Services provide location transparency. A service name can identify multiple database instances, and an instance can belong to multiple services. Several database features use services for an Oracle RAC database:
This section includes the following topics:
Resource profiles are automatically created when you define a service. A resource profile describes how Oracle Clusterware should manage the service and which instance the service should failover to if the preferred instance stops. Resource profiles also define service dependencies for the instance and the database. Due to these dependencies, if you stop a database, then the instances and services are automatically stopped in the correct order.
Services are integrated with Oracle Resource Manager, which enables you to restrict the resources that users use to connect to an instance by using a service. Oracle Resource Manager enables you to map a consumer group to a service so that users who connect to an instance using that service are members of the specified consumer group. Oracle Resource Manager operates at an instance level.
The metric data generated by Automatic Workload Repository (AWR) is organized into various groups, such as event, event class, session, service, and tablespace metrics. Typically, you view the AWR data using Oracle Enterprise Manager or AWR reports.
Oracle Database Performance Tuning Guide for more information about generating and viewing AWR reports
By default, in an Oracle RAC environment, a SQL statement executed in parallel can run across all of the nodes in the cluster. For this cross-node or inter-node parallel execution to perform well, the interconnect in the Oracle RAC environment must be sized appropriately because inter-node parallel execution may result in a lot of interconnect traffic. To limit inter-node parallel execution, you can control parallel execution in an Oracle RAC environment using the
PARALLEL_FORCE_LOCAL initialization parameter. By setting this parameter to
TRUE, the parallel execution servers can only execute on the same Oracle RAC node where the SQL statement was started.
Services are used to limit the number of instances that participate in a parallel SQL operation. When the default database service is used, the parallel SQL operation can run on all available instances. You can create any number of services, each consisting of one or more instances. When a parallel SQL operation is started, the parallel execution servers are only spawned on instances which offer the specified service used in the initial database connection.
PARALLEL_INSTANCE_GROUP is an Oracle RAC parameter that, when used with services, lets you restrict parallel query operations to a limited number of instances.To restrict parallel query operations to a limited number of instances, set the
PARALLEL_INSTANCE_GROUP initialization parameter to the name of a service. This does not affect other parallel operations such as parallel recovery or the processing of
Oracle Streams takes advantage of Oracle RAC features in many ways. When Oracle Streams is configured in an Oracle RAC environment, each queue table has an owning instance. If the instance that hosts a queue table fails, another instance in the Oracle RAC database becomes the owning instance for the queue table, allowing Oracle Streams to continue operating.
Also, on an Oracle RAC database, a service is created for each buffered queue. This service always runs on the owner instance of the destination queue and follows the ownership of this queue if the ownership switches because of instance startup, instance shutdown, and so on. This service is used by queue-to-queue propagations.
Oracle Streams Concepts and Administration for more information