postgres.git / summary / log / commit / refs

commit    e5eb40eed470ef98e50787ccefe6d32674437be4
Author:   Tomas Vondra <tomas.vondra@postgresql.org>
Date:     Fri Mar 26 21:34:53 2021 +0000
First released in: 14.0, 10.17, 11.12, 12.7, 13.3

    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


 src/backend/utils/adt/selfuncs.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index e128dccb04b..c2f5f948b06 100644
--- a/src/backend/utils/adt/selfuncs.c
+++ b/src/backend/utils/adt/selfuncs.c
@@ -3851,11 +3851,11 @@ 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;


[parent: d544671f1572]