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

diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index 35a8995f623829e968a3529022068b27cee8f921..024f325eb0206b3e09d9668843a2788a1be8766f 100644 (file)
--- a/src/backend/utils/adt/selfuncs.c
+++ b/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);
+               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 */
@@ -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);
                }

diff --git a/src/test/regress/expected/stats_ext.out b/src/test/regress/expected/stats_ext.out
index b65228fa07accc98250dfba45a224d2620a242d9..dfbc41c390d3decc3a2fa11a9d2bbcc2cb852a71 100644 (file)
--- a/src/test/regress/expected/stats_ext.out
+++ b/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 

diff --git a/src/test/regress/sql/stats_ext.sql b/src/test/regress/sql/stats_ext.sql
index 040ee97a1e51870ae1858292732cbfed6f6148f5..6237fb25c205570f686609dccc41ce3b85b4a9eb 100644 (file)
--- a/src/test/regress/sql/stats_ext.sql
+++ b/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');