The Automatic Workload Repository (AWR) collects, processes, and maintains performance statistics for the database. The gathered data can be displayed in both reports and views. If you use services with your database, then AWR tracks metrics at the service level.
Metrics can be measured against a variety of units, including time, transactions, or database calls. For example, the number of database calls per second is a metric. Server generated alerts can be placed on these metrics when they exceed or fail to meet user-specified thresholds. The database or system administrator can then respond, for example, by:
Using the Oracle Database Resource Manager to configure the service level for one service to have priorities relative to other services
Stopping overloaded processes
Modifying a service level requirement
Implementing recovery scenarios in response to service quality changes
Using AWR metrics and performance alerts enables you to maintain continued service availability despite service level changes. It also enables you to measure the quality of service provided by the database services.
The AWR ensures that the Oracle Clusterware workload management framework and the database resource manager have persistent and global representations of performance data. This information helps Oracle Database schedule job classes by service and to assign priorities to consumer groups. If necessary, you can rebalance workloads manually with either Oracle Enterprise Manager or SRVCTL. You can also disconnect a series of sessions, but leave the service running.
Oracle does not recommend using the DBMS_SERVICE package for use with services used by an Oracle RAC database. Use SRVCTL or Oracle Enterprise Manager to create database services for Oracle RAC.
Oracle Database 2 Day + Performance Tuning Guide for more information on creating alerts for metric thresholds
Oracle Database Performance Tuning Guide for more information about the Automatic Workload Repository
Oracle Database PL/SQL Packages and Types Reference for details about Oracle Database packages