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Donald K. Burleson

Oracle Utilities Tips

SQL Execution Statistics in 9i

The SQL tuning process prior to 9.2 involved executing SQL commands, then OS commands, and then SQL commands again. This is a very time-consuming and burdensome process. In 9.2, Oracle decided to retain the SQL metrics for each statement in the SGA (library cache) while the statement remains cached. The DBA could then diagnose SQL issues at a SQL prompt and leave tkprof alone. This is a vast improvement over prior versions.

Oracle9.2 contains the following views that enable the DBA to identify SQL issues directly from a SQL prompt. These views should be used to periodically check SQL statistics and full-table scans, alerting the DBA to problem areas requiring corrective action.

• v$sql_plan - This view shows the same information as shown by Explain Plan except it is the actual execution plan and not the predicted one – just like tkprof and even better than Explain Plan.

• v$sql_plan_statistics - This view contains the execution statistics for each operation (step) in the v$sql_plan. Queries should access this view and look for poor SQL operations including TABLE ACCESS FULL – full-table scans.

• v$sql_plan_statistics_all - This view combines data from v$sql_plan, v$sql_plan_statistics and v$sql_workarea.

Both v$sql_plan_statistics and v$sql_plan_statistics_all are not populated by default. The option statistics_level=all must be set.

To learn more about these techniques, see the book "Advanced Oracle Utilities: The Definitive Reference". 

You can buy it directly from the publisher and get instant access to the code depot of utilities scripts.



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