Update the location of last removed WAL segment in shared memory only

after actually removing one, so that if we can't remove segments because
WAL archiving is lagging behind, we don't unnecessarily forbid streaming
the old not-yet-archived segments that are still perfectly valid. Per
suggestion from Fujii Masao.

src/backend/access/transam/xlog.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.392 2010/04/12 09:52:29 heikki Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.393 2010/04/12 10:40:42 heikki Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -546,6 +546,7 @@ static void ExecuteRecoveryCommand(char *command, char *commandName,
 					   bool failOnerror);
 static void PreallocXlogFiles(XLogRecPtr endptr);
 static void RemoveOldXlogFiles(uint32 log, uint32 seg, XLogRecPtr endptr);
+static void UpdateLastRemovedPtr(char *filename);
 static void ValidateXLOGDirectoryStructure(void);
 static void CleanupBackupHistory(void);
 static void UpdateMinRecoveryPoint(XLogRecPtr lsn, bool force);
@@ -3168,6 +3169,31 @@ XLogGetLastRemoved(uint32 *log, uint32 *seg)
 	SpinLockRelease(&xlogctl->info_lck);
 }
 
+/*
+ * Update the last removed log/seg pointer in shared memory, to reflect
+ * that the given XLOG file has been removed.
+ */
+static void
+UpdateLastRemovedPtr(char *filename)
+{
+	/* use volatile pointer to prevent code rearrangement */
+	volatile XLogCtlData *xlogctl = XLogCtl;
+	uint32		tli,
+				log,
+				seg;
+
+	XLogFromFileName(filename, &tli, &log, &seg);
+
+	SpinLockAcquire(&xlogctl->info_lck);
+	if (log > xlogctl->lastRemovedLog ||
+		(log == xlogctl->lastRemovedLog && seg > xlogctl->lastRemovedSeg))
+	{
+		xlogctl->lastRemovedLog = log;
+		xlogctl->lastRemovedSeg = seg;
+	}
+	SpinLockRelease(&xlogctl->info_lck);
+}
+
 /*
  * Recycle or remove all log files older or equal to passed log/seg#
  *
@@ -3189,20 +3215,8 @@ RemoveOldXlogFiles(uint32 log, uint32 seg, XLogRecPtr endptr)
 	char		newpath[MAXPGPATH];
 #endif
 	struct stat statbuf;
-	/* use volatile pointer to prevent code rearrangement */
-	volatile XLogCtlData *xlogctl = XLogCtl;
 
-	/* Update the last removed location in shared memory first */
-	SpinLockAcquire(&xlogctl->info_lck);
-	if (log > xlogctl->lastRemovedLog ||
-		(log == xlogctl->lastRemovedLog && seg > xlogctl->lastRemovedSeg))
-	{
-		xlogctl->lastRemovedLog = log;
-		xlogctl->lastRemovedSeg = seg;
-	}
-	SpinLockRelease(&xlogctl->info_lck);
-
-	elog(DEBUG1, "removing WAL segments older than %X/%X", log, seg);
+	elog(DEBUG2, "removing WAL segments older than %X/%X", log, seg);
 
 	/*
 	 * Initialize info about where to try to recycle to.  We allow recycling
@@ -3252,6 +3266,9 @@ RemoveOldXlogFiles(uint32 log, uint32 seg, XLogRecPtr endptr)
 			{
 				snprintf(path, MAXPGPATH, XLOGDIR "/%s", xlde->d_name);
 
+				/* Update the last removed location in shared memory first */
+				UpdateLastRemovedPtr(xlde->d_name);
+
 				/*
 				 * Before deleting the file, see if it can be recycled as a
 				 * future log segment. Only recycle normal files, pg_standby

src/include/access/xlog_internal.h

@@ -11,7 +11,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/access/xlog_internal.h,v 1.31 2010/03/28 09:27:02 sriggs Exp $
+ * $PostgreSQL: pgsql/src/include/access/xlog_internal.h,v 1.32 2010/04/12 10:40:43 heikki Exp $
  */
 #ifndef XLOG_INTERNAL_H
 #define XLOG_INTERNAL_H
@@ -216,6 +216,9 @@ typedef XLogLongPageHeaderData *XLogLongPageHeader;
 #define XLogFileName(fname, tli, log, seg)	\
 	snprintf(fname, MAXFNAMELEN, "%08X%08X%08X", tli, log, seg)
 
+#define XLogFromFileName(fname, tli, log, seg)	\
+	sscanf(fname, "%08X%08X%08X", tli, log, seg)
+
 #define XLogFilePath(path, tli, log, seg)	\
 	snprintf(path, MAXPGPATH, XLOGDIR "/%08X%08X%08X", tli, log, seg)