Even though I'd like to see full_page_writes go away before 8.1,

a minimum requirement is that it not completely break the system
meanwhile.  Put the test in the right place.

src/backend/access/transam/xlog.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.207 2005/07/05 23:18:09 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.208 2005/07/08 04:07:26 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -595,9 +595,7 @@ begin:;
 				{
 					/* OK, put it in this slot */
 					dtbuf[i] = rdt->buffer;
-					/* If fsync is off, no need to backup pages. */
-					if (fullPageWrites &&
-						XLogCheckBuffer(rdt, &(dtbuf_lsn[i]), &(dtbuf_xlg[i])))
+					if (XLogCheckBuffer(rdt, &(dtbuf_lsn[i]), &(dtbuf_xlg[i])))
 					{
 						dtbuf_bkp[i] = true;
 						rdt->data = NULL;
@@ -947,7 +945,8 @@ XLogCheckBuffer(XLogRecData *rdata,
 	 */
 	*lsn = page->pd_lsn;
 
-	if (XLByteLE(page->pd_lsn, RedoRecPtr))
+	if (fullPageWrites &&
+		XLByteLE(page->pd_lsn, RedoRecPtr))
 	{
 		/*
 		 * The page needs to be backed up, so set up *bkpb