filter push-down

FPD - filter push-down

Filter pushdown is part from query transformations. Query transformation was based on heuristic rules in 9i. From 10G R1 however by default query transformations are cost based since"_optimizer_cost_based_transformation" defaults to linear. ( there are / were bugs related to cost based query transformation causing huge performance degradation )

since 11.2.0.3 filter pushdown can be controlled with "_optimizer_filter_pushdown", It defaults to true so FPD will happen whenever the optimizer think it is appropriate.

FPD相对比较简单，就不多说了。

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