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Don Burleson Blog 







Keeping long-term 10g performance metrics

Oracle Tips by Burleson Consulting
April 13, 2004
Don Burleson

There is an important issue with the 10g AWR because the default collection retention is only seven days.  Frequently you will want to increase this threshold so that you have long-term performance data for complex performance analysis using the dba_hist views.  Let's take a quick look at how this works.

The new Oracle10g automating polling mechanism collects a huge amount of performance data from Oracle and stored it for time-based analysis. Please do not confuse this feature with the automatic collection of statistics for the cost-based SQL optimizer which is governed by the statistcis_level initialization parameter (the default behavior for CBO statistics collection is to user the ?monitoring? function to detect when tables have changed enough to warrant re-computation of SQL optimizer statistics).

The performance data collection process involves the capture of in-memory statistics from the v$ views and their transfer to the wrh$ tables. The new MMON background process does the data collection process, running every 30 minutes. The exception is the time-base wait collection model that runs every 60 seconds, collecting elapsed-time wait event information.

The default collection for AWR data is only seven days, so many Oracle DBAs will increase the storage of detail information over longer time periods using the new dbms package called dbms_workload_repository.modify_snapshot_settings. This will change the retention period and collection frequency to provide you with longer timer periods of data:

execute dbms_workload_repository.modify_snapshot_settings(
interval => 60,
retention => 43200);

In this example the retention period is specified as 30 days (43200 min) and the interval between each snapshot is 60 min. If you query the dba_hist_wr_control view after this procedure is executed, you will see the changes to these settings. 



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