Active Session History
In Oracle Database 10g, the current session activity can be obtained from the V$SESSION or V$SESSION_WAIT views. The view V$SESSION_WAIT_HISTORY provides information about the last 10 wait events that the session encountered. However, for troubleshooting a performance issue, these views do not provide enough historical information about what the session did. Oracle Database 10g solves this problem with the introduction of Active Session History (ASH).
As the name suggests, Oracle provides historical information on active sessions. It samples all active sessions every second to track their state and stores this information in a buffer in the SGA.
TABLE 9-2. AWR Views (Not a Complete List)
The historical information is displayed ...
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