Inside the Automatic Workload Repository Tables

In all versions prior to Oracle Database10g, the v$ views never captured time-series data. Administrators were forced to take snapshots using BSTAT-ESTAT or STATSPACK to see the changes over time.  Oracle Database10g introduces new v$ metric tables, v$eventmetric, v$waitclassmetric and v$waitclassmetric_history, which keep elapsed-time data.

In 10g, all v$ views that contain the BEGIN_TIME and END_TIME columns are used to store performance information. Because of the transient nature of the v$ views, this information needed to be persistent. This was accomplished by the introduction of the wrh$ tables in Oracle Database 10g.  The next section will provide a more detailed examination of the wrh$ wait event structure.

The AWR and ASH Wait Event Tables

Oracle Database 10g has radically changed the way it captures wait event information. There are a host of new v$ and wrh$ views related to Oracle wait events.  The list of wait events has been expanded and Oracle Database 10g now captures statistics on over 800 specific wait events.  The new wait events are a result of separating latch waits into their individual components and separating enqueue waits or locks into a finer level of granularity.

The foundation of the new wait event architecture is called the time model.  Oracle has introduced several important new wait event v$ views in 10g.