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Properly prepare varinfos in estimate_multivariate_bucketsize()

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To estimate with extended statistics, we need to clear the varnullingrels
field in the expression, and duplicates are not allowed in the GroupVarInfo
list.  We might re-use add_unique_group_var(), but we don't do so for two
reasons.

  1) We must keep the origin_rinfos list ordered exactly the same way as
     varinfos.
  2) add_unique_group_var() is designed for estimate_num_groups(), where a
     larger number of groups is worse.   While estimating the number of hash
     buckets, we have the opposite: a lesser number of groups is worse.
     Therefore, we don't have to remove "known equal" vars: the removed var
     may valuably contribute to the multivariate statistics to grow the number
     of groups.

This commit adds custom code to estimate_multivariate_bucketsize() to
initialize varinfos properly.

Reported-by: Robins Tharakan <tharakan@gmail.com>
Discussion: https://postgr.es/m/18885-da51324078588253%40postgresql.org
Author: Andrei Lepikhov <lepihov@gmail.com>
Reviewed-by: David Rowley <dgrowleyml@gmail.com>
Reviewed-by: Tomas Vondra <tomas@vondra.me>
Reviewed-by: Alexander Korotkov <aekorotkov@gmail.com>
This commit is contained in:
Alexander Korotkov
2025-04-23 20:13:51 +03:00
parent 3db61db48e
commit 9f404d7922
3 changed files with 96 additions and 3 deletions
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28
src/test/regress/expected/stats_ext.out
View File

@@ -3427,4 +3427,32 @@ SELECT * FROM sb_1 a, sb_2 b WHERE a.x = b.x AND a.y = b.y AND a.z = b.z;
-> Seq Scan on sb_2 b
(5 rows)
-- Check that the Hash Join bucket size estimator detects equal clauses correctly.
SET enable_nestloop = 'off';
SET enable_mergejoin = 'off';
EXPLAIN (COSTS OFF)
SELECT FROM sb_1 LEFT JOIN sb_2 ON (sb_2.x=sb_1.x) AND (sb_1.x=sb_2.x);
QUERY PLAN
--------------------------------------------------------
Hash Left Join
Hash Cond: ((sb_1.x = sb_2.x) AND (sb_1.x = sb_2.x))
-> Seq Scan on sb_1
-> Hash
-> Seq Scan on sb_2
(5 rows)
EXPLAIN (COSTS OFF)
SELECT FROM sb_1 LEFT JOIN sb_2
ON (sb_2.x=sb_1.x) AND (sb_1.x=sb_2.x) AND (sb_1.y=sb_2.y);
QUERY PLAN
------------------------------------------------------------------------------
Hash Left Join
Hash Cond: ((sb_1.x = sb_2.x) AND (sb_1.y = sb_2.y) AND (sb_1.x = sb_2.x))
-> Seq Scan on sb_1
-> Hash
-> Seq Scan on sb_2
(5 rows)
RESET enable_nestloop;
RESET enable_mergejoin;
DROP TABLE sb_1, sb_2 CASCADE;

11
src/test/regress/sql/stats_ext.sql
View File

@@ -1747,4 +1747,15 @@ ANALYZE sb_2;
EXPLAIN (COSTS OFF) -- Choose hash join
SELECT * FROM sb_1 a, sb_2 b WHERE a.x = b.x AND a.y = b.y AND a.z = b.z;
-- Check that the Hash Join bucket size estimator detects equal clauses correctly.
SET enable_nestloop = 'off';
SET enable_mergejoin = 'off';
EXPLAIN (COSTS OFF)
SELECT FROM sb_1 LEFT JOIN sb_2 ON (sb_2.x=sb_1.x) AND (sb_1.x=sb_2.x);
EXPLAIN (COSTS OFF)
SELECT FROM sb_1 LEFT JOIN sb_2
ON (sb_2.x=sb_1.x) AND (sb_1.x=sb_2.x) AND (sb_1.y=sb_2.y);
RESET enable_nestloop;
RESET enable_mergejoin;
DROP TABLE sb_1, sb_2 CASCADE;