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 Author: Donald K. Burleson

Page: 1 2

Capturing wait event information was a burdensome process prior to Oraclre10g. Setting of special events and the reading of complex trace dumps had made the life of database administrators difficult. Fortunately, Oracle10g has simplified the way that wait event information is captured. Oracle 10g provides a wealth of new v$ and wrh$ views relating to Oracle wait events.

Time model:

Oracle10g has introduced several important new wait event v$ views. The Oracle 10g v$session_wait_history and v$sys_time_model views allow Oracle10g to capture system waits details in a time-series mode.

V$ View    DBA_HIST View
v$active_sess_hist  dba_hist_active_sess_history
v$sys_time_model  dba_hist_sys_time_model
v$active_session_history dba_hist_active_sess_history
v$event_histogram  No equivalent DBA view

Oracle10g Active Session History:

  • Oracle10g Active Session History (ASH) is amongst the most important area of Oracle10g wait event tuning.
  • ASH data is visualized through the v$active_sess_hist view and the wrh$active_session_history tables.
  • At a basic level, ASH stores the history of a recent session's activity and facilitates the analysis of the system performance at the current time.
  • ASH is designed as a rolling buffer in memory, and earlier information is overwritten when needed.
  • ASH uses the memory of the SGA.

Oracle10g hash key:

Oracle10g hash key allows you to track common session processes and allows inter-cal session tracking in cases like OCI session bouncing where each call to Oracle is a different session ID.

Oracle10g WRH$ wait event table:

ASH samples for wait events every second and tracks the waits in the new v$active_sess_hist view. New data values are written to the wrh$ tables every hour, or when a new AWR snapshot is taken. Below listing shows the Oracle10g WRH$ wait event table.

wrh$_active_session_history
wrh$_active_session_history_bl
wrh$_bg_event_summary
wrh$_event_name
wrh$_metric_name
wrh$_sessmetric_history
wrh$_sys_time_model
wrh$_sys_time_model_bl
wrh$_sysmetric_history
wrh$_sysmetric_summary
wrh$_sysstat
wrh$_sysstat_bl
wrh$_system_event
wrh$_system_event_bl
wrh$_waitclassmetric_history
wrh$_waitstat
wrh$_waitstat_bl

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