AWR(Automatic Workload Repository)

This component is the central element of the new manageability infrastructure. It provides services to internal Oracle server components to collect, process, maintain, and access performance statistics for problem detection and self-tuning purposes.

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AWR is the infrastructure that provides services to Oracle Database 10g 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 Oracle Database 10g 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 views and Database Control.

Statistics are stored in persistent storage for several reasons:
The statistics need to survive instance crashes.
Some analyses need historical data for baseline comparisons.
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 new background process called MMON (Manageability Monitor).