Fix corner-case bug in tracking of latest removed WAL segment during

hlinnaka · hlinnaka · commit 268fecc62cde · 2010-11-01T10:04:45.000+02:00
streaming replication. We used log/seg 0/0 to indicate that no WAL segments
have been removed since startup, but 0/0 is a valid value for the very first
WAL segment after initdb. To make that disambiguous, store
(latest removed WAL segment + 1) in the global variable.

Per report from Matt Chesler, also reproduced by Greg Smith.
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
@@ -363,7 +363,7 @@ typedef struct XLogCtlData
 	uint32		ckptXidEpoch;	/* nextXID & epoch of latest checkpoint */
 	TransactionId ckptXid;
 	XLogRecPtr	asyncXactLSN; /* LSN of newest async commit/abort */
-	uint32		lastRemovedLog; /* latest removed/recycled XLOG segment */
+	uint32		lastRemovedLog; /* latest removed/recycled XLOG segment + 1 */
 	uint32		lastRemovedSeg;
 
 	/* Protected by WALWriteLock: */
@@ -3210,8 +3210,10 @@ PreallocXlogFiles(XLogRecPtr endptr)
 }
 
 /*
- * Get the log/seg of the latest removed or recycled WAL segment.
- * Returns 0 if no WAL segments have been removed since startup.
+ * Get the log/seg of the first WAL segment that has not been removed or
+ * recycled. In other words, the log/seg of the last removed/recycled WAL
+ * segment + 1.
+ * Returns 0/0 if no WAL segments have been removed since startup.
  */
 void
 XLogGetLastRemoved(uint32 *log, uint32 *seg)
@@ -3239,6 +3241,7 @@ UpdateLastRemovedPtr(char *filename)
 				seg;
 
 	XLogFromFileName(filename, &tli, &log, &seg);
+	NextLogSeg(log, seg);
 
 	SpinLockAcquire(&xlogctl->info_lck);
 	if (log > xlogctl->lastRemovedLog ||
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
@@ -630,7 +630,7 @@ XLogRead(char *buf, XLogRecPtr recptr, Size nbytes)
 	XLogGetLastRemoved(&lastRemovedLog, &lastRemovedSeg);
 	XLByteToSeg(startRecPtr, log, seg);
 	if (log < lastRemovedLog ||
-		(log == lastRemovedLog && seg <= lastRemovedSeg))
+		(log == lastRemovedLog && seg < lastRemovedSeg))
 	{
 		char		filename[MAXFNAMELEN];
 

Original file line number	Diff line number	Diff line change
`@@ -630,7 +630,7 @@ XLogRead(char *buf, XLogRecPtr recptr, Size nbytes)`
`630`	`630`	`XLogGetLastRemoved(&lastRemovedLog, &lastRemovedSeg);`
`631`	`631`	`XLByteToSeg(startRecPtr, log, seg);`
`632`	`632`	`if (log < lastRemovedLog \|\|`
`633`		`- (log == lastRemovedLog && seg <= lastRemovedSeg))`
	`633`	`+ (log == lastRemovedLog && seg < lastRemovedSeg))`
`634`	`634`	`{`
`635`	`635`	`char filename[MAXFNAMELEN];`
`636`	`636`