Services in Oracle RAC

Based on the number of instances participating in your Oracle RAC Cluster and complexity and objectives of your application’s environment we need to choose optimal workload management. And there variety of considerations based on that.

We can use following features of Oracle RAC to manage workload :

1. Oracle Services
2. Database Resource Manager
3. Oracle Rac High Availability Framework
4. FAN[Fast Application Notification]
5. Load Balancing Advisory
6. Connection Load Balancing

In this article we are going to cover Oracle Services.

First of all What is Services

In Single Instance database we use service for separating workloads and we can administer it well.

The services are tightly integrated with Oracle Database and are maintained in the data dictionary. Application team can define service name while connecting to database and if no service is defined , database will be connected with default service which has same name as database name.

We can check service name using service_names parameter

SQL> show parameter service_names

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
service_names                        string      orcl
SQL>

In Oracle RAC , Services are having much more features than just separating workload and administer it.

A service is a logical grouping of sessions performing similar kind of work.Services enable you to group database workloads and route work to the optimal instances that are assigned to offer the service

For services ,It is recommended that all the users who connect using a service have the same service-level requirements.

Advantages of using Services :

1. High Availability  : In Oracle RAC we can set preferred and available instance for specific service. Which gives advantage. In case of Instance crash , service will be automatically redirected to a available instance.
2. Services makes the work more manageable and tunable. For example , all on-line users can use one service whereas batch users can use another service and reporting can use yet another service.
3. Tracing can be also enabled for all sessions who connect using a service. This is useful to identify culprit session connected using a particular service. Performance statistics are collected and aggregated by service: This can be used to find out the performance of all the sessions belonging to a service.
4. We can SERVICE_ELAPSED_TIME and SERVICE_CPU_TIME performance threshold . The AWR report monitors the service time and CPU time and publishes alerts when the performance exceeds the thresholds. With this information we can modify services accordingly.
5.