From 76569ad6f423f56f655699f57c39298af2111914 Mon Sep 17 00:00:00 2001 From: Tomas Vondra Date: Sat, 15 Jan 2022 02:15:23 +0100 Subject: [PATCH] Ignore extended statistics for inheritance trees Since commit 859b3003de we only build extended statistics for individual relations, ignoring the child relations. This resolved the issue with updating catalog tuple twice, but we still tried to use the statistics when calculating estimates for the whole inheritance tree. When the relations contain very distinct data, it may produce bogus estimates. This is roughly the same issue 427c6b5b9 addressed ~15 years ago, and we fix it the same way - by ignoring extended statistics when calculating estimates for the inheritance tree as a whole. We still consider extended statistics when calculating estimates for individual child relations, of course. This may result in plan changes due to different estimates, but if the old statistics were not describing the inheritance tree particularly well it's quite likely the new plans is actually better. Report and patch by Justin Pryzby, minor fixes and cleanup by me. Backpatch all the way back to PostgreSQL 10, where extended statistics were introduced (same as 859b3003de). Author: Justin Pryzby Reported-by: Justin Pryzby Backpatch-through: 10 Discussion: https://postgr.es/m/20210923212624.GI831%40telsasoft.com --- src/backend/statistics/dependencies.c | 9 ++++++ src/backend/statistics/extended_stats.c | 9 ++++++ src/backend/utils/adt/selfuncs.c | 8 +++++ src/test/regress/expected/stats_ext.out | 41 +++++++++++++++++++++++++ src/test/regress/sql/stats_ext.sql | 22 +++++++++++++ 5 files changed, 89 insertions(+) diff --git a/src/backend/statistics/dependencies.c b/src/backend/statistics/dependencies.c index bdc7e25045..12f58e0ffd 100644 --- a/src/backend/statistics/dependencies.c +++ b/src/backend/statistics/dependencies.c @@ -24,6 +24,7 @@ #include "optimizer/optimizer.h" #include "nodes/nodes.h" #include "nodes/pathnodes.h" +#include "parser/parsetree.h" #include "statistics/extended_stats_internal.h" #include "statistics/statistics.h" #include "utils/bytea.h" @@ -963,6 +964,14 @@ dependencies_clauselist_selectivity(PlannerInfo *root, MVDependencies *dependencies; Bitmapset **list_attnums; int listidx; + RangeTblEntry *rte = planner_rt_fetch(rel->relid, root); + + /* + * When dealing with inheritance trees, ignore extended stats (which were + * built without data from child rels, and thus do not represent them). + */ + if (rte->inh) + return 1.0; /* check if there's any stats that might be useful for us. */ if (!has_stats_of_kind(rel->statlist, STATS_EXT_DEPENDENCIES)) diff --git a/src/backend/statistics/extended_stats.c b/src/backend/statistics/extended_stats.c index e0aece6b51..6593eb6c2d 100644 --- a/src/backend/statistics/extended_stats.c +++ b/src/backend/statistics/extended_stats.c @@ -28,6 +28,7 @@ #include "nodes/nodeFuncs.h" #include "optimizer/clauses.h" #include "optimizer/optimizer.h" +#include "parser/parsetree.h" #include "postmaster/autovacuum.h" #include "statistics/extended_stats_internal.h" #include "statistics/statistics.h" @@ -1075,6 +1076,14 @@ statext_mcv_clauselist_selectivity(PlannerInfo *root, List *clauses, int varReli mcv_totalsel, other_sel, sel; + RangeTblEntry *rte = planner_rt_fetch(rel->relid, root); + + /* + * When dealing with inheritance trees, ignore extended stats (which were + * built without data from child rels, and thus do not represent them). + */ + if (rte->inh) + return 1.0; /* check if there's any stats that might be useful for us. */ if (!has_stats_of_kind(rel->statlist, STATS_EXT_MCV)) diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c index 1ce5eb268b..10a83e27ea 100644 --- a/src/backend/utils/adt/selfuncs.c +++ b/src/backend/utils/adt/selfuncs.c @@ -3641,6 +3641,14 @@ estimate_multivariate_ndistinct(PlannerInfo *root, RelOptInfo *rel, Oid statOid = InvalidOid; MVNDistinct *stats; Bitmapset *matched = NULL; + RangeTblEntry *rte = planner_rt_fetch(rel->relid, root); + + /* + * When dealing with inheritance trees, ignore extended stats (which were + * built without data from child rels, and thus do not represent them). + */ + if (rte->inh) + return false; /* bail out immediately if the table has no extended statistics */ if (!rel->statlist) diff --git a/src/test/regress/expected/stats_ext.out b/src/test/regress/expected/stats_ext.out index 06521a426a..3ad2156794 100644 --- a/src/test/regress/expected/stats_ext.out +++ b/src/test/regress/expected/stats_ext.out @@ -124,6 +124,47 @@ CREATE STATISTICS ab1_a_b_stats ON a, b FROM ab1; ANALYZE ab1; DROP TABLE ab1 CASCADE; NOTICE: drop cascades to table ab1c +-- Tests for stats with inheritance +CREATE TABLE stxdinh(a int, b int); +CREATE TABLE stxdinh1() INHERITS(stxdinh); +CREATE TABLE stxdinh2() INHERITS(stxdinh); +INSERT INTO stxdinh SELECT mod(a,50), mod(a,100) FROM generate_series(0, 1999) a; +INSERT INTO stxdinh1 SELECT mod(a,100), mod(a,100) FROM generate_series(0, 999) a; +INSERT INTO stxdinh2 SELECT mod(a,100), mod(a,100) FROM generate_series(0, 999) a; +VACUUM ANALYZE stxdinh, stxdinh1, stxdinh2; +-- Ensure non-inherited stats are not applied to inherited query +-- Without stats object, it looks like this +SELECT * FROM check_estimated_rows('SELECT a, b FROM stxdinh* GROUP BY 1, 2'); + estimated | actual +-----------+-------- + 400 | 150 +(1 row) + +SELECT * FROM check_estimated_rows('SELECT a, b FROM stxdinh* WHERE a = 0 AND b = 0'); + estimated | actual +-----------+-------- + 3 | 40 +(1 row) + +CREATE STATISTICS stxdinh ON a, b FROM stxdinh; +VACUUM ANALYZE stxdinh, stxdinh1, stxdinh2; +-- Since the stats object does not include inherited stats, it should not +-- affect the estimates +SELECT * FROM check_estimated_rows('SELECT a, b FROM stxdinh* GROUP BY 1, 2'); + estimated | actual +-----------+-------- + 400 | 150 +(1 row) + +-- Dependencies are applied at individual relations (within append), so +-- this estimate changes a bit because we improve estimates for the parent +SELECT * FROM check_estimated_rows('SELECT a, b FROM stxdinh* WHERE a = 0 AND b = 0'); + estimated | actual +-----------+-------- + 22 | 40 +(1 row) + +DROP TABLE stxdinh, stxdinh1, stxdinh2; -- Verify supported object types for extended statistics CREATE schema tststats; CREATE TABLE tststats.t (a int, b int, c text); diff --git a/src/test/regress/sql/stats_ext.sql b/src/test/regress/sql/stats_ext.sql index 06a2caff7b..4fd7ed1b81 100644 --- a/src/test/regress/sql/stats_ext.sql +++ b/src/test/regress/sql/stats_ext.sql @@ -92,6 +92,28 @@ CREATE STATISTICS ab1_a_b_stats ON a, b FROM ab1; ANALYZE ab1; DROP TABLE ab1 CASCADE; +-- Tests for stats with inheritance +CREATE TABLE stxdinh(a int, b int); +CREATE TABLE stxdinh1() INHERITS(stxdinh); +CREATE TABLE stxdinh2() INHERITS(stxdinh); +INSERT INTO stxdinh SELECT mod(a,50), mod(a,100) FROM generate_series(0, 1999) a; +INSERT INTO stxdinh1 SELECT mod(a,100), mod(a,100) FROM generate_series(0, 999) a; +INSERT INTO stxdinh2 SELECT mod(a,100), mod(a,100) FROM generate_series(0, 999) a; +VACUUM ANALYZE stxdinh, stxdinh1, stxdinh2; +-- Ensure non-inherited stats are not applied to inherited query +-- Without stats object, it looks like this +SELECT * FROM check_estimated_rows('SELECT a, b FROM stxdinh* GROUP BY 1, 2'); +SELECT * FROM check_estimated_rows('SELECT a, b FROM stxdinh* WHERE a = 0 AND b = 0'); +CREATE STATISTICS stxdinh ON a, b FROM stxdinh; +VACUUM ANALYZE stxdinh, stxdinh1, stxdinh2; +-- Since the stats object does not include inherited stats, it should not +-- affect the estimates +SELECT * FROM check_estimated_rows('SELECT a, b FROM stxdinh* GROUP BY 1, 2'); +-- Dependencies are applied at individual relations (within append), so +-- this estimate changes a bit because we improve estimates for the parent +SELECT * FROM check_estimated_rows('SELECT a, b FROM stxdinh* WHERE a = 0 AND b = 0'); +DROP TABLE stxdinh, stxdinh1, stxdinh2; + -- Verify supported object types for extended statistics CREATE schema tststats;