Better solution to the IN-list issue: instead of having an arbitrary cutoff,

treat Var and non-Var IN-list items differently.  Only non-Var items are
candidates to go into an ANY(ARRAY) construct --- we put all Vars as separate
OR conditions on the grounds that that leaves more scope for optimization.
Per suggestion from Robert Haas.

diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
index ced222578db86251b5fd08cf8e1543be1d89f160..b5299d010a617ac75e3295ba64d485ea9743a3fc 100644 (file)
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/parser/parse_expr.c,v 1.236 2008/10/25 17:19:09 tgl Exp $
+ *   $PostgreSQL: pgsql/src/backend/parser/parse_expr.c,v 1.237 2008/10/26 02:46:25 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -939,11 +939,13 @@ transformAExprOf(ParseState *pstate, A_Expr *a)
 static Node *
 transformAExprIn(ParseState *pstate, A_Expr *a)
 {
+   Node       *result = NULL;
    Node       *lexpr;
    List       *rexprs;
+   List       *rvars;
+   List       *rnonvars;
    bool        useOr;
    bool        haveRowExpr;
-   Node       *result;
    ListCell   *l;
 
    /*
@@ -959,41 +961,33 @@ transformAExprIn(ParseState *pstate, A_Expr *a)
     * possible if the inputs are all scalars (no RowExprs) and there is a
     * suitable array type available.  If not, we fall back to a boolean
     * condition tree with multiple copies of the lefthand expression.
+    * Also, any IN-list items that contain Vars are handled as separate
+    * boolean conditions, because that gives the planner more scope for
+    * optimization on such clauses.
     *
     * First step: transform all the inputs, and detect whether any are
-    * RowExprs.
+    * RowExprs or contain Vars.
     */
    lexpr = transformExpr(pstate, a->lexpr);
    haveRowExpr = (lexpr && IsA(lexpr, RowExpr));
-   rexprs = NIL;
+   rexprs = rvars = rnonvars = NIL;
    foreach(l, (List *) a->rexpr)
    {
        Node       *rexpr = transformExpr(pstate, lfirst(l));
 
        haveRowExpr |= (rexpr && IsA(rexpr, RowExpr));
        rexprs = lappend(rexprs, rexpr);
+       if (contain_vars_of_level(rexpr, 0))
+           rvars = lappend(rvars, rexpr);
+       else
+           rnonvars = lappend(rnonvars, rexpr);
    }
 
    /*
-    * We prefer a boolean tree to ScalarArrayOpExpr if any of these are true:
-    *
-    * 1. We have a RowExpr anywhere.
-    *
-    * 2. There's only one righthand expression --- best to just generate a
-    * simple = comparison.
-    *
-    * 3. There's a reasonably small number of righthand expressions and
-    * they contain any Vars.  This is a heuristic to support cases like
-    * WHERE '555-1212' IN (tab.home_phone, tab.work_phone), which can be
-    * optimized into an OR of indexscans on different indexes so long as
-    * it's left as an OR tree.  (It'd be better to leave this decision
-    * to the planner, no doubt, but the amount of code required to reformat
-    * the expression later on seems out of proportion to the benefit.)
+    * ScalarArrayOpExpr is only going to be useful if there's more than
+    * one non-Var righthand item.  Also, it won't work for RowExprs.
     */
-   if (!(haveRowExpr ||
-         list_length(rexprs) == 1 ||
-         (list_length(rexprs) <= 32 &&
-          contain_vars_of_level((Node *) rexprs, 0))))
+   if (!haveRowExpr && list_length(rnonvars) > 1)
    {
        List       *allexprs;
        Oid         scalar_type;
@@ -1004,9 +998,9 @@ transformAExprIn(ParseState *pstate, A_Expr *a)
         * since the LHS' type is first in the list, it will be preferred when
         * there is doubt (eg, when all the RHS items are unknown literals).
         *
-        * Note: use list_concat here not lcons, to avoid damaging rexprs.
+        * Note: use list_concat here not lcons, to avoid damaging rnonvars.
         */
-       allexprs = list_concat(list_make1(lexpr), rexprs);
+       allexprs = list_concat(list_make1(lexpr), rnonvars);
        scalar_type = select_common_type(pstate, allexprs, NULL, NULL);
 
        /* Do we have an array type to use? */
@@ -1017,14 +1011,14 @@ transformAExprIn(ParseState *pstate, A_Expr *a)
        if (array_type != InvalidOid)
        {
            /*
-            * OK: coerce all the right-hand inputs to the common type and
-            * build an ArrayExpr for them.
+            * OK: coerce all the right-hand non-Var inputs to the common type
+            * and build an ArrayExpr for them.
             */
            List       *aexprs;
            ArrayExpr  *newa;
 
            aexprs = NIL;
-           foreach(l, rexprs)
+           foreach(l, rnonvars)
            {
                Node       *rexpr = (Node *) lfirst(l);
 
@@ -1040,19 +1034,21 @@ transformAExprIn(ParseState *pstate, A_Expr *a)
            newa->multidims = false;
            newa->location = -1;
 
-           return (Node *) make_scalar_array_op(pstate,
-                                                a->name,
-                                                useOr,
-                                                lexpr,
-                                                (Node *) newa,
-                                                a->location);
+           result = (Node *) make_scalar_array_op(pstate,
+                                                  a->name,
+                                                  useOr,
+                                                  lexpr,
+                                                  (Node *) newa,
+                                                  a->location);
+
+           /* Consider only the Vars (if any) in the loop below */
+           rexprs = rvars;
        }
    }
 
    /*
     * Must do it the hard way, ie, with a boolean expression tree.
     */
-   result = NULL;
    foreach(l, rexprs)
    {
        Node       *rexpr = (Node *) lfirst(l);