Thursday, June 5, 2008

Understanding Optimization

Improvements in the Oracle Database 10g Optimizer make it even more valuable for tuning.

In Oracle Database 10g, the cost-based optimizer (CBO) has two modes—the normal mode and a tuning mode that is invoked by the SQL Tuning Advisor (and many other Oracle Database 10g advisors, such as the SQL Access Advisor). The SQL Tuning Advisor is a great new tool for DBAs in Oracle Database 10g. Specifically, in previous releases of Oracle, if you weren't happy with the plan created by the optimizer, you could hint your code to influence the optimizer's decision, but figuring that out is time-consuming at best. And even if you had the time to do all the analysis necessary to figure out the best execution plan, you can't touch the SQL generated by packaged applications—or any other application for which you didn't have access to the source code.

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