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Use Foreign Key relationships to infer multi-column join selectivity
In cases where joins use multiple columns we currently assess each joinseparately causing gross mis-estimates for join cardinality.This patch adds use of FK information for the first time into theplanner. When FKs are present and we have multi-column join information,plan estimates will be drastically improved. Cases with multiple FKsare handled, though partial matches are ignored currently.Net effect is substantial performance improvements for joins in manycommon cases. Additional planning time is isolated to cases that arecurrently performing poorly, measured at 0.08 - 0.15 ms.Please watch for planner performance regressions; circumstances seemunlikely but the law of unintended consequences may apply somewhen.Additional complex tests welcome to prove this before release.Tests can be performed using SET enable_fkey_estimates = on | offusing scripts provided during Hackers discussions, message id:552335D9.3090707@2ndquadrant.comAuthors: Tomas Vondra and David RowleyReviewed and tested by Simon Riggs, adding comments only1 parent6928484 commit137805f
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