialized views, 3.14

replicating sequences, 3.15

restrictions, 3.3

return service, 3.8, 4.1

reverse roles, 5.6

setting up, 5.1

states, 3.1

SUBSCRIBER clause, 3.7

subscriber failure, 5.5

active standby pair with cache groups

dual failure recovery, 6.7

recovering active master, 6.5

subscriber failure, 6.8

ADD ELEMENT clause

DATASTORE, 10.1.3

ADMIN privilege, 3.6, 9.2 aging

replication, 1.9

ALTER ELEMENT clause, 10.1.1 ALTER REPLICATION state

using, 10.1

ALTER REPLICATION statement, 9.5.3 ALTER TABLE statement

and replication, 10.2

ALTER USER statement, 10.1 AppCheckCmd Clusterware attribute, A.1 AppFailoverDelay Clusterware attribute, A.1 AppFailureInterval attribute

Oracle Clusterware, A.1

AppFailureThreshold Clusterware attribute, A.1 application failover

Oracle Clusterware, 8.2.5

AppName Clusterware attribute, A.1 AppRestartAttempts attribute

Oracle Clusterware, A.1

AppScriptTimeout Clusterware attribute, A.1 AppStartCmd Clusterware attribute, A.1 AppStopCmd Clusterware attribute, A.1 AppType Clusterware attribute, A.1 AppUptimeThreshold attribute

Oracle Clusterware, A.1

asynchronous writethrough cache group

propagating to Oracle database, 1.6.2

replication, 1.6.1

attributes, connection

required, 11.1.2

autocommit mode

RETURN RECEIPT BY REQUEST, 4.1.3

RETURN TWOSAFE, 4.1.4

RETURN TWOSAFE BY REQUEST, 4.1.5

automatic catch-up, 15.2.3 automatic client failover, 3.11, 8.1 AutoRecover Clusterware attribute, A.1 AWT cache group

propagating to Oracle Database, 1.6.2

replicating, 1.6.1, 6.3

AWT cache groups

parallel threads, 11.1.3.1

B

bidirectional general workload

syntax example, 9.11.6

update conflicts, 9.11.6

bidirectional replication scheme

recovery, 9.1.1

return twosafe service, 4.1.4

bidirectional split workload

syntax example, 9.11.5

bookmarks in log, 11.1.4.3, 12.5

C

cache

changing cache administration user name or password, 6.4

changing user name or password, 6.4

cache grid

active standby pairs, 6.3

add cache group with Oracle Clusterware, 8.4.3.1

creating a cluster, 8.4.1

drop cache group with Oracle Clusterware, 8.4.3.2

managing with Oracle Clusterware, 8.4

recovery with Oracle Clusterware, 8.4.2, 8.5.5.2

schema changes with Oracle Clusterware, 8.4.3

cache groups

replicating, 1.6

replicating a global AWT cache group, 6.3

replicating a read-only cache group, 6.2

replicating a user managed cache group, 6.1

CacheAWTParallelism connection attribute, 11.1.3.1 CacheConnect Clusterware attribute, 8.2.3, A.1 catch-up feature

replication, 15.2.3

CHECK CONFLICTS clause

examples, 13.3.2

in CREATE REPLICATION statement, 9.6

classic replication

high availability, 9.1

classic replication scheme, 9 client failover, 8.1

automatic client failover, 3.11

cluster

virtual IP addresses, 8.1

cluster agent, 8.3.2 cluster manager

role, 9.1.1

cluster status, 8.7 cluster.oracle.ini file, 8.1

advanced availability, 8.2.2

advanced availability, one subscriber, 8.2.2

and sys.odbc.ini file, 8.2

application failover, 8.2.5, 8.2.5

attribute descriptions, A

automatic recovery from failure of both master nodes, 8.2.6

basic availability, 8.2.1

basic availability, one subscriber, 8.2.1

cache grid, 8.2.4

cache groups, 8.2.3

examples, 8.2

excluding tables, cache groups and sequences, 8.2.7

location, 8.2

manual recovery from failure of both master nodes, 8.2.6

specify route, 8.2.7

Clusterware, see Oracle Clusterware columns

compressed, 3.5, 9.3

COMPRESS TRAFFIC clause

in CREATE ACTIVE STANDBY PAIR statement, 4.2.3

in CREATE REPLICATION statement, 4.2.3

compression

table columns, 3.5, 9.3

conflict

reporting, 13.4

XML Document Type Definition, 13.5

resolution, 13.1

update rules, 13.2

types, 13.1 CONFLICT REPORTING clause

in CREATE REPLICATION statement, 4.2.7, 4.2.7

copying a database

privileges, 3.2

copying a master database, 11.2 CREATE ACTIVE STANDBY PAIR statement, 5.1, 6.2

syntax, 3.6

create or drop table, 7.1 CREATE REPLICATION statement, 9.5.3

defining DATASTORE element, 9.5.1

defining table element, 9.5.2

use of, 9.2

CREATE USER statement, 10.1 crsctl command

check crs command, 8.3.1

verify Oracle Clusterware status, 8.3.1

crsTT directories, 8.1.2

D

data source name, 9.2.2

data types

size limits, 3.5, 9.3

database

connection failure, 4.2.6

duplicating, 11.2

failed, 4.2.6

ForceConnect connection attribute, 15.2.3

name, 9.2.2

objects

excluding from active standby pair, 3.12

temporary, 3.3, 9.5.1 DatabaseCharacterSet data store attribute, 11.1.2 DatabaseFailoverDelay Clusterware attribute, A.1 databases

establishing, 11.1.1

managing logs, 11.1.4

recovering, 9.1.1

required connection attributes for replication, 11.1.2

setting state, 11.6

DATASTORE element, 9.5, 9.5.1

adding to replication scheme, 10.1.3

and materialized views, 9.5.5

and nonmaterialized views, 9.5.5

DDL statements

replication, 7.1.1

DDLReplicationAction connection attribute, Preface, 7.1.1 DDLReplicationLevel connection attribute, Preface, 7.1.1 default column values

changing, 10.2

DISABLE RETURN clause

in CREATE ACTIVE STANDBY PAIR statement, 4.2.1.1.4

DISABLE RETURN policy, 4.2.1.1.4

active standby pair, 4.2.1.1.4, 4.2.1.1.6

disaster recovery

active standby pair with AWT cache group, 6.11

disaster recovery subscriber

Oracle Clusterware, 8.3.13

distributed workload configuration

recovery issues, 9.1.1

distributed workload replication, 1.5.2.2.2 DNS server

Windows, 4.3.4.2

DROP REPLICATION statement, 2.2.6, 10.4 DROP USER statement, 10.1 dropping replication scheme, 2.2.6, 10.4 DSN

creating, 2.2.1, 11.1.1

define for active standby pair, 3.4

defining, 9.2.2

DualMaster

Oracle Clusterware, 8.2.5

duplicating a database

privileges, 3.2

with cache groups, 3.2

duplicating a master database, 11.2 DURABLE COMMIT clause

in CREATE ACTIVE STANDBY PAIR statement, 4.2.1.1.6

in CREATE REPLICATION statement, 4.2.1.1.6

DURABLE COMMIT policy, 4.2.1.1.6

E

element

DATASTORE, 9.5.1

defined, 1.1

ELEMENT descriptions, 9.5 EXACT

table definition, 4.2.2

example

replicating tables to different subscribers, 9.11.3

EXCLUDE clause

in CREATE ACTIVE STANDBY PAIR statement, 3.12

EXCLUDE SEQUENCE clause

in ALTER REPLICATION statement, 10.1.3.2

in CREATE REPLICATION statement, 9.5.1

EXCLUDE TABLE clause

in ALTER REPLICATION statement, 10.1.3.2

in CREATE REPLICATION statement, 9.5.1

F

failback, 5.2.2

active standby pair, 6.5.2

failed database

connecting to, 4.2.6

failed state

replication, 11.6

failover, 3.11 failover and recovery

issues, 9.1.1

FAILTHRESHOLD attribute, 15.2.1 FAILTHRESHOLD clause

active standby pair, 4.2.1.1.3

altering, 10.1.13

example, 9.11.2

in CREATE ACTIVE STANDBY PAIR statement, 4.2.6, 4.2.6

in CREATE REPLICATION statement, 4.2.1.1.3, 4.2.1.1.3, 4.2.6

subscriber failures, 15.2.1

failure

return service, 4.2.1.1.2

subscriber, 5.5, 15.2.1

failure recovery script, 15.5 failure threshold

description, 11.1.4.3

displaying, 12.4.1

example, 9.11.2

subscriber failures, 15.2.1

FailureThreshold Clusterware attribute, A.1 ForceConnect connection attribute, 15.2.3, 15.2.3, 15.4 foreign keys

active standby pair replication, 3.13

classic replication, 9.5.3

ON DELETE CASCADE

classic replication, 9.5.3

replication, 1.8 full replication, 1.5.2.1 full store name

active standby pair, 3.7

G

general workload

syntax example, 9.11.6

GRANT statement, 10.1 GridPort Clusterware attribute, 8.2.4, A.1

H

high availability

classic replication

design, 9.1

host

IP address, 4.3

IP addresses, 4.3.4

local, 4.3

host name

identifying, 4.3.4, 9.5.1

hostname command, 9.5.1

I

INCLUDE clause

in CREATE ACTIVE STANDBY PAIR statement, 3.12

INCLUDE SEQUENCE clause

in ALTER REPLICATION statement, 10.1.3.1

in CREATE REPLICATION statement, 9.5.1

INCLUDE TABLE clause

in ALTER REPLICATION statement, 10.1.3.1

in CREATE REPLICATION statement, 9.5.1

IP addresses

replication, 4.3.4

L

LOB columns

size limit, 3.5, 9.3

LOCAL COMMIT ACTION clause

active standby pair, 4.2.1.1.7

LOCAL COMMIT ACTION policy, 4.2.1.1.7 log

locating bookmarks, 11.1.4.3, 12.5

management, 11.1.4

size and persistence, 11.1.4.1

threshold value, 11.1.4.3

log sequence number, 12.5 LogBufMB connection attribute, 11.1.4.3, 11.1.4.3 LogBufParallelism first connection attribute, 11.1.3.1, 11.1.3.2 LogFileSize connection attribute, 11.1.4.3 logging, 11.1.4.3 logs

setting the size, 11.1.4.3

LSN, 12.5

M

master catch-up, 15.2.3

master database

defined, 9.2.2

MasterHosts Clusterware attribute, A.1 MasterStoreAttribute Clusterware attribute, A.1 MasterVIP Clusterware attribute, A.1 materialized views

active standby pair, 3.14

replicating, 9.5.5

monitoring replication, 12

N

network

bandwidth, 4.3

configuration, 4.3

WAN environment, 4.3, 4.3.2

network configuration

interfaces, 4.3.3

replication, 4.3

Network Time Protocol, see NTP NO RETURN clause

in CREATE ACTIVE STANDBY PAIR statement, 4.1.6

in CREATE REPLICATION statement, 4.1.6

NTP

clock management, 8.1.2

-x option, 8.1.2

NVARCHAR columns

size limit, 3.5, 9.3

NVARCHAR2 columns

size limit, 3.5, 9.3

O

ocrConfig option, 8.3.3

ON DELETE CASCADE

classic replication, 9.5.3

foreign keys

active standby pair, 3.13

ON DELETE CASCADE clause

replication, 1.8

Oracle Cluster Registry

configuring for TimesTen cluster, 8.3.3

Oracle Clusterware, 8

add cache group to cache grid, 8.4.3.1

add subscriber not managed by Oracle Clusterware, 8.6.5.3

adding active standby pair to cluster, 8.6.4.1

adding subscriber to active standby pair, 8.6.5.1

altering tables and cache groups, 8.6.6

AppFailureInterval attribute, A.1

application failure, A.1

AppRestartAttempts, A.1

AppType=DualMaster, 8.2.5

AppUptimeThreshold, A.1

AppUptimeThreshold attribute, A.1

automatic recovery, 8.2.6

automatic recovery from dual failure, 8.5.5.1

cache grid, 8.2.4

cache grid recovery, 8.4.2, 8.5.5.2

changing cache administration user name or password, 8.6.11

changing internal user name or password, 8.6.11

cluster.oracle.ini and sys.odbc.ini files, 8.2

creating a cluster of cache grid members, 8.4.1

creating or dropping tables and cache groups, 8.6.6

crsctl start command, 8.5.7

crsctl stop command, 8.5.7

crsTT directories, 8.1.2

drop cache group from cache grid, 8.4.3.2

failure of both master nodes, 8.2.6

failure of more than two master hosts, 8.5.6

forced switchover, 8.5.7

GridPort attribute, 8.2.4

host maintenance, 8.6.9

machine room maintenance, 8.6.10

manual recovery for advanced availability, 8.5.5.3

manual recovery for basic availability, 8.5.5.4

message log files, 8.7.2

moving a database to another host, 8.6.8

network maintenance, 8.6.9

RAM policy, 8.6.12

rebuild subscriber not managed by Oracle Clusterware, 8.6.5.4

recovery process, 8.5.1

recovery when RETURN TWOSAFE, 8.5.5.6

remote disaster recovery subscriber, 8.3.13

removing active standby pair from cluster, 8.6.4.2

removing host from cluster, 8.6.3.2

removing subscriber from active standby pair, 8.6.5.2

required privileges, 8.1.1

restricted commands, 8.1.3

rolling upgrade, 8.6.1

routing, 8.2.7

schema changes in cache grid, 8.4.3

status, 8.7

stopping the TimesTen daemon, 8.3.4

storage for backups, 8.2.6

subscriber not managed by Oracle Clusterware, 8.3.14

switching the active and the standby, 8.6.7

TimesTen advanced level, 8.1

TimesTen basic level, 8.1

TimesTen cluster agent, 8.3.4, 8.3.4

TimesTen daemon monitor, 8.3.4, 8.3.4

tmp directory, 8.1.2

ttDaemonAdmin, 8.3.4

upgrading TimesTen, 8.6.2

using RepDDL attribute, 8.2.7

using with cache grid, 8.4

virtual IP addresses, 8.1

Oracle Clusterware attributes

AppCheckCmd, A.1

AppFailoverDelay, A.1

AppFailureThreshold, A.1

AppName, A.1

AppScriptTimeout, A.1

AppStartCmd, A.1

AppStopCmd, A.1

AppType, A.1

AutoRecover, A.1

CacheConnect, A.1

conditional, A.1

DatabaseFailoverDelay, A.1

FailureThreshold, A.1

GridPort, A.1

MasterHosts, A.1

MasterStoreAttribute, A.1

MasterVIP, A.1

optional, A.1, A.1

RemoteSubscriberHosts, A.1

RepBackupDir, A.1

RepBackupPeriod, A.1

RepDDL, 8.2.7, A.1

RepFullBackupCycle, A.1

required, A.1, A.1

ReturnServiceAttribute, A.1

SubscriberHosts, A.1

SubscriberStoreAttribute, A.1

SubscriberVIP, A.1

TimesTenScriptTimeout, A.1

VIPInterface, A.1

VIPNetMask, A.1

owner

replication scheme, 9.2.1

P

parallel replication, 11.1.3

attributes, 11.1.2

automatic, 11.1.3, 11.1.3.1

AWT, 11.1.3.1

DDL statements, 11.1.3

DML statements, 11.1.3

partitions

in a table, 4.2.2

PassThrough connection attribute

and RETURN TWOSAFE, 4.1.4

and RETURN TWOSAFE BY REQUEST, 4.1.5

pause state

replication, 11.6

performance

altered tables, 14.2

evaluation tool, 12.8

logging attributes, 11.1.4.3

replication, 14, 14.2

replication throughput, 14.3

PL/SQL object

replicating in an active standby pair, 7.1.3

PL/SQL objects

replicating, 10.1.2

PORT assignment

active standby pair, 4.2.4

PORT attribute

CREATE ACTIVE STANDBY PAIR statement, 4.2.4

CREATE REPLICATION statement, 4.2.4

ports

dynamic, 4.2.4

static, 4.2.4

privilege

create a replication scheme, 9.2

create an active standby pair, 3.6

propagation

example, 9.11.4

PROPAGATOR clause

example, 9.11.4

propagator database

defined, 9.2.2

R

RAM policy

Oracle Clusterware, 8.6.12

read-only cache group

replicating, 1.6.3

ReceiverThreads first connection attribute, 11.1.2 recovering failed databases, 9.1.1 recovery

return service, 4.2.1.1.2

RecoveryThreads attribute, 14.3 RELAXED

table checking, 14.2

table definition, 4.2.2, 4.2.2

RemoteSubscriberHosts Clusterware attribute, A.1 RepBackupDir Clusterware attribute, A.1 RepBackupPeriod Clusterware attribute, A.1 RepDDL Clusterware attribute, 8.2.7, A.1

example, 8.2.7

RepFullBackupCycle Clusterware attribute, A.1 replicated tables

requirements, 9.3

replicating over a network, 4.3 replication

across releases, 11.4

aging, 1.9

and ttAdmin, 11.5

AWT cache group, 1.6.1

cache groups, 1.6

classic, 1.5.2

bidirectional replication scheme, 1.5.2.2

direct, 1.5.2.3

distributed workload configuration, 1.5.2.2.2

foreign keys, 9.5.3

full replication, 1.5.2.1

propagation, 1.5.2.3

selective replication, 1.5.2.1

split workload, 1.5.2.2.1

unidirectional replication, 1.5.2.2

configuring timestamp comparison, 13.3 conflict reporting, 13.4 conflict resolution, 13.1 controlling, 11.6, 11.6 DDL statements, 7.1.1 described, 1.1 design decisions, 9.1 element, 1.1, 9.5 failed state, 11.6 FAILTHRESHOLD clause in CREATE ACTIVE STANDBY PAIR statement, 4.2.1.1.3 FAILTHRESHOLD clause in CREATE REPLICATION statement, 4.2.1.1.3 foreign keys, 1.8

active standby pair, 3.13

ON DELETE CASCADE, 3.13

gauging performance, 12.5 host IP addresses, 4.3.4 monitoring, 12 of materialized views, 9.5.5 of sequences, 9.5.4 ON DELETE CASCADE clause, 1.8 over a network, 1.5.2.3 parallelism, see parallel replication pause state, 11.6 performance, 14.2 propagator database

definition, 1.5.2.3

relaxed checking, 4.2.2 restart policy, 11.5 return receipt, 1.4.2 start state, 11.6 starting, 11.5 state, 11.6 stop state, 11.6 stopped

return services policy, 4.2.1.1.3

stopping, 11.5, 11.5 tables with different definitions, 4.2.2 timestamp column maintenance, 13.3.2.1 unidirectional, 1.5.2.2 WAN environment, 4.3.2 replication agent

defined, 1.3

starting, 2.2.4, 11.5

stopping, 2.2.6, 11.5

replication daemon, see "replication agent" replication performance, 14.3 replication scheme

active standby pair, 1.5.1

applying to DSNs, 9.12

configuring, 9.1

defining, 9.2

examples, 9.11

for cache groups, 1.6

naming, 9.2.1

owner, 9.2.1

types, 1.5

ReplicationApplyOrdering connection attribute, 11.1.3.1 ReplicationApplyOrdering data store attribute, 11.1.2, 11.1.3.1 ReplicationParallelism connection attribute, 11.1.3.1 ReplicationParallelism data store attribute, 11.1.2, 11.1.3.1, 11.1.3.2 repschemes

ttIsql command, 12.4.1

resource

defined, 8.1

restart policy, 11.5 restrictions

active standby pairs, 3.3

RESUME RETURN clause

in CREATE ACTIVE STANDBY PAIR statement, 4.2.1.1.5

RESUME RETURN policy, 4.2.1.1.5

active standby pair, 4.2.1.1.5, 4.2.1.1.5

return receipt

definition, 1.4

RETURN RECEIPT BY REQUEST clause

example, 9.11.2

in CREATE ACTIVE STANDBY PAIR statement, 4.1.3

in CREATE REPLICATION statement, 4.1.3

RETURN RECEIPT clause

active standby pair, 4.1.2

CREATE REPLICATION statement, 4.1.2

example, 9.11.1, 9.11.2, 9.11.2

RETURN RECEIPT failure policy

report settings, 12.4.1

return receipt replication, 1.4.2 RETURN RECEPT timeout errors, 1.4.2 return service

active standby pair, 3.8, 4.1

blocking

disabling, 4.2.1.1.2

CREATE REPLICATION statement, 4.1 failure policy, 4.2.1.1, 4.2.1.1.2 in CREATE REPLICATION statement, 9.8 performance and recovery tradeoffs, 9.1.2 recovery policy, 4.2.1.1.2 timeout errors, 4.2.1.1 return services

policy

when replication stopped, 4.2.1.1.3

RETURN SERVICES clause

in CREATE ACTIVE STANDBY PAIR statement, 4.2.1.1.3

return twosafe

bidirectional replication scheme, 4.1.4, 4.1.4

definition, 1.4

Oracle Clusterware recovery, 8.5.5.6

RETURN TWOSAFE BY REQUEST clause

in CREATE ACTIVE STANDBY PAIR statement, 4.1.5

in CREATE REPLICATION statement, 4.1.5

RETURN TWOSAFE clause

in CREATE ACTIVE STANDBY PAIR statement, 4.1.4

in CREATE REPLICATION statement, 4.1.4

ReturnServiceAttribute Clusterware attribute, A.1

example, 8.5.5.6

REVOKE statement, 10.1 roles

reverse, 5.6

ROUTE clause

CREATE ACTIVE STANDBY PAIR statement, 4.3.3

CREATE REPLICATION statement, 4.3.3

in CREATE ACTIVE STANDBY PAIR statement, 3.10

in replication scheme, 9.10

S

selective replication, 1.5.2.1

SEQUENCE element, 9.5

sequences

adding to replication scheme, 10.1.1

changing element name, 10.1.7

dropping from replication scheme, 10.1.4

replicating, 1.7, 9.5.4

replicating in an active standby pair, 3.15

split workload, 1.5.2.2.1

replication scheme

recovery, 9.1.1

syntax example, 9.11.5 SQLGetInfo function

checking database state, 4.2.6

monitoring subscriber, 15.2.1

standby master

change to active, 5.6

dual failure recovery, 5.4

recover from failure, 5.3, 6.6

start state

replication, 11.6

starting the replication agent, 2.2.4, 11.5 status

cluster, 8.7

Oracle Clusterware, 8.7

stop state

replication, 11.6

stopping the replication agent, 2.2.6, 11.5 STORE attributes

in CREATE ACTIVE STANDBY PAIR statement, 3.9, 4.2

in CREATE REPLICATION statement, 4.2, 9.9

subscriber

adding to replication scheme, 10.1.5

displaying status, 12.3

dropping from replication scheme, 10.1.6

transaction log accumulation, 12.3

SUBSCRIBER clause

and return service, 9.8

in CREATE ACTIVE STANDBY PAIR statement, 3.7

return service, 4.1

subscriber database

defined, 9.2.2

subscriber failure, 5.5, 15.2.1

active standby pair with cache groups, 6.8

SubscriberHosts Clusterware attribute, A.1 subscribers

maximum number, 9.11.2

SubscriberStoreAttribute Clusterware attribute, A.1 SubscriberVIP Clusterware attribute, A.1

T

table

adding to replication scheme, 10.1.1

alter

performance, 14.2

changing element name, 10.1.7 definitions, 4.2.2 dropping from replication scheme, 10.1.4 excluding from database, 10.1.3.2 including in database, 10.1.3.1 partitioned, 4.2.2 relaxed checking, 4.2.2, 14.2 TABLE DEFINITION CHECKING clause

examples, 4.2.2

TABLE element, 9.5, 9.5.2 table requirements

active standby pairs, 3.5

replication schemes, 9.3

tables

altering and replication, 10.2

threshold log setting, 11.1.4.3 time

clock management

NTP, 8.1.2

timeout

return service for an active standby pair, 4.2.1

timestamp

from operating system, 13.2

timestamp column maintenance

by user, 13.3.2.2

system, 13.3.2.1

timestamp comparison

configuring, 13.3

local transactions, 13.2.1

TimesTen cluster agent, 8.3.2, 8.3.4, 8.3.4 TimesTen daemon monitor, 8.3.4, 8.3.4 TimesTenScriptTimeout Clusterware attribute, A.1 track

parallel replication, 11.1.3.2.1, 11.1.3.3

transaction log

threshold, 4.2.6, 4.2.6

failed state, 4.2.6

transaction logs

analyze, 12.8

TRANSMIT DURABLE clause

in CREATE REPLICATION statement, 9.7

TRANSMIT NONDURABLE clause

and recovery, 15.4

in CREATE REPLICATION statement, 9.7

trapped transaction, 15.2.3.1 TRUNCATE TABLE statement, 10.3 truncating a replicated table, 10.3 TT_VARCHAR columns

size limit, 3.5, 9.3

ttAdmin utility

-ramPolicy option, 15.3.1, 15.3.2

-repPolicy option, 11.5

-repStart option, 11.5, 11.5

-repStop option, 11.5

ttCkpt built-in procedure, 11.1.4.2 ttCkptBlocking built-in procedure, 11.1.4.2 ttCRSActiveService process, 8.3.10 ttCRSAgent process, 8.3.4, 8.3.4 ttcrsagent.options file, 8.3.2, 8.3.2 ttCRSDaemon process, 8.3.4, 8.3.4 ttCRSMaster process, 8.3.10 ttCRSsubservice process, 8.3.10 ttCWAdmin

-beginAlterSchema option, 8.4.3, 8.6.6.1, 8.6.6.1

ttCWAdmin -beginAlterSchema command, 8.4.3, 8.6.6.1, 8.6.6.1 ttCWAdmin -endAlterSchema command, 8.4.3, 8.6.6.1 ttCWAdmin utility, 8.1, 8.2

-endAlterSchema option, 8.4.3, 8.6.6.1

ocrConfig option, 8.3.3

-relocate option, 8.6.8

required privileges, 8.1.1

-status option, 8.7

-switch option, 8.6.7

ttcwerrors.log file, 8.7.2 ttcwmsg.log file, 8.7.2 ttDestroy utility, 15.3.1 ttDestroyDataStore built-in procedure, 15.3.2 ttDurableCommit built-in procedure, 4.2.1.1.1 ttIsql utility

-f option, 9.12

ttMigrate utility

relaxedUpgrade option, 14.2, 14.2

ttRepAdmin utility

-bookmark option, 12.5.3

displaying subscriber information, 12.3.1

-duplicate option, 4.2.2, 9.7, 11.2, 15.2.3, 15.3.1, 15.3.1, 15.4

privileges for -duplicate options, 3.2

-ramLoad option, 15.3.1, 15.3.1

-receiver -list options, 12.3.1

-self -list options, 12.2.1

-showconfig option, 12.4.2

-state option, 11.6

ttRepDuplicate built-in procedure, 15.3.2 ttRepDuplicateEx C function

privileges, 3.2

ttReplicationStatus built-in procedure, 12.3.2 ttRepReturnTransitionTrap SNMP trap, 4.2.1.1.4 ttRepStart built-in procedure, 10.1, 11.5 ttRepStop built-in procedure, 10.1, 11.5 ttRepSubscriberStateSet built-in procedure, 11.6 ttRepSubscriberWait built-in procedure

replicating sequences, 3.15, 9.5.4

ttRepSyncGet built-in procedure, 4.1.3, 4.1.5, 4.1.5 ttRepSyncSet built-in procedure, 4.1.3, 4.1.3, 4.1.5, 4.2.1, 4.2.1, 4.2.1.1.7

different return services, 9.11.2

LOCAL ACTION policy, 4.2.1.1.7

RETURN RECEIPT BY REQUEST, 4.1.3

setting return service timeout, 4.2.1

ttRepSyncSubscriberStatus built-in procedure, 4.2.1.1, 12.7.1

DISABLE RETURN clause, 4.2.1.1.4

ttRepXactStatus built-in procedure, 4.1, 4.2.1.1.7, 4.2.1.1.7, 12.7.2 ttRepXactTokenGet built-in procedure, 12.7.2 ttXactLog utility

logAnalyze command, 12.8

TypeMode data store attribute, 11.1.2

U

unidirectional replication, 1.5.2.2

update conflicts

example, 9.11.6

syntax example, 9.11.6

V

VARBINARY columns

size limit, 3.5, 3.5, 9.3, 9.3

VARCHAR2 columns

size limit, 3.5, 9.3

views

active standby pair, 3.14

VIPInterface Clusterware attribute, A.1 VIPNetMask Clusterware attribute, A.1 virtual IP address

Oracle Clusterware, 8.1

W

WAN environment, 4.3.2

replication, 4.3

WINS server

Windows, 4.3.4.2

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