diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 29a25eb9035e1234d8473a7ed0b86804e39fb375..74357ace295d1aaf4dac2360cc6a69b3a783a1ce 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -169,7 +169,7 @@ static void WalSndLoop(void);
static void InitWalSenderSlot(void);
static void WalSndKill(int code, Datum arg);
static void XLogSend(bool *caughtup);
-static XLogRecPtr GetStandbyFlushRecPtr(TimeLineID currentTLI);
+static XLogRecPtr GetStandbyFlushRecPtr(void);
static void IdentifySystem(void);
static void StartReplication(StartReplicationCmd *cmd);
static void ProcessStandbyMessage(void);
@@ -250,7 +250,7 @@ IdentifySystem(void)
if (am_cascading_walsender)
{
/* this also updates ThisTimeLineID */
- logptr = GetStandbyFlushRecPtr(0);
+ logptr = GetStandbyFlushRecPtr();
}
else
logptr = GetInsertRecPtr();
@@ -423,7 +423,7 @@ StartReplication(StartReplicationCmd *cmd)
if (am_cascading_walsender)
{
/* this also updates ThisTimeLineID */
- FlushPtr = GetStandbyFlushRecPtr(0);
+ FlushPtr = GetStandbyFlushRecPtr();
}
else
FlushPtr = GetFlushRecPtr();
@@ -1310,7 +1310,6 @@ static void
XLogSend(bool *caughtup)
{
XLogRecPtr SendRqstPtr;
- XLogRecPtr FlushPtr;
XLogRecPtr startptr;
XLogRecPtr endptr;
Size nbytes;
@@ -1321,33 +1320,39 @@ XLogSend(bool *caughtup)
return;
}
- /*
- * Attempt to send all data that's already been written out and fsync'd to
- * disk. We cannot go further than what's been written out given the
- * current implementation of XLogRead(). And in any case it's unsafe to
- * send WAL that is not securely down to disk on the master: if the master
- * subsequently crashes and restarts, slaves must not have applied any WAL
- * that gets lost on the master.
- */
- if (am_cascading_walsender)
- FlushPtr = GetStandbyFlushRecPtr(sendTimeLine);
- else
- FlushPtr = GetFlushRecPtr();
-
- /*
- * In a cascading standby, the current recovery target timeline can
- * change, or we can be promoted. In either case, the current timeline
- * becomes historic. We need to detect that so that we don't try to stream
- * past the point where we switched to another timeline. It's checked
- * after calculating FlushPtr, to avoid a race condition: if the timeline
- * becomes historic just after we checked that it was still current, it
- * should still be OK to stream it up to the FlushPtr that was calculated
- * before it became historic.
- */
- if (!sendTimeLineIsHistoric && am_cascading_walsender)
+ /* Figure out how far we can safely send the WAL. */
+ if (sendTimeLineIsHistoric)
{
+ /*
+ * Streaming an old timeline timeline that's in this server's history,
+ * but is not the one we're currently inserting or replaying. It can
+ * be streamed up to the point where we switched off that timeline.
+ */
+ SendRqstPtr = sendTimeLineValidUpto;
+ }
+ else if (am_cascading_walsender)
+ {
+ /*
+ * Streaming the latest timeline on a standby.
+ *
+ * Attempt to send all WAL that has already been replayed, so that
+ * we know it's valid. If we're receiving WAL through streaming
+ * replication, it's also OK to send any WAL that has been received
+ * but not replayed.
+ *
+ * The timeline we're recovering from can change, or we can be
+ * promoted. In either case, the current timeline becomes historic.
+ * We need to detect that so that we don't try to stream past the
+ * point where we switched to another timeline. We check for promotion
+ * or timeline switch after calculating FlushPtr, to avoid a race
+ * condition: if the timeline becomes historic just after we checked
+ * that it was still current, it's still be OK to stream it up to the
+ * FlushPtr that was calculated before it became historic.
+ */
bool becameHistoric = false;
+ SendRqstPtr = GetStandbyFlushRecPtr();
+
if (!RecoveryInProgress())
{
/*
@@ -1361,7 +1366,8 @@ XLogSend(bool *caughtup)
{
/*
* Still a cascading standby. But is the timeline we're sending
- * still the one recovery is recovering from?
+ * still the one recovery is recovering from? ThisTimeLineID was
+ * updated by the GetStandbyFlushRecPtr() call above.
*/
if (sendTimeLine != ThisTimeLineID)
becameHistoric = true;
@@ -1391,8 +1397,24 @@ XLogSend(bool *caughtup)
(uint32) sentPtr);
sendTimeLineIsHistoric = true;
+
+ SendRqstPtr = sendTimeLineValidUpto;
}
}
+ else
+ {
+ /*
+ * Streaming the current timeline on a master.
+ *
+ * Attempt to send all data that's already been written out and
+ * fsync'd to disk. We cannot go further than what's been written out
+ * given the current implementation of XLogRead(). And in any case
+ * it's unsafe to send WAL that is not securely down to disk on the
+ * master: if the master subsequently crashes and restarts, slaves
+ * must not have applied any WAL that gets lost on the master.
+ */
+ SendRqstPtr = GetFlushRecPtr();
+ }
/*
* If this is a historic timeline and we've reached the point where we
@@ -1413,15 +1435,7 @@ XLogSend(bool *caughtup)
return;
}
- /*
- * Stream up to the point known to be flushed to disk, or to the end of
- * this timeline, whichever comes first.
- */
- if (sendTimeLineIsHistoric && XLByteLT(sendTimeLineValidUpto, FlushPtr))
- SendRqstPtr = sendTimeLineValidUpto;
- else
- SendRqstPtr = FlushPtr;
-
+ /* Do we have any work to do? */
Assert(XLByteLE(sentPtr, SendRqstPtr));
if (XLByteLE(SendRqstPtr, sentPtr))
{
@@ -1522,15 +1536,11 @@ XLogSend(bool *caughtup)
* can be sent to the standby. This should only be called when in recovery,
* ie. we're streaming to a cascaded standby.
*
- * If currentTLI is non-zero, the function returns the point that the WAL on
- * the given timeline has been flushed upto. If recovery has already switched
- * to a different timeline, InvalidXLogRecPtr is returned.
- *
* As a side-effect, ThisTimeLineID is updated to the TLI of the last
* replayed WAL record.
*/
static XLogRecPtr
-GetStandbyFlushRecPtr(TimeLineID currentTLI)
+GetStandbyFlushRecPtr(void)
{
XLogRecPtr replayPtr;
TimeLineID replayTLI;
@@ -1549,11 +1559,8 @@ GetStandbyFlushRecPtr(TimeLineID currentTLI)
ThisTimeLineID = replayTLI;
- if (currentTLI != replayTLI && currentTLI != 0)
- return InvalidXLogRecPtr;
-
result = replayPtr;
- if (receiveTLI == currentTLI && receivePtr > replayPtr)
+ if (receiveTLI == ThisTimeLineID && receivePtr > replayPtr)
result = receivePtr;
return result;