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Skip system attributes when applying mvdistinct stats

author Tomas Vondra <tomas.vondra@postgresql.org>

2019年11月16日 00:17:15 +0000 (01:17 +0100)

committer Tomas Vondra <tomas.vondra@postgresql.org>

2019年11月16日 00:58:38 +0000 (01:58 +0100)

When estimating number of distinct groups, we failed to ignore system
attributes when matching the group expressions to mvdistinct stats,
causing failures like

ERROR: negative bitmapset member not allowed

Fix that by simply skipping anything that is not a regular attribute.
Backpatch to PostgreSQL 10, where the extended stats were introduced.

Bug: #16111
Reported-by: Tuomas Leikola
Author: Tomas Vondra
Backpatch-through: 10
Discussion: https://postgr.es/m/16111-687799584c3a7e73@postgresql.org

src/backend/utils/adt/selfuncs.c patch | blob | blame | history

src/test/regress/expected/stats_ext.out patch | blob | blame | history

src/test/regress/sql/stats_ext.sql patch | blob | blame | history

diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c

index 7622edb9dd4cc52ccc8a26a3f2f0119a8f3cd6ea..126ffad67d0ae3851cc1f1bb4889e86d0ec07cc3 100644 (file)

--- a/src/backend/utils/adt/selfuncs.c

+++ b/src/backend/utils/adt/selfuncs.c

@@ -3931,14 +3931,19 @@ estimate_multivariate_ndistinct(PlannerInfo *root, RelOptInfo *rel,

foreach(lc, *varinfos)

{

GroupVarInfo *varinfo = (GroupVarInfo *) lfirst(lc);

+ AttrNumber attnum;

Assert(varinfo->rel == rel);

- if (IsA(varinfo->var, Var))

- {

- attnums = bms_add_member(attnums,

- ((Var *) varinfo->var)->varattno);

- }

+ if (!IsA(varinfo->var, Var))

+ continue;

+

+ attnum = ((Var *) varinfo->var)->varattno;

+

+ if (!AttrNumberIsForUserDefinedAttr(attnum))

+ continue;

+

+ attnums = bms_add_member(attnums, attnum);

}

/* look for the ndistinct statistics matching the most vars */

@@ -4018,6 +4023,10 @@ estimate_multivariate_ndistinct(PlannerInfo *root, RelOptInfo *rel,

}

attnum = ((Var *) varinfo->var)->varattno;

+

+ if (!AttrNumberIsForUserDefinedAttr(attnum))

+ continue;

+

if (!bms_is_member(attnum, matched))

newlist = lappend(newlist, varinfo);

}

diff --git a/src/test/regress/expected/stats_ext.out b/src/test/regress/expected/stats_ext.out

index eebf250998e1959c03b2d21e17911ced0753d793..5b7e1d466088eeab330822c5c439e0c0e0bd8fbc 100644 (file)

--- a/src/test/regress/expected/stats_ext.out

+++ b/src/test/regress/expected/stats_ext.out

@@ -217,6 +217,18 @@ SELECT stxkind, stxndistinct

{d,f} | {"3, 4": 301, "3, 6": 301, "4, 6": 301, "3, 4, 6": 301}

(1 row)

+-- minor improvement, make sure the ctid does not break the matching

+EXPLAIN (COSTS off)

+SELECT COUNT(*) FROM ndistinct GROUP BY ctid, a, b;

+ QUERY PLAN

+-----------------------------------

+ GroupAggregate

+ Group Key: ctid, a, b

+ -> Sort

+ Sort Key: ctid, a, b

+ -> Seq Scan on ndistinct

+(5 rows)

+

-- Hash Aggregate, thanks to estimates improved by the statistic

EXPLAIN (COSTS off)

SELECT COUNT(*) FROM ndistinct GROUP BY a, b;

diff --git a/src/test/regress/sql/stats_ext.sql b/src/test/regress/sql/stats_ext.sql

index 43ff77c5344e0f2b07bd5c5585da67e566d1c51f..2543dbfffa70ff800061451f1ff7968c4b75f7dd 100644 (file)

--- a/src/test/regress/sql/stats_ext.sql

+++ b/src/test/regress/sql/stats_ext.sql

@@ -144,6 +144,10 @@ ANALYZE ndistinct;

SELECT stxkind, stxndistinct

FROM pg_statistic_ext WHERE stxrelid = 'ndistinct'::regclass;

+-- minor improvement, make sure the ctid does not break the matching

+EXPLAIN (COSTS off)

+SELECT COUNT(*) FROM ndistinct GROUP BY ctid, a, b;

+

-- Hash Aggregate, thanks to estimates improved by the statistic

EXPLAIN (COSTS off)

SELECT COUNT(*) FROM ndistinct GROUP BY a, b;

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