Fix handling of opclauses in extended statistics

We expect opclauses to have exactly one Var and one Const, but the code
was checking the Const by calling is_pseudo_constant_clause() which is
incorrect - we need a proper constant.

Fixed by using plain IsA(x,Const) to check type of the node. We need to
do these checks in two places, so move it into a separate function that
can be called in both places.

Reported by Andreas Seltenreich, based on crash reported by sqlsmith.

Backpatch to v12, where this code was introduced.

Discussion: https://postgr.es/m/8736jdhbhc.fsf%40ansel.ydns.eu
Backpatch-to: 12

diff --git a/src/backend/statistics/extended_stats.c b/src/backend/statistics/extended_stats.c
index c56ed48270662b22659a97ee7384162b253f5f44..d2346cbe02e408b367a1611d85d9c53054b07ced 100644 (file)
--- a/src/backend/statistics/extended_stats.c
+++ b/src/backend/statistics/extended_stats.c
@@ -796,21 +796,13 @@ statext_is_compatible_clause_internal(PlannerInfo *root, Node *clause,
        RangeTblEntry *rte = root->simple_rte_array[relid];
        OpExpr     *expr = (OpExpr *) clause;
        Var        *var;
-       bool        varonleft = true;
-       bool        ok;
 
        /* Only expressions with two arguments are considered compatible. */
        if (list_length(expr->args) != 2)
            return false;
 
-       /* see if it actually has the right shape (one Var, one Const) */
-       ok = (NumRelids((Node *) expr) == 1) &&
-           (is_pseudo_constant_clause(lsecond(expr->args)) ||
-            (varonleft = false,
-             is_pseudo_constant_clause(linitial(expr->args))));
-
-       /* unsupported structure (two variables or so) */
-       if (!ok)
+       /* Check if the expression the right shape (one Var, one Const) */
+       if (!examine_opclause_expression(expr, &var, NULL, NULL))
            return false;
 
        /*
@@ -850,8 +842,6 @@ statext_is_compatible_clause_internal(PlannerInfo *root, Node *clause,
            !get_func_leakproof(get_opcode(expr->opno)))
            return false;
 
-       var = (varonleft) ? linitial(expr->args) : lsecond(expr->args);
-
        return statext_is_compatible_clause_internal(root, (Node *) var,
                                                     relid, attnums);
    }
@@ -1196,3 +1186,65 @@ statext_clauselist_selectivity(PlannerInfo *root, List *clauses, int varRelid,
 
    return sel;
 }
+
+/*
+ * examine_operator_expression
+ *     Split expression into Var and Const parts.
+ *
+ * Attempts to match the arguments to either (Var op Const) or (Const op Var),
+ * possibly with a RelabelType on top. When the expression matches this form,
+ * returns true, otherwise returns false.
+ *
+ * Optionally returns pointers to the extracted Var/Const nodes, when passed
+ * non-null pointers (varp, cstp and isgtp). The isgt flag specifies whether
+ * the Var node is on the left (false) or right (true) side of the operator.
+ */
+bool
+examine_opclause_expression(OpExpr *expr, Var **varp, Const **cstp, bool *isgtp)
+{
+   Var    *var;
+   Const  *cst;
+   bool    isgt;
+   Node   *leftop,
+          *rightop;
+
+   /* enforced by statext_is_compatible_clause_internal */
+   Assert(list_length(expr->args) == 2);
+
+   leftop = linitial(expr->args);
+   rightop = lsecond(expr->args);
+
+   /* strip RelabelType from either side of the expression */
+   if (IsA(leftop, RelabelType))
+       leftop = (Node *) ((RelabelType *) leftop)->arg;
+
+   if (IsA(rightop, RelabelType))
+       rightop = (Node *) ((RelabelType *) rightop)->arg;
+
+   if (IsA(leftop, Var) && IsA(rightop, Const))
+   {
+       var = (Var *) leftop;
+       cst = (Const *) rightop;
+       isgt = false;
+   }
+   else if (IsA(leftop, Const) && IsA(rightop, Var))
+   {
+       var = (Var *) rightop;
+       cst = (Const *) leftop;
+       isgt = true;
+   }
+   else
+       return false;
+
+   /* return pointers to the extracted parts if requested */
+   if (varp)
+       *varp = var;
+
+   if (cstp)
+       *cstp = cst;
+
+   if (isgtp)
+       *isgtp = isgt;
+
+   return true;
+}

diff --git a/src/backend/statistics/mcv.c b/src/backend/statistics/mcv.c
index e62421dfa881230a72fd43593ecd3a162836f280..a708a8f6740c4a0b6d9dbf0bdee042b965f52fa8 100644 (file)
--- a/src/backend/statistics/mcv.c
+++ b/src/backend/statistics/mcv.c
@@ -1561,36 +1561,23 @@ mcv_get_match_bitmap(PlannerInfo *root, List *clauses,
        if (is_opclause(clause))
        {
            OpExpr     *expr = (OpExpr *) clause;
-           bool        varonleft = true;
-           bool        ok;
            FmgrInfo    opproc;
 
            /* get procedure computing operator selectivity */
            RegProcedure oprrest = get_oprrest(expr->opno);
 
-           fmgr_info(get_opcode(expr->opno), &opproc);
+           /* valid only after examine_opclause_expression returns true */
+           Var        *var;
+           Const      *cst;
+           bool        isgt;
 
-           ok = (NumRelids(clause) == 1) &&
-               (is_pseudo_constant_clause(lsecond(expr->args)) ||
-                (varonleft = false,
-                 is_pseudo_constant_clause(linitial(expr->args))));
+           fmgr_info(get_opcode(expr->opno), &opproc);
 
-           if (ok)
+           /* extract the var and const from the expression */
+           if (examine_opclause_expression(expr, &var, &cst, &isgt))
            {
-               Var        *var;
-               Const      *cst;
-               bool        isgt;
                int         idx;
 
-               /* extract the var and const from the expression */
-               var = (varonleft) ? linitial(expr->args) : lsecond(expr->args);
-               cst = (varonleft) ? lsecond(expr->args) : linitial(expr->args);
-               isgt = (!varonleft);
-
-               /* strip binary-compatible relabeling */
-               if (IsA(var, RelabelType))
-                   var = (Var *) ((RelabelType *) var)->arg;
-
                /* match the attribute to a dimension of the statistic */
                idx = bms_member_index(keys, var->varattno);
 

diff --git a/src/include/statistics/extended_stats_internal.h b/src/include/statistics/extended_stats_internal.h
index 8fc541993fac9b6785dd4e1d42ca5af4af614b5e..c7f01d4edc7029b8bc7a0d53de758de911da3c66 100644 (file)
--- a/src/include/statistics/extended_stats_internal.h
+++ b/src/include/statistics/extended_stats_internal.h
@@ -97,6 +97,8 @@ extern SortItem *build_sorted_items(int numrows, int *nitems, HeapTuple *rows,
                                    TupleDesc tdesc, MultiSortSupport mss,
                                    int numattrs, AttrNumber *attnums);
 
+extern bool examine_opclause_expression(OpExpr *expr, Var **varp,
+                                       Const **cstp, bool *isgtp);
 
 extern Selectivity mcv_clauselist_selectivity(PlannerInfo *root,
                                              StatisticExtInfo *stat,