|Oracle® Real Application Clusters Administration and Deployment Guide
11g Release 2 (11.2)
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This chapter briefly describes database design and deployment techniques for Oracle Real Application Clusters (Oracle RAC) environments. It also describes considerations for high availability and provides general guidelines for various Oracle RAC deployments.
This chapter includes the following topics:
Many customers implement Oracle RAC to provide high availability for their Oracle Database applications. For true high availability, you must make the entire infrastructure of the application highly available. This requires detailed planning to ensure there are no single points of failure throughout the infrastructure. Even though Oracle RAC makes your database highly available, if a critical application becomes unavailable, then your business can be negatively affected. For example, if you choose to use the Lightweight Directory Access Protocol (LDAP) for authentication, then you must make the LDAP server highly available. If the database is up but the users cannot connect to the database because the LDAP server is not accessible, then the entire system appears to be down to your users.
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For mission critical systems, you must be able to perform failover and recovery, and your environment must be resilient to all types of failures. To reach these goals, start by defining service level requirements for your business. The requirements should include definitions of maximum transaction response time and recovery expectations for failures within the datacenter (such as for node failure) or for disaster recovery (if the entire data center fails). Typically, the service level objective is a target response time for work, regardless of failures. Determine the recovery time for each redundant component. Even though you may have hardware components that are running in an active/active mode, do not assume that if one component fails the other hardware components can remain operational while the faulty components are being repaired. Also, when components are running in active/passive mode, perform regular tests to validate the failover time. For example, recovery times for storage channels can take minutes. Ensure that the outage times are within your business' service level agreements, and where they are not, work with the hardware vendor to tune the configuration and settings.
When deploying mission critical systems, the testing should include functional testing, destructive testing, and performance testing. Destructive testing includes the injection of various faults in the system to test the recovery and to make sure it satisfies the service level requirements. Destructive testing also allows the creation of operational procedures for the production system.
To help you design and implement a mission critical or highly available system, Oracle provides a range of solutions for every organization regardless of size. Small workgroups and global enterprises alike are able to extend the reach of their critical business applications. With Oracle and the Internet, applications and their data are now reliably accessible everywhere, at any time. The Oracle Maximum Availability Architecture (MAA) is the Oracle best practices blueprint that is based on proven Oracle high availability technologies and recommendations. The goal of the MAA is to remove the complexity in designing an optimal high availability architecture.
Oracle Maximum Availability Architecture (MAA) Web site at
Applications can take advantage of many Oracle Database, Oracle Clusterware, and Oracle RAC features and capabilities to minimize or mask any failure in the Oracle RAC environment. For example, you can:
Remove TCP/IP timeout waits by using the VIP address to connect to the database.
Create detailed operational procedures and ensure you have the appropriate support contracts in place to match defined service levels for all components in the infrastructure.
Take advantage of the Oracle RAC Automatic Workload Management features such as connect time failover, Fast Connection Failover, Fast Application Notification, and the Load Balancing Advisory. See Chapter 5, "Introduction to Automatic Workload Management" for more details.
Place voting disks on separate volume groups to mitigate outages due to slow I/O throughput. To survive the failure of x voting devices, configure 2x + 1 mirrors.
Use Oracle Database Quality of Service Management (Oracle Database QoS Management) to monitor your system and detect performance bottlenecks
Place OCR with I/O service times in the order of 2 milliseconds (ms) or less.
Tune database recovery using the
FAST_START_MTTR_TARGET initialization parameter.
Use Oracle Automatic Storage Management (Oracle ASM) to manage database storage.
Ensure that strong change control procedures are in place.
Check the surrounding infrastructure for high availability and resiliency, such as LDAP, NIS, and DNS. These entities affect the availability of your Oracle RAC database. If possible, perform a local backup procedure routinely.
Use Oracle Enterprise Manager to administer your entire Oracle RAC environment, not just the Oracle RAC database. Use Oracle Enterprise Manager to create and modify services, and to start and stop the cluster database instances and the cluster database. See the Oracle Database 2 Day + Real Application Clusters Guide for more information using Oracle Enterprise Manager in an Oracle RAC environment.
Use Recovery Manager (RMAN) to back up, restore, and recover data files, control files, server parameter files (SPFILEs) and archived redo log files. You can use RMAN with a media manager to back up files to external storage. You can also configure parallelism when backing up or recovering Oracle RAC databases. In Oracle RAC, RMAN channels can be dynamically allocated across all of the Oracle RAC instances. Channel failover enables failed operations on one node to continue on another node. You can start RMAN from Oracle Enterprise Manager Backup Manager or from the command line. See Chapter 6, "Configuring Recovery Manager and Archiving" for more information about using RMAN.
If you use sequence numbers, then always use
CACHE with the
NOORDER option for optimal performance in sequence number generation. With the
CACHE option, however, you may have gaps in the sequence numbers. If your environment cannot tolerate sequence number gaps, then use the
NOCACHE option or consider pre-generating the sequence numbers. If your application requires sequence number ordering but can tolerate gaps, then use
ORDER to cache and order sequence numbers in Oracle RAC. If your application requires ordered sequence numbers without gaps, then use
ORDER combination has the most negative effect on performance compared to other caching and ordering combinations.
Note:If your environment cannot tolerate sequence number gaps, then consider pre-generating the sequence numbers or use the
If you use indexes, then consider alternatives, such as reverse key indexes to optimize index performance. Reverse key indexes are especially helpful if you have frequent inserts to one side of an index, such as indexes that are based on insert date.
Many people want to consolidate multiple applications in a single database or consolidate multiple databases in a single cluster. Oracle Clusterware and Oracle RAC support both types of consolidation.
Creating a cluster with a single pool of storage managed by Oracle ASM provides the infrastructure to manage multiple databases whether they are single instance databases or Oracle RAC databases.
With Oracle RAC databases, you can adjust the number of instances and which nodes run instances for a given database, based on workload requirements. Features such as cluster-managed services allow you to manage multiple workloads on a single database or across multiple databases.
It is important to properly manage the capacity in the cluster when adding work. The processes that manage the cluster—including processes both from Oracle Clusterware and the database—must be able to obtain CPU resources in a timely fashion and must be given higher priority in the system. Oracle Database Quality of Service Management (Oracle Database QoS Management) can assist consolidating multiple applications in a cluster or database by dynamically allocating CPU resources to meet performance objectives.
See Also:Oracle Database Quality of Service Management User's Guide for more information
Oracle recommends that the number of real time Global Cache Service Processes (LMSn) on a server is less than or equal to the number of processors. (Note that this is the number of recognized CPUs that includes cores. For example, a dual-core CPU is considered to be two CPUs.) It is important that you load test your system when adding instances on a node to ensure that you have enough capacity to support the workload.
If you are consolidating many small databases into a cluster, you may want to reduce the number of LMSn created by the Oracle RAC instance. By default, Oracle Database calculates the number of processes based on the number of CPUs it finds on the server. This calculation may result in more LMSn processes than is needed for the Oracle RAC instance. One LMS process may be sufficient for up to 4 CPUs.To reduce the number of LMSn processes, set the
GC_SERVER_PROCESSES initialization parameter minimally to a value of 1. Add a process for every four CPUs needed by the application. In general, it is better to have few busy LMSn processes. Oracle Database calculates the number of processes when the instance is started, and you must restart the instance if you want to change the value.
Oracle RAC provides concurrent, transactionally consistent access to a single copy of the data from multiple systems. It provides scalability beyond the capacity of a single server. If your application scales transparently on symmetric multiprocessing (SMP) servers, then it is realistic to expect the application to scale well on Oracle RAC, without the need to make changes to the application code.
Traditionally, when a database server runs out of capacity, it is replaced with a new larger server. As servers grow in capacity, they become more expensive. However, for Oracle RAC databases, you have alternatives for increasing the capacity:
You can maintain the investment in the current hardware and add a new server to the cluster (or create or add a new cluster) to increase the capacity.
Adding servers to a cluster with Oracle Clusterware and Oracle RAC does not require an outage. As soon as the new instance is started, the application can take advantage of the extra capacity.
All servers in the cluster must run the same operating system and same version of Oracle Database but the servers do not have to be exactly the same capacity. With Oracle RAC, you can build a cluster that fits your needs, whether the cluster is made up of servers where each server is a two-CPU commodity server or clusters where the servers have 32 or 64 CPUs in each server. The Oracle parallel execution feature allows a single SQL statement to be divided up into multiple processes, where each process completes a subset of work. In an Oracle RAC environment, you can define the parallel processes to run only on the instance where the user is connected or to run across multiple instances in the cluster.
This section briefly describes database design and deployment techniques for Oracle RAC environments. It also describes considerations for high availability and provides general guidelines for various Oracle RAC deployments.
Consider performing the following steps during the design and development of applications that you are deploying on an Oracle RAC database:
Tune the design and the application
Tune the memory and I/O
Tune the operating system
Note:If an application does not scale on an SMP system, then moving the application to an Oracle RAC database cannot improve performance.
Is transparent to the application
If you use hash partitioning for tables and indexes for OLTP environments, then you can greatly improve performance in your Oracle RAC database. Note that you cannot use index range scans on an index with hash partitioning.
This section describes considerations when deploying Oracle RAC databases. Oracle RAC database performance is not compromised if you do not employ these techniques. If you have an effective noncluster design, then your application will run well on an Oracle RAC database.
This section includes the following topics:
ASSM distributes instance workloads among each instance's subset of blocks for inserts. This improves Oracle RAC performance because it minimizes block transfers. To deploy automatic undo management in an Oracle RAC environment, each instance must have its own undo tablespace.
As a general rule, only use DDL statements for maintenance tasks and avoid executing DDL statements during peak system operation periods. In most systems, the amount of new object creation and other DDL statements should be limited. Just as in noncluster Oracle databases, excessive object creation and deletion can increase performance overhead.
If you add nodes to your Oracle RAC database environment, then you may need to increase the size of the
SYSAUX tablespace. Conversely, if you remove nodes from your cluster database, then you may be able to reduce the size of your
See Also:Your platform-specific Oracle RAC installation guide for guidelines about sizing the
SYSAUXtablespace for multiple instances
To ensure this, create multiple Oracle Distributed Transaction Processing (DTP) services, with one or more on each Oracle RAC instance. Each DTP service is a singleton service that is available on one and only one Oracle RAC instance. All access to the database server for distributed transaction processing must be done by way of the DTP services. Ensure that all of the branches of a single global distributed transaction use the same DTP service. In other words, a network connection descriptor, such as a TNS name, a JDBC URL, and so on, must use a DTP service to support distributed transaction processing.
"Services and Distributed Transaction Processing in Oracle RAC" for more details about enabling services and distributed transactions
Oracle Database Advanced Application Developer's Guide for more information about distributed transactions in Oracle RAC
High availability in the event of failures
The high availability features of Oracle Database and Oracle RAC can re-distribute and load balance workloads to surviving instances without interrupting processing. Oracle RAC also provides excellent scalability so that if you add or replace a node, then Oracle Database re-masters resources and re-distributes processing loads.
To accommodate the frequently changing workloads of online transaction processing systems, Oracle RAC remains flexible and dynamic despite changes in system load and system availability. Oracle RAC addresses a wide range of service levels that, for example, fluctuate due to:
Varying user demands
Peak scalability issues like trading storms (bursts of high volumes of transactions)
Varying availability of system resources
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Oracle RAC is ideal for data warehouse applications because it augments the noncluster benefits of Oracle Database. Oracle RAC does this by maximizing the processing available on all of the nodes that belong to an Oracle RAC database to provide speed-up for data warehouse systems.
The query optimizer considers parallel execution when determining the optimal execution plans. The default cost model for the query optimizer is CPU+I/O and the cost unit is time. In Oracle RAC, the query optimizer dynamically computes intelligent defaults for parallelism based on the number of processors in the nodes of the cluster. An evaluation of the costs of alternative access paths, table scans versus indexed access, for example, takes into account the degree of parallelism (DOP) available for the operation. This results in Oracle Database selecting the execution plans that are optimized for your Oracle RAC configuration.
Oracle Database's parallel execution feature uses multiple processes to run SQL statements on one or more CPUs. Parallel execution is available on both noncluster Oracle databases and Oracle RAC databases.
Oracle RAC takes full advantage of parallel execution by distributing parallel processing across all available instances. The number of processes that can participate in parallel operations depends on the DOP assigned to each table or index.
Oracle Database 11g release 2 (11.2) enables Oracle RAC nodes to share the wallet. This eliminates the need to manually copy and synchronize the wallet across all nodes. Oracle recommends that you create the wallet on a shared file system. This allows all instances to access the same shared wallet.
Oracle RAC uses wallets in the following ways:
Any wallet operation, like opening or closing the wallet, performed on any one Oracle RAC instance is applicable for all other Oracle RAC instances. This means that when you open and close the wallet for one instance, then it opens and closes the wallet for all Oracle RAC instances.
When using a shared file system, ensure that the
ENCRYPTION_WALLET_LOCATION parameter for all Oracle RAC instances points to the same shared wallet location. The security administrator must also ensure security of the shared wallet by assigning appropriate directory permissions.
Note:If Oracle Automatic Storage Management Cluster File System (Oracle ACFS) is available for your operating system, then Oracle recommends that you store the wallet in Oracle ACFS. If you do not have Oracle ACFS in Oracle ASM, then use the Oracle ASM Configuration Assistant (ASMCA) to create it. You must add the mount point to the
sqlnet.orafile in each instance, as follows:
ENCRYPTION_WALLET_LOCATION= (SOURCE = (METHOD = FILE) (METHOD_DATA = (DIRECTORY = /opt/oracle/acfsmounts/data_wallet)))
This file system is mounted automatically when the instances start. Opening and closing the wallet, as well as commands to set or rekey and rotate the TDE master encryption key, are synchronized between all nodes.
A master key rekey performed on one instance is applicable for all instances. When a new Oracle RAC node comes up, it is aware of the current wallet open or close status.
Do not issue any wallet
close commands while setting up or changing the master key.
Deployments where shared storage does not exist for the wallet require that each Oracle RAC node maintain a local wallet. After you create and provision a wallet on a single node, you must copy the wallet and make it available to all of the other nodes, as follows:
For systems using Transparent Data Encryption with encrypted wallets, you can use any standard file transport protocol, though Oracle recommends using a secured file transport.
For systems using Transparent Data Encryption with obfuscated wallets, file transport through a secured channel is recommended.
To specify the directory in which the wallet must reside, set the or
ENCRYPTION_WALLET_LOCATION parameter in the
sqlnet.ora file. The local copies of the wallet need not be synchronized for the duration of Transparent Data Encryption usage until the server key is re-keyed though the
ALTER SYSTEM SET KEY SQL statement. Each time you issue the
ALTER SYSTEM SET KEY statement on a database instance, you must again copy the wallet residing on that node and make it available to all of the other nodes. Then, you must close and reopen the wallet on each of the nodes. To avoid unnecessary administrative overhead, reserve re-keying for exceptional cases where you believe that the server master key may have been compromised and that not re-keying it could cause a serious security problem.
See Also:Oracle Database Advanced Security Administrator's Guide for more information about creating and provisioning a wallet
By default, all installations of Windows Server 2003 Service Pack 1 and higher enable the Windows Firewall to block virtually all TCP network ports to incoming connections. As a result, any Oracle products that listen for incoming connections on a TCP port will not receive any of those connection requests, and the clients making those connections will report errors.
Depending upon which Oracle products you install and how they are used, you may need to perform additional Windows post-installation configuration tasks so that the Firewall products are functional on Windows Server 2003.
See Also:Oracle Real Application Clusters Installation Guide for Microsoft Windows for more information about Oracle RAC executables requiring Windows Firewall exceptions