Only recycle normal files in pg_xlog as WAL segments. pg_standby creates

symbolic links with the -l option, and as Fujii Masao pointed out we ended up
overwriting files in the archive directory before this patch. Patch by
Aidan Van Dyk, Fujii Masao and me.

Backpatch to 8.3, where pg_standby was introduced.

src/backend/access/transam/xlog.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.341 2009/05/28 11:02:16 heikki Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.342 2009/06/02 06:18:06 heikki Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -3006,6 +3006,7 @@ RemoveOldXlogFiles(uint32 log, uint32 seg, XLogRecPtr endptr)
 	struct dirent *xlde;
 	char		lastoff[MAXFNAMELEN];
 	char		path[MAXPGPATH];
+	struct stat statbuf;
 
 	/*
 	 * Initialize info about where to try to recycle to.  We allow recycling
@@ -3046,11 +3047,13 @@ RemoveOldXlogFiles(uint32 log, uint32 seg, XLogRecPtr endptr)
 
 				/*
 				 * Before deleting the file, see if it can be recycled as a
-				 * future log segment.
+				 * future log segment. Only recycle normal files, pg_standby
+				 * for example can create symbolic links pointing to a
+				 * separate archive directory.
 				 */
-				if (InstallXLogFileSegment(&endlogId, &endlogSeg, path,
-										   true, &max_advance,
-										   true))
+				if (lstat(path, &statbuf) == 0 && S_ISREG(statbuf.st_mode) &&
+					InstallXLogFileSegment(&endlogId, &endlogSeg, path,
+										   true, &max_advance, true))
 				{
 					ereport(DEBUG2,
 							(errmsg("recycled transaction log file \"%s\"",