rdelaage
/
postgresql
mirror of https://git.postgresql.org/git/postgresql.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

Fix ndistinct estimates with system attributes 

When estimating the number of groups using extended statistics, the code
was discarding information about system attributes. This led to strange
situation that

    SELECT 1 FROM t GROUP BY ctid;

could have produced higher estimate (equal to pg_class.reltuples) than

    SELECT 1 FROM t GROUP BY a, b, ctid;

with extended statistics on (a,b). Fixed by retaining information about
the system attribute.

Backpatch all the way to 10, where extended statistics were introduced.

Author: Tomas Vondra
Backpatch-through: 10
This commit is contained in:
Tomas Vondra 2021-03-26 22:34:53 +01:00
parent 83ba02c83e
commit 2a307df1bb
1 changed files with 3 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
src/backend/utils/adt/selfuncs.c
View File

@ -4025,11 +4025,11 @@ estimate_multivariate_ndistinct(PlannerInfo *root, RelOptInfo *rel,
attnum = ((Var *) varinfo->var)->varattno;
if (!AttrNumberIsForUserDefinedAttr(attnum))
if (AttrNumberIsForUserDefinedAttr(attnum) &&
bms_is_member(attnum, matched))
continue;
if (!bms_is_member(attnum, matched))
newlist = lappend(newlist, varinfo);
newlist = lappend(newlist, varinfo);
}
*varinfos = newlist;