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Included in this gathered history is the SQL text, outline, bind variables, and compilation
environment. When a SQL statement is compiled, Oracle will first use the
cost-based optimizer to generate a plan and will evaluate any matching SQL plan
baselines for relative cost, choosing the plan with the lowest cost.
Comparing Optimizations
Oracle makes changes to the optimizer in every release. These changes are meant to
improve the overall quality of the decisions the optimizer makes, but a generally
improved optimizer could still create an execution plan for any particular SQL statement
that could result in a decrease in performance.
The SQL*Analyzer tool is designed to give youthe ability to recognize potential
problems caused by optimizer upgrades. This tool compares the execution plans for
the SQL statements in your application, flagging the ones in which the plans differ.
We recommend that youconsider using hints only when youhave determined them to
be absolutely necessary by thoroughly investigating the causes for an optimization
problem.


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