From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Fri, 13 Dec 2002 17:29:25 +0000 (+0000)
Subject: Adjust costsize calculations to avoid introducing unnecessary roundoff
X-Git-Tag: REL7_4_BETA1~1369
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=77b7a740f95250af7d78f69e9c906c3e53f32e7b;p=postgresql

Adjust costsize calculations to avoid introducing unnecessary roundoff
error.  This seems to explain the differing choice of plan that's been
causing geometry regress test to fail for the last few days.
---

diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index 2125ff034f..114e879885 100644
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -42,7 +42,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.94 2002/12/12 15:49:28 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.95 2002/12/13 17:29:25 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -672,12 +672,22 @@ cost_nestloop(Path *path, Query *root,
 	 */
 	startup_cost += outer_path->startup_cost + inner_path->startup_cost;
 	run_cost += outer_path->total_cost - outer_path->startup_cost;
-	run_cost += outer_path->parent->rows *
-		(inner_path->total_cost - inner_path->startup_cost);
-	if (!(IsA(inner_path, MaterialPath) ||
-		  IsA(inner_path, HashPath)) &&
-		outer_path->parent->rows > 1)
-		run_cost += (outer_path->parent->rows - 1) * inner_path->startup_cost;
+	if (IsA(inner_path, MaterialPath) ||
+		IsA(inner_path, HashPath))
+	{
+		/* charge only run cost for each iteration of inner path */
+		run_cost += outer_path->parent->rows *
+			(inner_path->total_cost - inner_path->startup_cost);
+	}
+	else
+	{
+		/*
+		 * charge total cost for each iteration of inner path, except we
+		 * already charged the first startup_cost in our own startup
+		 */
+		run_cost += outer_path->parent->rows * inner_path->total_cost
+			- inner_path->startup_cost;
+	}
 
 	/*
 	 * Number of tuples processed (not number emitted!).  If inner path is
@@ -768,8 +778,8 @@ cost_mergejoin(Path *path, Query *root,
 		innerscansel = firstclause->left_mergescansel;
 	}
 
-	outer_rows = outer_path->parent->rows * outerscansel;
-	inner_rows = inner_path->parent->rows * innerscansel;
+	outer_rows = ceil(outer_path->parent->rows * outerscansel);
+	inner_rows = ceil(inner_path->parent->rows * innerscansel);
 
 	/* cost of source data */
 
@@ -1343,10 +1353,12 @@ approx_selectivity(Query *root, List *quals)
 void
 set_baserel_size_estimates(Query *root, RelOptInfo *rel)
 {
+	double		temp;
+
 	/* Should only be applied to base relations */
 	Assert(length(rel->relids) == 1);
 
-	rel->rows = rel->tuples *
+	temp = rel->tuples *
 		restrictlist_selectivity(root,
 								 rel->baserestrictinfo,
 								 lfirsti(rel->relids));
@@ -1354,10 +1366,14 @@ set_baserel_size_estimates(Query *root, RelOptInfo *rel)
 	/*
 	 * Force estimate to be at least one row, to make explain output look
 	 * better and to avoid possible divide-by-zero when interpolating
-	 * cost.
+	 * cost.  Make it an integer, too.
 	 */
-	if (rel->rows < 1.0)
-		rel->rows = 1.0;
+	if (temp < 1.0)
+		temp = 1.0;
+	else
+		temp = ceil(temp);
+
+	rel->rows = temp;
 
 	rel->baserestrictcost = cost_qual_eval(rel->baserestrictinfo);
 
@@ -1437,10 +1453,12 @@ set_joinrel_size_estimates(Query *root, RelOptInfo *rel,
 	/*
 	 * Force estimate to be at least one row, to make explain output look
 	 * better and to avoid possible divide-by-zero when interpolating
-	 * cost.
+	 * cost.  Make it an integer, too.
 	 */
 	if (temp < 1.0)
 		temp = 1.0;
+	else
+		temp = ceil(temp);
 
 	rel->rows = temp;
 
@@ -1470,6 +1488,8 @@ set_joinrel_size_estimates(Query *root, RelOptInfo *rel,
 void
 set_function_size_estimates(Query *root, RelOptInfo *rel)
 {
+	double		temp;
+
 	/* Should only be applied to base relations that are functions */
 	Assert(length(rel->relids) == 1);
 	Assert(rel->rtekind == RTE_FUNCTION);
@@ -1483,7 +1503,7 @@ set_function_size_estimates(Query *root, RelOptInfo *rel)
 	rel->tuples = 1000;
 
 	/* Now estimate number of output rows */
-	rel->rows = rel->tuples *
+	temp = rel->tuples *
 		restrictlist_selectivity(root,
 								 rel->baserestrictinfo,
 								 lfirsti(rel->relids));
@@ -1491,10 +1511,14 @@ set_function_size_estimates(Query *root, RelOptInfo *rel)
 	/*
 	 * Force estimate to be at least one row, to make explain output look
 	 * better and to avoid possible divide-by-zero when interpolating
-	 * cost.
+	 * cost.  Make it an integer, too.
 	 */
-	if (rel->rows < 1.0)
-		rel->rows = 1.0;
+	if (temp < 1.0)
+		temp = 1.0;
+	else
+		temp = ceil(temp);
+
+	rel->rows = temp;
 
 	rel->baserestrictcost = cost_qual_eval(rel->baserestrictinfo);