Guenadi N Jilevski's Oracle BLOG


Oracle RAC 11g services

Oracle RAC 11g services

Oracle 11g RAC consists of many nodes with OS RDBMS & Clusterware.  Since Oracle 11g R2 the ASM &  OCR (grid)  are bundled together.


Now when a user connects to a database, it is preferable to connect to the service layer by mentioning the service in the connection string. As I mentioned above, we can create more services to address and logically differentiate the needs of the clients and applications without mingling into the nodes. Let’s see various service level deployments.

1.      Using Oracle Services

2.      Default Service Connections

3.      Connection Load Balancing

Oracle Services: This is a perfect way to manage applications or a subset of applications. Simply, OLTP users, DWH/Batch Operations can have their own services. Service level requirements should be the same for users /applications assigned to the same service. When defining a service, you have the opportunity to define which nodes will support that service. They become preferred instances while the ones that will provide failover support are known as available instances.

When you specify PREFERRED instances, then a particular set of instances are brought in to assist and support that service and the subset of applications. Should one or more of these PREFERRED instances fail, then the failover takes place and the services are moved over to the AVAILABLE instances. Should the failed instances come back online the services will not fall back to the PREFERRED instances simply because it has successfully met the service level requirement and is doing a fine job of providing high availability. Thus, there is no need to enact another outage to bring them back to the originally determined PREFERRED instances. Do however note that you can easily fail them back to the original situation by using FAN callouts.

Also, note that Resource profiles are automatically created when you define a service. A resource profile takes care of the manageability of the service and defines service dependencies for the instance and database. Stopping a service would mean stopping the database and the instances associated with the service, so use caution when you attempt to bring down the services.

Services are integrated with Resource Manager thus enabling us to restrict the resources that are being used by a service. Consumer groups are mapped to the services so users connecting are members of the specific consumer group. AWR (Automatic Workload Repository) helps us monitor the performance per service.

ONS (Oracle Net Services) provides connection load balancing. This can be simply done by setting the CLB goal in the listener, CLB_GOAL. It is also possible to specify a single TAF policy for all users of a specific service by defining the FAILOVER_METHOD, FAILOVER_TYPE, etc.

December 13, 2009 - Posted by | oracle

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