Apply a MATERIAL node to the result of an uncorrelated subplan, if it

looks like it will save computation to do so.

diff --git a/src/backend/optimizer/plan/subselect.c b/src/backend/optimizer/plan/subselect.c
index 2790b2740b69ba1f5e0280cba6e4bb375f25db61..eea5b332cfebeef9711fd13faf8f195f0dff971c 100644 (file)
--- a/src/backend/optimizer/plan/subselect.c
+++ b/src/backend/optimizer/plan/subselect.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *   $Header: /cvsroot/pgsql/src/backend/optimizer/plan/subselect.c,v 1.28 2000/02/15 20:49:18 tgl Exp $
+ *   $Header: /cvsroot/pgsql/src/backend/optimizer/plan/subselect.c,v 1.29 2000/03/02 04:08:16 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -18,6 +18,8 @@
 #include "nodes/makefuncs.h"
 #include "nodes/nodeFuncs.h"
 #include "optimizer/clauses.h"
+#include "optimizer/cost.h"
+#include "optimizer/planmain.h"
 #include "optimizer/planner.h"
 #include "optimizer/subselect.h"
 #include "parser/parse_expr.h"
@@ -123,6 +125,7 @@ static Node *
 make_subplan(SubLink *slink)
 {
    SubPlan    *node = makeNode(SubPlan);
+   Query      *subquery = (Query *) (slink->subselect);
    double      tuple_fraction;
    Plan       *plan;
    List       *lst;
@@ -151,8 +154,7 @@ make_subplan(SubLink *slink)
    else
        tuple_fraction = 0.5;   /* 50% */
 
-   node->plan = plan = union_planner((Query *) slink->subselect,
-                                     tuple_fraction);
+   node->plan = plan = union_planner(subquery, tuple_fraction);
 
    /*
     * Assign subPlan, extParam and locParam to plan nodes. At the moment,
@@ -179,7 +181,7 @@ make_subplan(SubLink *slink)
    PlannerQueryLevel--;
 
    node->plan_id = PlannerPlanId++;
-   node->rtable = ((Query *) slink->subselect)->rtable;
+   node->rtable = subquery->rtable;
    node->sublink = slink;
    slink->subselect = NULL;    /* cool ?! */
 
@@ -287,12 +289,76 @@ make_subplan(SubLink *slink)
    }
    else
    {
-       /* make expression of SUBPLAN type */
        Expr       *expr = makeNode(Expr);
        List       *args = NIL;
        List       *newoper = NIL;
        int         i = 0;
 
+       /*
+        * We can't convert subplans of ALL_SUBLINK or ANY_SUBLINK types to
+        * initPlans, even when they are uncorrelated or undirect correlated,
+        * because we need to scan the output of the subplan for each outer
+        * tuple.  However, we have the option to tack a MATERIAL node onto
+        * the top of an uncorrelated/undirect correlated subplan, which lets
+        * us do the work of evaluating the subplan only once.  We do this
+        * if the subplan's top plan node is anything more complicated than
+        * a sequential or index scan, and we do it even for those plan types
+        * if the qual appears selective enough to eliminate many tuples.
+        */
+       if (node->parParam == NIL)
+       {
+           bool        use_material;
+
+           switch (nodeTag(plan))
+           {
+               case T_SeqScan:
+               {
+                   Selectivity qualsel;
+
+                   qualsel = clauselist_selectivity(subquery, plan->qual, 0);
+                   /* Is 10% selectivity a good threshold?? */
+                   use_material = qualsel < 0.10;
+                   break;
+               }
+               case T_IndexScan:
+               {
+                   List       *indxqual = ((IndexScan *) plan)->indxqualorig;
+                   Selectivity qualsel;
+
+                   qualsel = clauselist_selectivity(subquery, plan->qual, 0);
+                   qualsel *= clauselist_selectivity(subquery, indxqual, 0);
+                   /* Note: if index is lossy, we just double-counted the
+                    * index selectivity.  Worth fixing?
+                    */
+                   /* Is 10% selectivity a good threshold?? */
+                   use_material = qualsel < 0.10;
+                   break;
+               }
+               case T_Material:
+               case T_Sort:
+                   /* Don't add another Material node if there's one already,
+                    * nor if the top node is a Sort, since Sort materializes
+                    * its output anyway.  (I doubt either case can happen in
+                    * practice for a subplan, but...)
+                    */
+                   use_material = false;
+                   break;
+               default:
+                   use_material = true;
+                   break;
+           }
+           if (use_material)
+           {
+               plan = (Plan *) make_noname(plan->targetlist,
+                                           NIL,
+                                           plan);
+               node->plan = plan;
+           }
+       }
+
+       /*
+        * Make expression of SUBPLAN type
+        */
        expr->typeOid = BOOLOID; /* bogus, but we don't really care */
        expr->opType = SUBPLAN_EXPR;
        expr->oper = (Node *) node;