From 082aca9ec2854f8e25730c37411685f51a6277de Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sun, 10 Feb 2008 20:39:08 +0000
Subject: [PATCH] Fix PageGetExactFreeSpace() so that it actually behaves
 sensibly if pd_lower > pd_upper, rather than merely claiming to.  This would
 only matter if the page header were corrupt, which shouldn't occur, but ...

---
 src/backend/storage/page/bufpage.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/backend/storage/page/bufpage.c b/src/backend/storage/page/bufpage.c
index 32b80c182f..ad1c8c3ed3 100644
--- a/src/backend/storage/page/bufpage.c
+++ b/src/backend/storage/page/bufpage.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/page/bufpage.c,v 1.77 2008/01/01 19:45:52 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/page/bufpage.c,v 1.78 2008/02/10 20:39:08 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -489,6 +489,9 @@ PageGetExactFreeSpace(Page page)
 	space = (int) ((PageHeader) page)->pd_upper -
 		(int) ((PageHeader) page)->pd_lower;
 
+	if (space < 0)
+		return 0;
+
 	return (Size) space;
 }