Chapter 16. Plan Stability and Control

Kerry Osborne

One of the most frustrating things about Oracle's Cost Based Optimizer (CBO) is its tendency to change plans for statements at seemingly random intervals. Of course, these changes are not random at all. But because the optimizer code is so complex, it's often difficult to determine why a plan changed. Oracle recognized this issue years ago and has been working to improve the situation for at least a decade. They have provided many tools for identifying when plans change and why they changed. They have also provided numerous tools that allow you to exert varying degrees of control over the execution plans that the optimizer chooses.

This chapter is made up of two main focus areas. The first focus ...

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