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Use Foreign Key relationships to infer multi-column join selectivity

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In cases where joins use multiple columns we currently assess each join
separately causing gross mis-estimates for join cardinality.

This patch adds use of FK information for the first time into the
planner. When FKs are present and we have multi-column join information,
plan estimates will be drastically improved. Cases with multiple FKs
are handled, though partial matches are ignored currently.

Net effect is substantial performance improvements for joins in many
common cases. Additional planning time is isolated to cases that are
currently performing poorly, measured at 0.08 - 0.15 ms.

Please watch for planner performance regressions; circumstances seem
unlikely 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 | off
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Authors: Tomas Vondra and David Rowley
Reviewed and tested by Simon Riggs, adding comments only
This commit is contained in:
Simon Riggs
2016-04-08 02:51:09 +01:00
parent 6928484bda
commit 137805f89a
5 changed files with 392 additions and 24 deletions
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29
src/test/regress/expected/rangefuncs.out
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@ -1,18 +1,19 @@
SELECT name, setting FROM pg_settings WHERE name LIKE 'enable%';
name | setting
----------------------+---------
enable_bitmapscan | on
enable_hashagg | on
enable_hashjoin | on
enable_indexonlyscan | on
enable_indexscan | on
enable_material | on
enable_mergejoin | on
enable_nestloop | on
enable_seqscan | on
enable_sort | on
enable_tidscan | on
(11 rows)
name | setting
-----------------------+---------
enable_bitmapscan | on
enable_fkey_estimates | on
enable_hashagg | on
enable_hashjoin | on
enable_indexonlyscan | on
enable_indexscan | on
enable_material | on
enable_mergejoin | on
enable_nestloop | on
enable_seqscan | on
enable_sort | on
enable_tidscan | on
(12 rows)
CREATE TABLE foo2(fooid int, f2 int);
INSERT INTO foo2 VALUES(1, 11);