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 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;