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, 16 insertions, 23 deletions

diff --git a/src/backend/optimizer/path/tidpath.c b/src/backend/optimizer/path/tidpath.c
index ab0427ef322..1e7dc43473b 100644
--- a/src/backend/optimizer/path/tidpath.c
+++ b/src/backend/optimizer/path/tidpath.c
@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/path/tidpath.c,v 1.4 2000/02/07 04:40:59 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/path/tidpath.c,v 1.5 2000/02/15 20:49:17 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -36,7 +36,7 @@
 #include "parser/parsetree.h"
 #include "utils/lsyscache.h"
 
-static List	*create_tidscan_joinpaths(RelOptInfo *);
+static void create_tidscan_joinpaths(RelOptInfo *rel);
 static List	*TidqualFromRestrictinfo(List *relids, List *restrictinfo);
 static bool	isEvaluable(int varno, Node *node);
 static Node	*TidequalClause(int varno, Expr *node);
@@ -234,61 +234,54 @@ TidqualFromRestrictinfo(List *relids, List *restrictinfo)
 
 /*
  * create_tidscan_joinpaths
- *	  Creates a path corresponding to a tid_direct scan, returning the
- *	  pathnode.
+ *	  Create innerjoin paths if there are suitable joinclauses.
  *
+ * XXX does this actually work?
  */
-List *
+static void
 create_tidscan_joinpaths(RelOptInfo *rel)
 {
 	List		*rlst = NIL,
 				*lst;
-	TidPath		*pathnode = (TidPath *) NULL;
-	List		*restinfo,
-				*tideval;
 
 	foreach (lst, rel->joininfo)
 	{
-		JoinInfo   *joininfo = (JoinInfo *)lfirst(lst);
+		JoinInfo   *joininfo = (JoinInfo *) lfirst(lst);
+		List		*restinfo,
+					*tideval;
 
 		restinfo = joininfo->jinfo_restrictinfo;
 		tideval = TidqualFromRestrictinfo(rel->relids, restinfo);
 		if (length(tideval) == 1)
 		{
-			pathnode = makeNode(TidPath);
+			TidPath		*pathnode = makeNode(TidPath);
 
 			pathnode->path.pathtype = T_TidScan;
 			pathnode->path.parent = rel;
 			pathnode->path.pathkeys = NIL;
-			pathnode->path.path_cost = cost_tidscan(rel, tideval);
 			pathnode->tideval = tideval;
 			pathnode->unjoined_relids = joininfo->unjoined_relids;
+
+			cost_tidscan(&pathnode->path, rel, tideval);
+
 			rlst = lappend(rlst, pathnode);
 		}
 	}
 	rel->innerjoin = nconc(rel->innerjoin, rlst);
-	return rlst;
 }
 
 /*
  * create_tidscan_paths
- *	  Creates a path corresponding to a tid direct scan, returning the
- *	  pathnode List.
- *
+ *	  Creates paths corresponding to tid direct scans of the given rel.
+ *	  Candidate paths are added to the rel's pathlist (using add_path).
  */
-List *
+void
 create_tidscan_paths(Query *root, RelOptInfo *rel)
 {
-	List	*rlst = NIL;
-	TidPath	*pathnode = (TidPath *) NULL;
 	List	*tideval = TidqualFromRestrictinfo(rel->relids,
 											   rel->baserestrictinfo);
 	
 	if (tideval)
-		pathnode = create_tidscan_path(rel, tideval);
-	if (pathnode)
-		rlst = lcons(pathnode, rlst);
+		add_path(rel, (Path *) create_tidscan_path(rel, tideval));
 	create_tidscan_joinpaths(rel);
-
-	return rlst;
 }