New cost model for planning, incorporating a penalty for random page

accesses versus sequential accesses, a (very crude) estimate of the
effects of caching on random page accesses, and cost to evaluate WHERE-
clause expressions.  Export critical parameters for this model as SET
variables.  Also, create SET variables for the planner's enable flags
(enable_seqscan, enable_indexscan, etc) so that these can be controlled
more conveniently than via PGOPTIONS.

Planner now estimates both startup cost (cost before retrieving
first tuple) and total cost of each path, so it can optimize queries
with LIMIT on a reasonable basis by interpolating between these costs.
Same facility is a win for EXISTS(...) subqueries and some other cases.

Redesign pathkey representation to achieve a major speedup in planning
(I saw as much as 5X on a 10-way join); also minor changes in planner
to reduce memory consumption by recycling discarded Path nodes and
not constructing unnecessary lists.

Minor cleanups to display more-plausible costs in some cases in
EXPLAIN output.

Initdb forced by change in interface to index cost estimation
functions.

1 files changed, 31 insertions, 12 deletions

diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index ab41413432c..30106744ded 100644
--- a/src/backend/utils/adt/selfuncs.c
+++ b/src/backend/utils/adt/selfuncs.c
@@ -15,7 +15,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/utils/adt/selfuncs.c,v 1.54 2000/01/26 05:57:14 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/utils/adt/selfuncs.c,v 1.55 2000/02/15 20:49:21 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -756,7 +756,9 @@ getattstatistics(Oid relid,
 static void
 genericcostestimate(Query *root, RelOptInfo *rel,
 					IndexOptInfo *index, List *indexQuals,
-					Cost *indexAccessCost, Selectivity *indexSelectivity)
+					Cost *indexStartupCost,
+					Cost *indexTotalCost,
+					Selectivity *indexSelectivity)
 {
 	double numIndexTuples;
 	double numIndexPages;
@@ -771,8 +773,17 @@ genericcostestimate(Query *root, RelOptInfo *rel,
 	/* Estimate the number of index pages that will be retrieved */
 	numIndexPages = *indexSelectivity * index->pages;
 
-	/* Compute the index access cost */
-    *indexAccessCost = numIndexPages + cpu_index_page_weight * numIndexTuples;
+	/*
+	 * Compute the index access cost.
+	 *
+	 * Our generic assumption is that the index pages will be read
+	 * sequentially, so they have cost 1.0 each, not random_page_cost.
+	 * Also, we charge for evaluation of the indexquals at each index tuple.
+     * All the costs are assumed to be paid incrementally during the scan.
+     */
+    *indexStartupCost = 0;
+    *indexTotalCost = numIndexPages +
+		(cpu_index_tuple_cost + cost_qual_eval(indexQuals)) * numIndexTuples;
 }
 
 /*
@@ -782,35 +793,43 @@ genericcostestimate(Query *root, RelOptInfo *rel,
 void
 btcostestimate(Query *root, RelOptInfo *rel,
 			   IndexOptInfo *index, List *indexQuals,
-			   Cost *indexAccessCost, Selectivity *indexSelectivity)
+			   Cost *indexStartupCost,
+			   Cost *indexTotalCost,
+			   Selectivity *indexSelectivity)
 {
 	genericcostestimate(root, rel, index, indexQuals,
-						indexAccessCost, indexSelectivity);
+						indexStartupCost, indexTotalCost, indexSelectivity);
 }
 
 void
 rtcostestimate(Query *root, RelOptInfo *rel,
 			   IndexOptInfo *index, List *indexQuals,
-			   Cost *indexAccessCost, Selectivity *indexSelectivity)
+			   Cost *indexStartupCost,
+			   Cost *indexTotalCost,
+			   Selectivity *indexSelectivity)
 {
 	genericcostestimate(root, rel, index, indexQuals,
-						indexAccessCost, indexSelectivity);
+						indexStartupCost, indexTotalCost, indexSelectivity);
 }
 
 void
 hashcostestimate(Query *root, RelOptInfo *rel,
 				 IndexOptInfo *index, List *indexQuals,
-				 Cost *indexAccessCost, Selectivity *indexSelectivity)
+				 Cost *indexStartupCost,
+				 Cost *indexTotalCost,
+				 Selectivity *indexSelectivity)
 {
 	genericcostestimate(root, rel, index, indexQuals,
-						indexAccessCost, indexSelectivity);
+						indexStartupCost, indexTotalCost, indexSelectivity);
 }
 
 void
 gistcostestimate(Query *root, RelOptInfo *rel,
 				 IndexOptInfo *index, List *indexQuals,
-				 Cost *indexAccessCost, Selectivity *indexSelectivity)
+				 Cost *indexStartupCost,
+				 Cost *indexTotalCost,
+				 Selectivity *indexSelectivity)
 {
 	genericcostestimate(root, rel, index, indexQuals,
-						indexAccessCost, indexSelectivity);
+						indexStartupCost, indexTotalCost, indexSelectivity);
 }