From b3cac25f4d50d66ef08a9a706df045c888578f8f 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 | 1 + src/backend/utils/adt/selfuncs.c | 8 ++++ src/test/regress/expected/stats_ext.out | 61 +++++++++++++++++++++++++ src/test/regress/sql/stats_ext.sql | 43 +++++++++++++++++ 5 files changed, 122 insertions(+) diff --git a/src/backend/statistics/dependencies.c b/src/backend/statistics/dependencies.c index 445a0db7c5..2d4c126279 100644 --- a/src/backend/statistics/dependencies.c +++ b/src/backend/statistics/dependencies.c @@ -23,6 +23,7 @@ #include "optimizer/var.h" #include "nodes/nodes.h" #include "nodes/relation.h" +#include "parser/parsetree.h" #include "statistics/extended_stats_internal.h" #include "statistics/statistics.h" #include "utils/bytea.h" @@ -961,10 +962,18 @@ dependencies_clauselist_selectivity(PlannerInfo *root, MVDependencies *dependencies; AttrNumber *list_attnums; int listidx; + RangeTblEntry *rte = planner_rt_fetch(rel->relid, root); /* initialize output argument */ *estimatedclauses = NULL; + /* + * 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 0ad029f5cf..44c24b7939 100644 --- a/src/backend/statistics/extended_stats.c +++ b/src/backend/statistics/extended_stats.c @@ -23,6 +23,7 @@ #include "catalog/pg_collation.h" #include "catalog/pg_statistic_ext.h" #include "nodes/relation.h" +#include "parser/parsetree.h" #include "postmaster/autovacuum.h" #include "statistics/extended_stats_internal.h" #include "statistics/statistics.h" diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c index b72edae4ca..d88dd1cc85 100644 --- a/src/backend/utils/adt/selfuncs.c +++ b/src/backend/utils/adt/selfuncs.c @@ -3923,6 +3923,14 @@ 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 bb71459648..b0af5e940b 100644 --- a/src/test/regress/expected/stats_ext.out +++ b/src/test/regress/expected/stats_ext.out @@ -1,4 +1,24 @@ -- Generic extended statistics support +-- check the number of estimated/actual rows in the top node +create function check_estimated_rows(text) returns table (estimated int, actual int) +language plpgsql as +$$ +declare + ln text; + tmp text[]; + first_row bool := true; +begin + for ln in + execute format('explain analyze %s', $1) + loop + if first_row then + first_row := false; + tmp := regexp_match(ln, 'rows=(\d*) .* rows=(\d*)'); + return query select tmp[1]::int, tmp[2]::int; + end if; + end loop; +end; +$$; -- We will be checking execution plans without/with statistics, so -- let's make sure we get simple non-parallel plans. Also set the -- work_mem low so that we can use small amounts of data. @@ -107,6 +127,47 @@ 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 7a13d26e8d..88e77877ff 100644 --- a/src/test/regress/sql/stats_ext.sql +++ b/src/test/regress/sql/stats_ext.sql @@ -1,5 +1,26 @@ -- Generic extended statistics support +-- check the number of estimated/actual rows in the top node +create function check_estimated_rows(text) returns table (estimated int, actual int) +language plpgsql as +$$ +declare + ln text; + tmp text[]; + first_row bool := true; +begin + for ln in + execute format('explain analyze %s', $1) + loop + if first_row then + first_row := false; + tmp := regexp_match(ln, 'rows=(\d*) .* rows=(\d*)'); + return query select tmp[1]::int, tmp[2]::int; + end if; + end loop; +end; +$$; + -- We will be checking execution plans without/with statistics, so -- let's make sure we get simple non-parallel plans. Also set the -- work_mem low so that we can use small amounts of data. @@ -74,6 +95,28 @@ 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;