From 36c4bc6e725fe3e9b5a6cc7f1f83010534f18e4b 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 | 17 ++++++++++ src/test/regress/expected/stats_ext.out | 41 +++++++++++++++++++++++++ src/test/regress/sql/stats_ext.sql | 22 +++++++++++++ 5 files changed, 98 insertions(+) diff --git a/src/backend/statistics/dependencies.c b/src/backend/statistics/dependencies.c index 82b549fdc2..f1602cd3a2 100644 --- a/src/backend/statistics/dependencies.c +++ b/src/backend/statistics/dependencies.c @@ -24,6 +24,7 @@ #include "nodes/pathnodes.h" #include "optimizer/clauses.h" #include "optimizer/optimizer.h" +#include "parser/parsetree.h" #include "statistics/extended_stats_internal.h" #include "statistics/statistics.h" #include "utils/bytea.h" @@ -1410,11 +1411,19 @@ dependencies_clauselist_selectivity(PlannerInfo *root, int ndependencies; int i; AttrNumber attnum_offset; + RangeTblEntry *rte = planner_rt_fetch(rel->relid, root); /* unique expressions */ Node **unique_exprs; int unique_exprs_cnt; + /* + * 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)) return 1.0; diff --git a/src/backend/statistics/extended_stats.c b/src/backend/statistics/extended_stats.c index 4ab9aaa591..b23c15e9db 100644 --- a/src/backend/statistics/extended_stats.c +++ b/src/backend/statistics/extended_stats.c @@ -30,6 +30,7 @@ #include "nodes/nodeFuncs.h" #include "optimizer/clauses.h" #include "optimizer/optimizer.h" +#include "parser/parsetree.h" #include "pgstat.h" #include "postmaster/autovacuum.h" #include "statistics/extended_stats_internal.h" @@ -1694,6 +1695,14 @@ statext_mcv_clauselist_selectivity(PlannerInfo *root, List *clauses, int varReli List **list_exprs; /* expressions matched to any statistic */ int listidx; Selectivity sel = (is_or) ? 0.0 : 1.0; + 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 sel; /* 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 aff748d67b..9e39f9888e 100644 --- a/src/backend/utils/adt/selfuncs.c +++ b/src/backend/utils/adt/selfuncs.c @@ -3913,6 +3913,14 @@ estimate_multivariate_ndistinct(PlannerInfo *root, RelOptInfo *rel, Oid statOid = InvalidOid; MVNDistinct *stats; StatisticExtInfo *matched_info = 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) @@ -5222,6 +5230,7 @@ examine_variable(PlannerInfo *root, Node *node, int varRelid, foreach(slist, onerel->statlist) { StatisticExtInfo *info = (StatisticExtInfo *) lfirst(slist); + RangeTblEntry *rte = planner_rt_fetch(onerel->relid, root); ListCell *expr_item; int pos; @@ -5232,6 +5241,14 @@ examine_variable(PlannerInfo *root, Node *node, int varRelid, if (vardata->statsTuple) break; + /* + * When dealing with inheritance trees, ignore extended stats (which + * were built without data from child rels, and so do not represent + * them). + */ + if (rte->inh) + break; + /* skip stats without per-expression stats */ if (info->kind != STATS_EXT_EXPRESSIONS) continue; diff --git a/src/test/regress/expected/stats_ext.out b/src/test/regress/expected/stats_ext.out index c60ba45aba..abe1f89edd 100644 --- a/src/test/regress/expected/stats_ext.out +++ b/src/test/regress/expected/stats_ext.out @@ -176,6 +176,47 @@ 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; -- basic test for statistics on expressions CREATE TABLE ab1 (a INTEGER, b INTEGER, c TIMESTAMP, d TIMESTAMPTZ); -- expression stats may be built on a single expression column diff --git a/src/test/regress/sql/stats_ext.sql b/src/test/regress/sql/stats_ext.sql index 6fb37962a7..69d7b71f0e 100644 --- a/src/test/regress/sql/stats_ext.sql +++ b/src/test/regress/sql/stats_ext.sql @@ -112,6 +112,28 @@ 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; + -- basic test for statistics on expressions CREATE TABLE ab1 (a INTEGER, b INTEGER, c TIMESTAMP, d TIMESTAMPTZ);