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4 Database Considerations

This chapter describes what to consider as you configure database connections for Oracle Fusion Middleware in a high availability setup. It also describes the benefits of using Oracle Real Application Clusters (Oracle RAC), a commonly-deployed database high availability solution.

Most Fusion Middleware components use a database as the persistent store for their data. When you use an Oracle database, you can configure it in a variety of highly available configurations. (For more information on Oracle database options, see the Oracle Database High Availability Overview.)

This chapter includes the following topics:

4.1 About Oracle Real Application Clusters

A cluster comprises multiple interconnected computers or servers that appear as if they are one server to end users and applications. Oracle RAC enables you to cluster an Oracle database, providing a highly scalable and highly available database for Oracle Fusion Middleware.

All Oracle Fusion Middleware components deployed to Oracle WebLogic Server support Oracle RAC.

Every Oracle RAC instance in the cluster has equal access and authority, therefore, node and instance failure may affect performance, but doesn't result in downtime; the database service is available or can be made available on surviving server instances.

Table 4-1 outlines tasks and corresponding sources of information for setting up Oracle RAC.

Table 4-1 Roadmap for Setting up Oracle RAC

Task/Topic More Information

About Oracle RAC

"Introduction to Oracle RAC" in the Oracle Real Application Clusters Administration and Deployment Guide

Installing Oracle RAC

Oracle Real Application Clusters Administration and Deployment Guide

Managing Oracle RAC

"Overview of Managing Oracle RAC Environments" in Oracle Real Application Clusters Administration and Deployment Guide

Configuring and tuning GridLink and multi data sources

Oracle Fusion Middleware Configuring and Managing JDBC Data Sources for Oracle WebLogic Server

Configuring Single Client Access Name (SCAN) URLs. (To specify the host and port for the TNS and ONS listeners in the WebLogic console.)

"SCAN Addresses" in the guide Oracle Fusion Middleware Configuring and Managing JDBC Data Sources for Oracle WebLogic Server.


4.2 About RAC Database Connections and Failover

To establish connection pools, Oracle Fusion Middleware supports Active GridLink data sources and multi data sources for the Oracle RAC back end for both XA and non-XA JDBC drivers. See Section 4.2.1, "About XA Transactions" for more information about XA transactions. These data sources also support load balancing across Oracle RAC nodes.

When an Oracle RAC node or instance fails, Oracle WebLogic Server or the Oracle Thin JDBC driver redirect session requests to another node in the cluster. There is no failover of existing connections. However, new connection requests from the application are managed using existing connections in the Oracle WebLogic pool or by new connections to the working Oracle RAC instance.

When the database is the transaction manager, in-flight transactions typically roll back.

When WebLogic Server is the transaction manager, in-flight transactions fail over; they are driven to completion or rolled back based on the transaction state when failure occurs.

4.2.1 About XA Transactions

XA transaction support enables multiple resources (such as databases, application servers, message queues, transactional caches) to be accessed within the same transaction. A non-XA transaction always involves just one resource.

An XA transaction involves a coordinating transaction manager with one or more databases, or other resources such as JMS, all involved in a single global transaction.

Java EE uses the terms JTA transaction, XA transaction, user transaction, and global transaction interchangeably to refer to a single global transaction. This type of transaction may include operations on multiple different XA- capable or non-XA resources and even different resource types. A JTA transaction is always associated with the current thread and may be passed from server to server as one application calls another. A common example of an XA transaction is one that includes both a WebLogic JMS operation and a JDBC (database) operation.

4.3 About Data Sources

A data source is an abstraction that application components use to obtain connections to a relational database. Specific connection information, such as the URL or user name and password, are set on a data source object as properties and do not need to be explicitly defined in an application's code. This abstraction allows applications to be built in a portable manner, because the application is not tied to a specific back-end database. The database can change without affecting the application code.

Oracle provides Active GridLink data sources and multi data sources to support high availability, load balancing, and failover of database connections. Oracle recommends the following data source types depending on the Oracle RAC Database version you have:

  • If you use Oracle RAC database version 11g Release 2 and later, use Active GridLink data sources.

  • If you use an Oracle RAC database version earlier than 11g Release 2 or a non-Oracle database, use multi data sources.

Note:

Oracle recommends using the Active GridLink data sources with Oracle RAC database for maximum availability. For versions of Oracle RAC databases where Active GridLink data sources are not supported, Oracle recommends using multi data sources for high availability.

See the following topics for more information on these data source types:

4.3.1 Active GridLink Data Sources

An Active GridLink data source provides connectivity between WebLogic Server and an Oracle database service, which may include multiple Oracle RAC clusters. An Active GridLink data source includes the features of generic data sources plus the following support for Oracle RAC:

  • Uses the Oracle Notification Service (ONS) to respond to state changes in an Oracle RAC.

  • Responds to Fast Application Notification (FAN) events to provide Fast Connection Failover (FCF), Runtime Connection Load-Balancing, and RAC instance graceful shutdown. FAN is a notification mechanism that Oracle RAC uses to quickly alert applications about configuration and workload.

  • Provides Affinities (or XA Affinity) policies to ensure all database operations for a session are directed to the same instance of a RAC cluster for optimal performance.

See "Using Active GridLink Data Sources" in the Oracle Fusion Middleware Configuring and Managing JDBC Data Sources for Oracle WebLogic Server guide for more information on the following topics:

4.3.2 Multi Data Sources

A multi data source is an abstraction around a group of data sources that provides load balancing or failover processing at the time of connection requests, between the data sources associated with the multi data source. Multi data sources support load balancing for both XA and non-XA data sources.

A multi data source provides an ordered list of data sources to use to satisfy connection requests. Normally, every connection request to this kind of multi data source is served by the first data source in the list. If a database connection test fails and the connection cannot be replaced, or if the data source is suspended, a connection is sought sequentially from the next data source on the list."

Multi data sources are bound to the JNDI tree or local application context just like regular data sources. Applications look up a multi data source on the JNDI tree or in the local application context (java:comp/env) just as they do for data sources, and then request a database connection. The multi data source determines which data source to use to satisfy the request depending on the algorithm selected in the multi data source configuration: load balancing or failover.

See Also:

For more information about configuring Multi Data Sources with Oracle RAC, see "Using Multi Data Sources with Oracle RAC" in the guide Oracle Fusion Middleware Configuring and Managing JDBC Data Sources for Oracle WebLogic Server.

4.4 Configuring Active GridLink Data Sources with Oracle RAC

How you configure an Active GridLink data source depends on the Oracle component that you are working with and the domain you are creating.

This section describes how to configure component data sources as Active GridLink data sources for a RAC database during domain creation.

This topic includes the following sections:

See Also:

To create and configure Active GridLink data sources, see Using Active GridLink Data Sources in Oracle Fusion Middleware Configuring and Managing JDBC Data Sources for Oracle WebLogic Server.

4.4.1 Requirements

Verify that your system meets the following requirements before you configure component data sources as Active GridLink data sources to use with an Oracle RAC database:

  • You are using Oracle RAC database version 11g Release 2 or later.

  • You have run RCU to create component schemas.

  • You are using the Configuration Wizard to create or configure a domain and have arrived at the JDBC Component Schema screen where you select Component Datasources. Before you arrive at the JDBC Component Schema screen, you must select the option Configure Manually in the Database Configuration Type screen.

4.4.2 Configuring Component Data Sources as Active GridLink Data Sources

To configure component data sources as Active GridLink data sources:

  1. In the JDBC Component Schema screen, select one or more component schemas to configure GridLink data sources for.

  2. Select Convert to GridLink then select Next.

  3. In the GridLink Oracle RAC Component Schema screen, select one of the GridLink JDBC drivers.

  4. In the Service Name field, enter the service name of the database using lowercase characters. For example, mydb.example.com.

  5. In the Schema Owner field, enter the name of the database schema owner for the corresponding component.

  6. In the Schema Password field, enter the password for the database schema owner.

  7. In the Service Listener, Port, and Protocol field, enter the SCAN address and port for the RAC database being used. The protocol for Ethernet is TCP; for Infiniband it is SDP. Click Add to enter multiple listener addresses.

    You can identify the SCAN address by querying the appropriate parameter in the database using the TCP protocol:

    show parameter remote_listener
    
    
    
    NAME                   TYPE                 VALUE
    
    --------------------------------------------------------------------
    
    remote_listener        string              db-scan.example.com:1521
    
    
    

    You can also identify the SCAN address by using the srvctl config scan command. Use the command srvctl config scan_listener to identify the SCAN listener port.

  8. Select Enable FAN to receive and process FAN events. Enter one or more ONS daemon listen addresses and port information. Select Add to enter more entries.

    Note:

    Verify that the ONS daemon listen address(es) that you enter is valid. The address is not validated during the domain creation process.

    For the ONS host address, you can use the SCAN address for the Oracle RAC database and the ONS remote port as reported by the database:

    srvctl config nodeapps -s
    
    ONS exists: Local port 6100, remote port 6200, EM port 2016
    
  9. Select Enable SSL for SSL communication with ONS. Enter the Wallet File, which has the SSL certificates, and the Wallet Password.

  10. Select Next. Verify that all connections are successful.

Note:

See "Modifying the mdsDS Data Source URL" to use an Active GridLink data source with a customer-provided ADF application.

See Also:

For more information, see:

  • "JDBC Component Schema" in Oracle Fusion Middleware Creating WebLogic Domains Using the Configuration Wizard for information about the JDBC Component Schema screen.

  • "GridLink Oracle RAC Component Schema" in Oracle Fusion Middleware Creating WebLogic Domains Using the Configuration Wizard for information about configuring component schemas.

  • "Using Active GridLink Data Sources" in Administering JDBC Data Sources for Oracle WebLogic Server for information on GridLink RAC data sources.

4.4.3 Using Single Client Access Name (SCAN) Addresses for Hosts and Ports

Oracle recommends that you use Oracle Single Client Access Name (SCAN) addresses to specify the host and port for both the TNS listener and the ONS listener in the WebLogic console. You do not need to update an Active GridLink data source containing SCAN addresses if you add or remove Oracle RAC nodes. Contact your network administrator for appropriately configured SCAN URLs for your environment. See SCAN Addresses in the Oracle Fusion Middleware Configuring and Managing JDBC Data Sources for Oracle WebLogic Server guide.

4.5 Configuring Multi Data Sources

You can configure multi data sources using the following:

  • Oracle Fusion Middleware Configuration Wizard during WebLogic Server domain creation

  • Oracle WebLogic Server Administration Console

  • WLST Commands

This section includes the following topics:

4.5.1 Configuring Multi Data Sources with Oracle RAC

This section describes the requirements and procedure to configure multi data sources with Oracle RAC.

This section includes the following topics:

4.5.1.1 Requirements

Verify that your system meets the following requirements before you configure component data sources as multi data sources to use with an Oracle RAC database:

  • You are using an Oracle RAC database.

  • You have run RCU to create component schemas.

  • You are using the Configuration Wizard to create or configure a domain and have arrived at the JDBC Component Schema Screen where you select Component Schemas.

4.5.1.2 Configuring Component Data Sources as Multi Data Sources

To configure component data sources as multi data sources:

  1. In the Component Datasources screen, select one or more component schemas to configure Active GridLink data sources for.

  2. Select Convert to RAC multi data source then select Next.

  3. In the Oracle RAC Multi Data Source Component Schema screen, the JDBC driver Oracle's Driver (Thin) for RAC Service-Instance connections; Versions:10 and later.

  4. In the Service Name field, enter the database service name enter in lowercase, for example, mydb.example.com.

  5. In the Schema Owner field, enter the username of the database schema owner for the corresponding component. Typically this name is RCUprefix_component.

  6. In the Schema Password field, enter the password for the database schema owner.

  7. In the Host Name, Instance Name, and Port field, enter the RAC node hostname, database instance name, and port. Click Add to enter multiple listener addresses.

  8. Click Next.Verify that all connections are successful.

4.5.1.3 Modifying or Creating Multi Data Sources After Initial Configuration

The multi data sources have constituent data sources for each RAC instance providing the database service. Oracle recommends that you add an additional data source to the multi data source on the Fusion Middleware tier when you add an additional instance to the RAC back end.

When you migrate a database from a non-RAC to a RAC database, you must create an equivalent, new multi data source for each data source that is affected. The multi data source that you create must have constituent data sources for each RAC instance. The data source property values must be identical to the original single instance data source for the properties in Section 4.5.1. For example, if the single instance data source driver is oracle.jdbc.xa.client.OracleXADataSource, it must be oracle.jdbc.xa.client.OracleXADataSource for each constituent data source of the new multi data source.

For multi data sources that you create manually or modify after initial configuration, Oracle strongly recommends specific XA and non-XA data source property values for optimal high availability. Make changes only after careful consideration and testing if your environment requires that you do so.

The following tables describe XA and non-XA data source property values that Oracle recommends:

Table 4-2 Recommended Multi Data Source Configuration

Property Name Recommended Value

test-frequency-seconds

5

algorithm-type

Load-Balancing


For individual data sources, Oracle recommends the following for high availability environments. Oracle recommends that you set any other parameters according to application requirements.

Table 4-3 XA Data Source Configuration

Property Name Recommended Value

Driver

oracle.jdbc.xa.client.OracleXADataSource

Property command

<property>

<name>oracle.net.CONNECT_TIMEOUT</name>

<value>10000</value>

</property>

initial-capacity

0

connection-creation-retry-frequency-seconds

10

test-frequency-seconds

300

test-connections-on-reserve

true

test-table-name

SQL SELECT 1 FROM DUAL

seconds-to-trust-an-idle-pool-connection

0

global-transactions-protocol

TwoPhaseCommit

keep-xa-conn-till-tx-complete

true

xa-retry-duration-seconds

300

xa-retry-interval-seconds

60


Troubleshooting Warning Messages (Increasing Transaction Timeout for XA Data Sources)

If you see WARNING messages in the server logs that include the following exception, this message may indicate that the XA timeout value you have in your setup must be increased.

[ javax.transaction.SystemException: Timeout during commit processing

You can increase XA timeout for individual data sources when these warnings appear.

To increase the transaction timeout for the XA Data Sources setting, use the Administration Console:

  1. Access the data source configuration.

  2. Select the Transaction tab.

  3. Set the XA Transaction Timeout to a larger value, for example, 300.

  4. Select the Set XA Transaction Timeout checkbox. You must select this checkbox for the new XA transaction timeout value to take effect.

  5. Click Save.

Repeat this configuration for all individual data sources of an XA multi data source.

Table 4-4 Non-XA Data Source Configuration

Property Name Recommended Value

Driver

oracle.jdbc.OracleDriver

Property to set

<property>

<name>oracle.net.CONNECT_TIMEOUT</name>

<value>10000</value>

</property>

initial-capacity

0

connection-creation-retry-frequency-seconds

10

test-frequency-seconds

300

test-connections-on-reserve

true

test-table-name

SQL SELECT 1 FROM DUAL

seconds-to-trust-an-idle-pool-connection

0

global-transactions-protocol

None


4.5.2 Configuring Multi Data Sources for MDS Repositories

You can configure applications that use an MDS database-based repository for high availability Oracle database access. With this configuration, failure detection, recovery, and retry by MDS (and by the WebLogic infrastructure) result in application read-only MDS operations being protected from Oracle RAC database planned and unplanned downtimes.

Multi data sources are exposed as MDS repositories in the Fusion Middleware Control navigation tree. You can select these multi data sources when you customize the application deployment and use them with MDS WLST commands.

  • Configuring an application to retry read-only operations

    To configure an application to retry the connection, you can configure the RetryConnection attribute of the application's MDS AppConfig MBean. See the Oracle Fusion Middleware Administrator's Guide for more information.

  • Registering an MDS multi data source

    In addition to the steps in Section 4.5.1, "Configuring Multi Data Sources with Oracle RAC," consider the following:

    • The child data sources that constitute a multi data source used for an MDS repository must be configured as non-XA data sources.

    • The multi data source's name must have the prefix mds-. This ensures that the multi data source is recognized as an MDS repository that can be used for MDS management functionality through Fusion Middleware Control, WLST, and JDeveloper.

      Note:

      When an MDS data source is added as a child of a multi data source, this data source is no longer exposed as an MDS repository. For example, it does not appear under the Metadata Repositories folder in the Fusion Middleware Control navigation tree, you cannot perform MDS repository operations on it, and it does not appear in the list of selectable repositories during deployment.

  • Converting a data source to a multi data source

    There are two things to consider when you convert a data source to a multi data source to verify that the application is configured correctly:

    • To create a new multi data source with a new, unique name, redeploy the application and select this new multi data source as the MDS repository during deployment plan customization.

    • To avoid redeploying the application, you can delete the data source and recreate the new multi data source using the same name and jndi-name attributes.

Note:

See "Modifying the mdsDS Data Source URL" to use a multi data source with a customer-provided ADF application.