AWR is the infrastructure

AWR is the infrastructure that provides services to Oracle Database 11g components to collect, maintain, and utilize statistics for problem detection and self-tuning purposes.

The AWR infrastructure consists of two major parts:

•An in-memory statistics collection facility that is used by various components to collect statistics. These statistics are stored in memory for performance reasons. Statistics stored in memory are accessible through dynamic performance (V$) views.

•AWR snapshots represent the persistent portion of the facility. The AWR snapshots are accessible through data dictionary (DBA) views and Database Control.

Statistics are stored in persistent storage for several reasons:

•The statistics need to survive instance crashes.

•Historical data for baseline comparisons is needed for certain types of analysis.

•Memory overflow: When old statistics are replaced by new ones due to memory shortage, the replaced data can be stored for later use.

The memory version of the statistics is transferred to disk on a regular basis by a background process called MMON (Manageability Monitor).

With AWR, the Oracle database server provides a way to capture historical statistics data automatically, without the intervention of DBAs.