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Pro Oracle SQL, Second Edition by Jared Still, Riyaj Shamsudeen, Robyn Sands, Kerry Osborne, Karen Morton

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CHAPTER 16

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Plan Stability

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 changes. Oracle recognized this issue years ago and has been working to improve the situation for at least a decade. It has provided many tools for identifying when plans change and why they change. Oracle has also provided numerous tools that allow you to exert varying degrees of control over the execution plans the optimizer ...

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