Ensure all replication message info is available and correct via WalRcv

src/backend/replication/walreceiver.c

@@ -218,7 +218,7 @@ WalReceiverMain(void)
 	startpoint = walrcv->receiveStart;
 
 	/* Initialise to a sanish value */
-	walrcv->lastMsgSendTime = walrcv->lastMsgReceiptTime = GetCurrentTimestamp();
+	walrcv->lastMsgSendTime = walrcv->lastMsgReceiptTime = walrcv->latestWalEndTime = GetCurrentTimestamp();
 
 	SpinLockRelease(&walrcv->mutex);
 
@@ -749,6 +749,9 @@ ProcessWalSndrMessage(XLogRecPtr walEnd, TimestampTz sendTime)
 
 	/* Update shared-memory status */
 	SpinLockAcquire(&walrcv->mutex);
+	if (XLByteLT(walrcv->latestWalEnd, walEnd))
+		walrcv->latestWalEndTime = sendTime;
+	walrcv->latestWalEnd = walEnd;
 	walrcv->lastMsgSendTime = sendTime;
 	walrcv->lastMsgReceiptTime = lastMsgReceiptTime;
 	SpinLockRelease(&walrcv->mutex);

src/backend/replication/walreceiverfuncs.c

@@ -260,7 +260,7 @@ GetReplicationApplyDelay(void)
 
 	replayPtr = GetXLogReplayRecPtr(NULL);
 
-	if (XLByteLE(receivePtr, replayPtr))
+	if (XLByteEQ(receivePtr, replayPtr))
 		return 0;
 
 	TimestampDifference(GetCurrentChunkReplayStartTime(),

src/include/replication/walreceiver.h

@@ -83,6 +83,12 @@ typedef struct
 	TimestampTz lastMsgSendTime;
 	TimestampTz lastMsgReceiptTime;
 
+	/*
+	 * Latest reported end of WAL on the sender
+	 */
+	XLogRecPtr	latestWalEnd;
+	TimestampTz latestWalEndTime;
+
 	/*
 	 * connection string; is used for walreceiver to connect with the primary.
 	 */