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, 13 insertions, 27 deletions

diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index 2b152b2fe5b..2a38a349d60 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -5,7 +5,7 @@
  * Portions Copyright (c) 1996-2000, PostgreSQL, Inc
  * Portions Copyright (c) 1994-5, Regents of the University of California
  *
- *	  $Id: explain.c,v 1.53 2000/02/15 03:36:39 thomas Exp $
+ * $Header: /cvsroot/pgsql/src/backend/commands/explain.c,v 1.54 2000/02/15 20:49:08 tgl Exp $
  *
  */
 
@@ -217,39 +217,24 @@ explain_outNode(StringInfo str, Plan *plan, int indent, ExplainState *es)
 			{
 				relation = RelationIdGetRelation(lfirsti(l));
 				Assert(relation);
-				if (++i > 1)
-					appendStringInfo(str, ", ");
-				appendStringInfo(str,
+				appendStringInfo(str, "%s%s",
+								 (++i > 1) ? ", " : "",
 								 stringStringInfo(RelationGetRelationName(relation)));
 				/* drop relcache refcount from RelationIdGetRelation */
 				RelationDecrementReferenceCount(relation);
 			}
+			/* FALL THRU */
 		case T_SeqScan:
+		case T_TidScan:
 			if (((Scan *) plan)->scanrelid > 0)
 			{
 				RangeTblEntry *rte = nth(((Scan *) plan)->scanrelid - 1, es->rtable);
 
-				appendStringInfo(str, " on ");
-				if (strcmp(rte->ref->relname, rte->relname) != 0)
-				{
-					appendStringInfo(str, "%s ",
-									 stringStringInfo(rte->relname));
-				}
-				appendStringInfo(str, stringStringInfo(rte->ref->relname));
-			}
-			break;
-		case T_TidScan:
-			if (((TidScan *) plan)->scan.scanrelid > 0)
-			{
-				RangeTblEntry *rte = nth(((TidScan *) plan)->scan.scanrelid - 1, es->rtable);
-
-				appendStringInfo(str, " on ");
-				if (strcmp(rte->ref->relname, rte->relname) != 0)
-				{
-					appendStringInfo(str, "%s ",
-									 stringStringInfo(rte->relname));
-				}
-				appendStringInfo(str, stringStringInfo(rte->ref->relname));
+				appendStringInfo(str, " on %s",
+								 stringStringInfo(rte->relname));
+				if (rte->ref && strcmp(rte->ref->relname, rte->relname) != 0)
+					appendStringInfo(str, " %s",
+									 stringStringInfo(rte->ref->relname));
 			}
 			break;
 		default:
@@ -257,8 +242,9 @@ explain_outNode(StringInfo str, Plan *plan, int indent, ExplainState *es)
 	}
 	if (es->printCost)
 	{
-		appendStringInfo(str, "  (cost=%.2f rows=%.0f width=%d)",
-						 plan->cost, plan->plan_rows, plan->plan_width);
+		appendStringInfo(str, "  (cost=%.2f..%.2f rows=%.0f width=%d)",
+						 plan->startup_cost, plan->total_cost,
+						 plan->plan_rows, plan->plan_width);
 	}
 	appendStringInfo(str, "\n");