Skip system attributes when applying mvdistinct stats

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

Author: tvondra

src/backend/utils/adt/selfuncs.c

@@ -3582,14 +3582,19 @@ estimate_multivariate_ndistinct(PlannerInfo *root, RelOptInfo *rel,
 foreach(lc, *varinfos)
 {
 GroupVarInfo *varinfo = (GroupVarInfo *) lfirst(lc);
+AttrNumberattnum;
 
 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 */
@@ -3669,6 +3674,10 @@ 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);
 }

src/test/regress/expected/stats_ext.out

@@ -233,6 +233,13 @@ SELECT s.stxkind, d.stxdndistinct
  {d,f,m} | {"3, 4": 11, "3, 6": 11, "4, 6": 11, "3, 4, 6": 11}
 (1 row)
 
+-- minor improvement, make sure the ctid does not break the matching
+SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY ctid, a, b');
+ estimated | actual 
+-----------+--------
+ 11 | 1000
+(1 row)
+
 -- Hash Aggregate, thanks to estimates improved by the statistic
 SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b');
  estimated | actual 

src/test/regress/sql/stats_ext.sql

@@ -167,6 +167,9 @@ SELECT s.stxkind, d.stxdndistinct
  WHERE s.stxrelid = 'ndistinct'::regclass
  AND d.stxoid = s.oid;
 
+-- minor improvement, make sure the ctid does not break the matching
+SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY ctid, a, b');
+
 -- Hash Aggregate, thanks to estimates improved by the statistic
 SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b');