In cost_mergejoin, the early-exit effect should not apply to the

tglsfdc · tglsfdc · commit 280de290d794 · 2005-04-04T01:43:12.000Z
outer side of an outer join.  Per andrew@supernews.
diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
@@ -49,7 +49,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/path/costsize.c,v 1.140 2005/03/27 23:53:02 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/path/costsize.c,v 1.141 2005/04/04 01:43:12 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -917,16 +917,17 @@ cost_mergejoin(MergePath *path, Query *root)
 	rescanratio = 1.0 + (rescannedtuples / inner_path_rows);
 
 	/*
-	 * A merge join will stop as soon as it exhausts either input stream.
-	 * Estimate fraction of the left and right inputs that will actually
-	 * need to be scanned.	We use only the first (most significant) merge
-	 * clause for this purpose.
+	 * A merge join will stop as soon as it exhausts either input stream
+	 * (unless it's an outer join, in which case the outer side has to be
+	 * scanned all the way anyway).  Estimate fraction of the left and right
+	 * inputs that will actually need to be scanned. We use only the first
+	 * (most significant) merge clause for this purpose.
 	 *
 	 * Since this calculation is somewhat expensive, and will be the same for
 	 * all mergejoin paths associated with the merge clause, we cache the
 	 * results in the RestrictInfo node.
 	 */
-	if (mergeclauses)
+	if (mergeclauses && path->jpath.jointype != JOIN_FULL)
 	{
 		firstclause = (RestrictInfo *) linitial(mergeclauses);
 		if (firstclause->left_mergescansel < 0) /* not computed yet? */
@@ -946,10 +947,14 @@ cost_mergejoin(MergePath *path, Query *root)
 			outerscansel = firstclause->right_mergescansel;
 			innerscansel = firstclause->left_mergescansel;
 		}
+		if (path->jpath.jointype == JOIN_LEFT)
+			outerscansel = 1.0;
+		else if (path->jpath.jointype == JOIN_RIGHT)
+			innerscansel = 1.0;
 	}
 	else
 	{
-		/* cope with clauseless mergejoin */
+		/* cope with clauseless or full mergejoin */
 		outerscansel = innerscansel = 1.0;
 	}
 

Original file line number	Diff line number	Diff line change
`@@ -49,7 +49,7 @@`
`49`	`49`	`* Portions Copyright (c) 1994, Regents of the University of California`
`50`	`50`	`*`
`51`	`51`	`* IDENTIFICATION`
`52`		`- * $PostgreSQL: pgsql/src/backend/optimizer/path/costsize.c,v 1.140 2005/03/27 23:53:02 tgl Exp $`
	`52`	`+ * $PostgreSQL: pgsql/src/backend/optimizer/path/costsize.c,v 1.141 2005/04/04 01:43:12 tgl Exp $`
`53`	`53`	`*`
`54`	`54`	`*-------------------------------------------------------------------------`
`55`	`55`	`*/`
`@@ -917,16 +917,17 @@ cost_mergejoin(MergePath path, Query root)`
`917`	`917`	`rescanratio = 1.0 + (rescannedtuples / inner_path_rows);`
`918`	`918`
`919`	`919`	`/*`
`920`		`- * A merge join will stop as soon as it exhausts either input stream.`
`921`		`- * Estimate fraction of the left and right inputs that will actually`
`922`		`- * need to be scanned. We use only the first (most significant) merge`
`923`		`- * clause for this purpose.`
	`920`	`+ * A merge join will stop as soon as it exhausts either input stream`
	`921`	`+ * (unless it's an outer join, in which case the outer side has to be`
	`922`	`+ * scanned all the way anyway). Estimate fraction of the left and right`
	`923`	`+ * inputs that will actually need to be scanned. We use only the first`
	`924`	`+ * (most significant) merge clause for this purpose.`
`924`	`925`	`*`
`925`	`926`	`* Since this calculation is somewhat expensive, and will be the same for`
`926`	`927`	`* all mergejoin paths associated with the merge clause, we cache the`
`927`	`928`	`* results in the RestrictInfo node.`
`928`	`929`	`*/`
`929`		`- if (mergeclauses)`
	`930`	`+ if (mergeclauses && path->jpath.jointype != JOIN_FULL)`
`930`	`931`	`{`
`931`	`932`	`firstclause = (RestrictInfo *) linitial(mergeclauses);`
`932`	`933`	`if (firstclause->left_mergescansel < 0) /* not computed yet? */`
`@@ -946,10 +947,14 @@ cost_mergejoin(MergePath path, Query root)`
`946`	`947`	`outerscansel = firstclause->right_mergescansel;`
`947`	`948`	`innerscansel = firstclause->left_mergescansel;`
`948`	`949`	`}`
	`950`	`+ if (path->jpath.jointype == JOIN_LEFT)`
	`951`	`+ outerscansel = 1.0;`
	`952`	`+ else if (path->jpath.jointype == JOIN_RIGHT)`
	`953`	`+ innerscansel = 1.0;`
`949`	`954`	`}`
`950`	`955`	`else`
`951`	`956`	`{`
`952`		`- /* cope with clauseless mergejoin */`
	`957`	`+ /* cope with clauseless or full mergejoin */`
`953`	`958`	`outerscansel = innerscansel = 1.0;`
`954`	`959`	`}`
`955`	`960`