Rewrite the planner's handling of materialized plan types so that there is

an explicit model of rescan costs being different from first-time costs.
The costing of Material nodes in particular now has some visible relationship
to the actual runtime behavior, where before it was essentially fantasy.
This also fixes up a couple of places where different materialized plan types
were treated differently for no very good reason (probably just oversights).

A couple of the regression tests are affected, because the planner now chooses
to put the other relation on the inside of a nestloop-with-materialize.
So far as I can see both changes are sane, and the planner is now more
consistently following the expectation that it should prefer to materialize
the smaller of two relations.

Per a recent discussion with Robert Haas.

src/backend/executor/execAmi.c

@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- *	$PostgreSQL: pgsql/src/backend/executor/execAmi.c,v 1.103 2009/01/01 17:23:41 momjian Exp $
+ *	$PostgreSQL: pgsql/src/backend/executor/execAmi.c,v 1.104 2009/09/12 22:12:03 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -496,3 +496,30 @@ IndexSupportsBackwardScan(Oid indexid)
 
 	return result;
 }
+
+/*
+ * ExecMaterializesOutput - does a plan type materialize its output?
+ *
+ * Returns true if the plan node type is one that automatically materializes
+ * its output (typically by keeping it in a tuplestore).  For such plans,
+ * a rescan without any parameter change will have zero startup cost and
+ * very low per-tuple cost.
+ */
+bool
+ExecMaterializesOutput(NodeTag plantype)
+{
+	switch (plantype)
+	{
+		case T_Material:
+		case T_FunctionScan:
+		case T_CteScan:
+		case T_WorkTableScan:
+		case T_Sort:
+			return true;
+
+		default:
+			break;
+	}
+
+	return false;
+}

src/backend/optimizer/path/joinpath.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/path/joinpath.c,v 1.122 2009/06/11 14:48:59 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/path/joinpath.c,v 1.123 2009/09/12 22:12:04 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -16,6 +16,7 @@
 
 #include <math.h>
 
+#include "executor/executor.h"
 #include "optimizer/cost.h"
 #include "optimizer/pathnode.h"
 #include "optimizer/paths.h"
@@ -405,18 +406,10 @@ match_unsorted_outer(PlannerInfo *root,
 	else if (nestjoinOK)
 	{
 		/*
-		 * If the cheapest inner path is a join or seqscan, we should consider
-		 * materializing it.  (This is a heuristic: we could consider it
-		 * always, but for inner indexscans it's probably a waste of time.)
-		 * Also skip it if the inner path materializes its output anyway.
+		 * Consider materializing the cheapest inner path, unless it is one
+		 * that materializes its output anyway.
 		 */
-		if (!(inner_cheapest_total->pathtype == T_IndexScan ||
-			  inner_cheapest_total->pathtype == T_BitmapHeapScan ||
-			  inner_cheapest_total->pathtype == T_TidScan ||
-			  inner_cheapest_total->pathtype == T_Material ||
-			  inner_cheapest_total->pathtype == T_FunctionScan ||
-			  inner_cheapest_total->pathtype == T_CteScan ||
-			  inner_cheapest_total->pathtype == T_WorkTableScan))
+		if (!ExecMaterializesOutput(inner_cheapest_total->pathtype))
 			matpath = (Path *)
 				create_material_path(innerrel, inner_cheapest_total);
 

src/backend/optimizer/plan/createplan.c

@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/createplan.c,v 1.261 2009/07/17 23:19:34 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/createplan.c,v 1.262 2009/09/12 22:12:04 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -3266,6 +3266,7 @@ materialize_finished_plan(Plan *subplan)
 
 	/* Set cost data */
 	cost_material(&matpath,
+				  subplan->startup_cost,
 				  subplan->total_cost,
 				  subplan->plan_rows,
 				  subplan->plan_width);

src/backend/optimizer/plan/subselect.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/subselect.c,v 1.152 2009/07/16 06:33:43 petere Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/subselect.c,v 1.153 2009/09/12 22:12:04 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -15,6 +15,7 @@
 
 #include "catalog/pg_operator.h"
 #include "catalog/pg_type.h"
+#include "executor/executor.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
 #include "nodes/nodeFuncs.h"
@@ -564,33 +565,16 @@ build_subplan(PlannerInfo *root, Plan *plan, List *rtable,
 			splan->useHashTable = true;
 
 		/*
-		 * Otherwise, we have the option to tack a MATERIAL node onto the top
+		 * Otherwise, we have the option to tack a Material node onto the top
 		 * of the subplan, to reduce the cost of reading it repeatedly.  This
 		 * is pointless for a direct-correlated subplan, since we'd have to
 		 * recompute its results each time anyway.	For uncorrelated/undirect
-		 * correlated subplans, we add MATERIAL unless the subplan's top plan
+		 * correlated subplans, we add Material unless the subplan's top plan
 		 * node would materialize its output anyway.
 		 */
-		else if (splan->parParam == NIL)
-		{
-			bool		use_material;
-
-			switch (nodeTag(plan))
-			{
-				case T_Material:
-				case T_FunctionScan:
-				case T_CteScan:
-				case T_WorkTableScan:
-				case T_Sort:
-					use_material = false;
-					break;
-				default:
-					use_material = true;
-					break;
-			}
-			if (use_material)
-				plan = materialize_finished_plan(plan);
-		}
+		else if (splan->parParam == NIL &&
+				 !ExecMaterializesOutput(nodeTag(plan)))
+			plan = materialize_finished_plan(plan);
 
 		result = (Node *) splan;
 		isInitPlan = false;

src/backend/optimizer/util/pathnode.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/util/pathnode.c,v 1.152 2009/06/11 14:48:59 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/util/pathnode.c,v 1.153 2009/09/12 22:12:04 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -711,6 +711,7 @@ create_material_path(RelOptInfo *rel, Path *subpath)
 	pathnode->subpath = subpath;
 
 	cost_material(&pathnode->path,
+				  subpath->startup_cost,
 				  subpath->total_cost,
 				  rel->rows,
 				  rel->width);
@@ -1424,7 +1425,8 @@ create_mergejoin_path(PlannerInfo *root,
 		 * cost_mergejoin will avoid choosing anyway).	Therefore
 		 * cost_material's cost estimate is bogus and we should charge just
 		 * cpu_tuple_cost per tuple.  (Keep this estimate in sync with similar
-		 * ones in cost_mergejoin and create_mergejoin_plan.)
+		 * ones in cost_mergejoin and create_mergejoin_plan; also see
+		 * cost_rescan.)
 		 */
 		mpath->startup_cost = inner_path->startup_cost;
 		mpath->total_cost = inner_path->total_cost;

src/include/executor/executor.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/executor/executor.h,v 1.158 2009/07/29 20:56:20 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/executor/executor.h,v 1.159 2009/09/12 22:12:04 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -83,6 +83,7 @@ extern void ExecMarkPos(PlanState *node);
 extern void ExecRestrPos(PlanState *node);
 extern bool ExecSupportsMarkRestore(NodeTag plantype);
 extern bool ExecSupportsBackwardScan(Plan *node);
+extern bool ExecMaterializesOutput(NodeTag plantype);
 
 /*
  * prototypes from functions in execCurrent.c

src/include/optimizer/cost.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/optimizer/cost.h,v 1.97 2009/06/11 14:49:11 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/optimizer/cost.h,v 1.98 2009/09/12 22:12:04 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -86,7 +86,8 @@ extern void cost_sort(Path *path, PlannerInfo *root,
 		  double limit_tuples);
 extern bool sort_exceeds_work_mem(Sort *sort);
 extern void cost_material(Path *path,
-			  Cost input_cost, double tuples, int width);
+			  Cost input_startup_cost, Cost input_total_cost,
+			  double tuples, int width);
 extern void cost_agg(Path *path, PlannerInfo *root,
 		 AggStrategy aggstrategy, int numAggs,
 		 int numGroupCols, double numGroups,

src/test/regress/expected/geometry.out

@@ -260,24 +260,24 @@ SELECT '' AS twenty, b.f1 / p.f1 AS rotation
  twenty |                               rotation                               
 --------+----------------------------------------------------------------------
         | (0,-0),(-0.2,-0.2)
-        | (-0.1,-0.1),(-0.3,-0.3)
-        | (-0.25,-0.25),(-0.25,-0.35)
-        | (-0.3,-0.3),(-0.3,-0.3)
         | (0.08,-0),(0,-0.56)
-        | (0.12,-0.28),(0.04,-0.84)
-        | (0.26,-0.7),(0.1,-0.82)
-        | (0.12,-0.84),(0.12,-0.84)
         | (0.0651176557644,0),(0,-0.0483449262493)
-        | (0.0976764836466,-0.0241724631247),(0.0325588278822,-0.072517389374)
-        | (0.109762715209,-0.0562379754329),(0.0813970697055,-0.0604311578117)
-        | (0.0976764836466,-0.072517389374),(0.0976764836466,-0.072517389374)
         | (-0,0.0828402366864),(-0.201183431953,0)
-        | (-0.100591715976,0.12426035503),(-0.301775147929,0.0414201183432)
-        | (-0.251479289941,0.103550295858),(-0.322485207101,0.0739644970414)
-        | (-0.301775147929,0.12426035503),(-0.301775147929,0.12426035503)
         | (0.2,0),(0,0)
+        | (-0.1,-0.1),(-0.3,-0.3)
+        | (0.12,-0.28),(0.04,-0.84)
+        | (0.0976764836466,-0.0241724631247),(0.0325588278822,-0.072517389374)
+        | (-0.100591715976,0.12426035503),(-0.301775147929,0.0414201183432)
         | (0.3,0),(0.1,0)
+        | (-0.25,-0.25),(-0.25,-0.35)
+        | (0.26,-0.7),(0.1,-0.82)
+        | (0.109762715209,-0.0562379754329),(0.0813970697055,-0.0604311578117)
+        | (-0.251479289941,0.103550295858),(-0.322485207101,0.0739644970414)
         | (0.3,0.05),(0.25,0)
+        | (-0.3,-0.3),(-0.3,-0.3)
+        | (0.12,-0.84),(0.12,-0.84)
+        | (0.0976764836466,-0.072517389374),(0.0976764836466,-0.072517389374)
+        | (-0.301775147929,0.12426035503),(-0.301775147929,0.12426035503)
         | (0.3,0),(0.3,0)
 (20 rows)
 

src/test/regress/expected/geometry_1.out

@@ -260,24 +260,24 @@ SELECT '' AS twenty, b.f1 / p.f1 AS rotation
  twenty |                               rotation                               
 --------+----------------------------------------------------------------------
         | (0,0),(-0.2,-0.2)
-        | (-0.1,-0.1),(-0.3,-0.3)
-        | (-0.25,-0.25),(-0.25,-0.35)
-        | (-0.3,-0.3),(-0.3,-0.3)
         | (0.08,0),(0,-0.56)
-        | (0.12,-0.28),(0.04,-0.84)
-        | (0.26,-0.7),(0.1,-0.82)
-        | (0.12,-0.84),(0.12,-0.84)
         | (0.0651176557644,0),(0,-0.0483449262493)
-        | (0.0976764836466,-0.0241724631247),(0.0325588278822,-0.072517389374)
-        | (0.109762715209,-0.0562379754329),(0.0813970697055,-0.0604311578117)
-        | (0.0976764836466,-0.072517389374),(0.0976764836466,-0.072517389374)
         | (0,0.0828402366864),(-0.201183431953,0)
-        | (-0.100591715976,0.12426035503),(-0.301775147929,0.0414201183432)
-        | (-0.251479289941,0.103550295858),(-0.322485207101,0.0739644970414)
-        | (-0.301775147929,0.12426035503),(-0.301775147929,0.12426035503)
         | (0.2,0),(0,0)
+        | (-0.1,-0.1),(-0.3,-0.3)
+        | (0.12,-0.28),(0.04,-0.84)
+        | (0.0976764836466,-0.0241724631247),(0.0325588278822,-0.072517389374)
+        | (-0.100591715976,0.12426035503),(-0.301775147929,0.0414201183432)
         | (0.3,0),(0.1,0)
+        | (-0.25,-0.25),(-0.25,-0.35)
+        | (0.26,-0.7),(0.1,-0.82)
+        | (0.109762715209,-0.0562379754329),(0.0813970697055,-0.0604311578117)
+        | (-0.251479289941,0.103550295858),(-0.322485207101,0.0739644970414)
         | (0.3,0.05),(0.25,0)
+        | (-0.3,-0.3),(-0.3,-0.3)
+        | (0.12,-0.84),(0.12,-0.84)
+        | (0.0976764836466,-0.072517389374),(0.0976764836466,-0.072517389374)
+        | (-0.301775147929,0.12426035503),(-0.301775147929,0.12426035503)
         | (0.3,0),(0.3,0)
 (20 rows)
 

src/test/regress/expected/geometry_2.out

@@ -260,24 +260,24 @@ SELECT '' AS twenty, b.f1 / p.f1 AS rotation
  twenty |                               rotation                               
 --------+----------------------------------------------------------------------
         | (0,-0),(-0.2,-0.2)
-        | (-0.1,-0.1),(-0.3,-0.3)
-        | (-0.25,-0.25),(-0.25,-0.35)
-        | (-0.3,-0.3),(-0.3,-0.3)
         | (0.08,-0),(0,-0.56)
-        | (0.12,-0.28),(0.04,-0.84)
-        | (0.26,-0.7),(0.1,-0.82)
-        | (0.12,-0.84),(0.12,-0.84)
         | (0.0651176557644,0),(0,-0.0483449262493)
-        | (0.0976764836466,-0.0241724631247),(0.0325588278822,-0.072517389374)
-        | (0.109762715209,-0.0562379754329),(0.0813970697055,-0.0604311578117)
-        | (0.0976764836466,-0.072517389374),(0.0976764836466,-0.072517389374)
         | (-0,0.0828402366864),(-0.201183431953,0)
-        | (-0.100591715976,0.12426035503),(-0.301775147929,0.0414201183432)
-        | (-0.251479289941,0.103550295858),(-0.322485207101,0.0739644970414)
-        | (-0.301775147929,0.12426035503),(-0.301775147929,0.12426035503)
         | (0.2,0),(0,0)
+        | (-0.1,-0.1),(-0.3,-0.3)
+        | (0.12,-0.28),(0.04,-0.84)
+        | (0.0976764836466,-0.0241724631247),(0.0325588278822,-0.072517389374)
+        | (-0.100591715976,0.12426035503),(-0.301775147929,0.0414201183432)
         | (0.3,0),(0.1,0)
+        | (-0.25,-0.25),(-0.25,-0.35)
+        | (0.26,-0.7),(0.1,-0.82)
+        | (0.109762715209,-0.0562379754329),(0.0813970697055,-0.0604311578117)
+        | (-0.251479289941,0.103550295858),(-0.322485207101,0.0739644970414)
         | (0.3,0.05),(0.25,0)
+        | (-0.3,-0.3),(-0.3,-0.3)
+        | (0.12,-0.84),(0.12,-0.84)
+        | (0.0976764836466,-0.072517389374),(0.0976764836466,-0.072517389374)
+        | (-0.301775147929,0.12426035503),(-0.301775147929,0.12426035503)
         | (0.3,0),(0.3,0)
 (20 rows)