Plan Generator

 The plan generator tries out different plans for a submitted query. The optimizer chooses the plan with the lowest cost.

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For each nested subquery and unmerged view, the optimizer generates a subplan. The optimizer represents each subplan as a separate query block. The plan generator explores various plans for a query block by trying out different access paths, join methods, and join orders.

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The adaptive query optimization capability changes plans based on statistics collected during statement execution. All adaptive mechanisms can execute a final plan for a statement that differs from the default plan. Adaptive optimization uses either dynamic plans, which choose among subplans during statement execution, or reoptimization, which changes a plan on executions after the current execution.

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See also

• "Application and SQL Tuning"

• Oracle Database SQL Tuning Guide to learn about the optimizer components and adaptive optimization