With this capability, you can test actual production scenarios against new
configurations or versions of the database, and Database Replay will spot areas of
potential performance problems on the changed platform.
Performance and Optimization
The purpose of the optimizer is to select the best execution plan for your queries. But
there is a lot more to optimizing the overall performance of your database. Oracle
performance is the subject of Chapter 7 of this book.
Understanding the Execution Plan
Oracle??™s query optimizer automatically selects an execution plan for each query
submitted. By and large, although the optimizer does a good job of selecting the execution
plan, there may be times when the performance of the database suggests that
it is using a less-than-optimal execution plan.
The only way youcan really tell what path is being selected by the optimizer is to see
the layout of the execution plan. You can use two Oracle character-mode utilities to
examine the execution plan chosen by the Oracle optimizer. These tools allow you to
see the successive steps used by Oracle to collect, select, and return the data to the
user.
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