Automatic Workload Repository in Oracle RAC Environments

You can use Automatic Workload Repository (AWR) to monitor performance statistics related to Oracle RAC databases. AWR automatically generates snapshots of the performance data once every hour and collects the statistics in the workload repository. In Oracle RAC environments, each AWR snapshot captures data from all active instances in the cluster. The data for each snapshot set is captured from the same point in time. AWR stores the snapshot data for all instances in the same table and the data is identified by an instance qualifier. For example, the BUFFER_BUSY_WAIT statistic shows the number of buffer waits on each instance. AWR does not store data that is aggregated from across the entire cluster. In other words, the data is stored for each individual instance.

Using the Automatic Database Diagnostic Monitor (ADDM), you can analyze the information collected by AWR for possible performance problems with Oracle Database. ADDM presents performance data from a cluster-wide perspective, thus enabling you to analyze performance on a global basis. In an Oracle RAC environment, ADDM can analyze performance using data collected from all instances and present it at different levels of granularity, including:

  • Analysis for the entire cluster

  • Analysis for a specific database instance

  • Analysis for a subset of database instances

To perform these analyses, you can run the ADDM Advisor in ADDM for Oracle RAC mode to perform an analysis of the entire cluster; in Local ADDM mode to analyze the performance of an individual instance; or in Partial ADDM mode to analyze a subset of instances. Activate ADDM analysis using the advisor framework through Advisor Central in Oracle Enterprise Manager, or through the DBMS_ADVISOR and DBMS_ADDM PL/SQL packages.

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