From 757f40345141bf31ea380128cbf2fd2dde4a2798 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Mon, 1 Feb 1999 04:20:50 +0000
Subject: [PATCH] Tighten coding in samekeys().  Pretty braindead change, but
 it saves almost 10% of the runtime in Charles Hornberger's optimizer example,
 so what the heck ...

---
 src/backend/optimizer/util/keys.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/src/backend/optimizer/util/keys.c b/src/backend/optimizer/util/keys.c
index 3e2372339d..685e01cbaf 100644
--- a/src/backend/optimizer/util/keys.c
+++ b/src/backend/optimizer/util/keys.c
@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/util/Attic/keys.c,v 1.9 1998/09/01 04:30:07 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/util/Attic/keys.c,v 1.10 1999/02/01 04:20:50 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -120,16 +120,20 @@ extract_subkey(JoinKey *jk, int which_subkey)
 bool
 samekeys(List *keys1, List *keys2)
 {
-	bool		allmember = true;
 	List	   *key1,
 			   *key2;
 
 	for (key1 = keys1, key2 = keys2; key1 != NIL && key2 != NIL;
 		 key1 = lnext(key1), key2 = lnext(key2))
 		if (!member(lfirst(key1), lfirst(key2)))
-			allmember = false;
+			return false;
 
-	if ((length(keys2) >= length(keys1)) && allmember)
+	/* Now the result should be true if list keys2 has at least as many
+	 * entries as keys1, ie, we did not fall off the end of keys2 first.
+	 * If key1 is now NIL then we hit the end of keys1 before or at the
+	 * same time as the end of keys2.
+	 */
+	if (key1 == NIL)
 		return true;
 	else
 		return false;