How much sampled history can be seen in V$ACTIVE_SESSION_HISTORY?
Oracle Database 10g stores the sampled active sessions in a circular buffer in SGA. Therefore, after a while the oldest session samples will be overwritten to make room for the latest session samples. The number of seconds of session activity that can be seen in V$ACTIVE_SESSION_HISTORY is dependent on the amount of activity in the database instance. The greater the database activity, the smaller is the number of seconds of session activity that can be seen in the V$ACTIVE_SESSION_HISTORY view. Typically, we expect 30 minutes of past session activity to be seen in this V$ view.
