1 files changed, 41 insertions, 19 deletions

diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index c05bb1e0818..1dcb0f57f44 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -567,16 +567,21 @@ StartReplication(StartReplicationCmd *cmd)
 	 */
 	if (sendTimeLineIsHistoric)
 	{
-		char		str[11];
-		snprintf(str, sizeof(str), "%u", sendTimeLineNextTLI);
+		char		tli_str[11];
+		char		startpos_str[8+1+8+1];
 
-		pq_beginmessage(&buf, 'T'); /* RowDescription */
-		pq_sendint(&buf, 1, 2);		/* 1 field */
+		snprintf(tli_str, sizeof(tli_str), "%u", sendTimeLineNextTLI);
+		snprintf(startpos_str, sizeof(startpos_str), "%X/%X",
+				 (uint32) (sendTimeLineValidUpto >> 32),
+				 (uint32) sendTimeLineValidUpto);
+
+		pq_beginmessage(&buf, 'T'); 	/* RowDescription */
+		pq_sendint(&buf, 2, 2);			/* 2 fields */
 
 		/* Field header */
 		pq_sendstring(&buf, "next_tli");
-		pq_sendint(&buf, 0, 4);		/* table oid */
-		pq_sendint(&buf, 0, 2);		/* attnum */
+		pq_sendint(&buf, 0, 4);			/* table oid */
+		pq_sendint(&buf, 0, 2);			/* attnum */
 		/*
 		 * int8 may seem like a surprising data type for this, but in theory
 		 * int4 would not be wide enough for this, as TimeLineID is unsigned.
@@ -585,13 +590,26 @@ StartReplication(StartReplicationCmd *cmd)
 		pq_sendint(&buf, -1, 2);
 		pq_sendint(&buf, 0, 4);
 		pq_sendint(&buf, 0, 2);
+
+		pq_sendstring(&buf, "next_tli_startpos");
+		pq_sendint(&buf, 0, 4);			/* table oid */
+		pq_sendint(&buf, 0, 2);			/* attnum */
+		pq_sendint(&buf, TEXTOID, 4);	/* type oid */
+		pq_sendint(&buf, -1, 2);
+		pq_sendint(&buf, 0, 4);
+		pq_sendint(&buf, 0, 2);
 		pq_endmessage(&buf);
 
 		/* Data row */
 		pq_beginmessage(&buf, 'D');
-		pq_sendint(&buf, 1, 2);		/* number of columns */
-		pq_sendint(&buf, strlen(str), 4);	/* length */
-		pq_sendbytes(&buf, str, strlen(str));
+		pq_sendint(&buf, 2, 2);			/* number of columns */
+
+		pq_sendint(&buf, strlen(tli_str), 4);	/* length */
+		pq_sendbytes(&buf, tli_str, strlen(tli_str));
+
+		pq_sendint(&buf, strlen(startpos_str), 4);	/* length */
+		pq_sendbytes(&buf, startpos_str, strlen(startpos_str));
+
 		pq_endmessage(&buf);
 	}
 
@@ -1462,19 +1480,10 @@ XLogSend(bool *caughtup)
 
 			history = readTimeLineHistory(ThisTimeLineID);
 			sendTimeLineValidUpto = tliSwitchPoint(sendTimeLine, history, &sendTimeLineNextTLI);
-			Assert(sentPtr <= sendTimeLineValidUpto);
+
 			Assert(sendTimeLine < sendTimeLineNextTLI);
 			list_free_deep(history);
 
-			/* the current send pointer should be <= the switchpoint */
-			if (!(sentPtr <= sendTimeLineValidUpto))
-				elog(ERROR, "server switched off timeline %u at %X/%X, but walsender already streamed up to %X/%X",
-					 sendTimeLine,
-					 (uint32) (sendTimeLineValidUpto >> 32),
-					 (uint32) sendTimeLineValidUpto,
-					 (uint32) (sentPtr >> 32),
-					 (uint32) sentPtr);
-
 			sendTimeLineIsHistoric = true;
 
 			SendRqstPtr = sendTimeLineValidUpto;
@@ -1498,6 +1507,15 @@ XLogSend(bool *caughtup)
 	/*
 	 * If this is a historic timeline and we've reached the point where we
 	 * forked to the next timeline, stop streaming.
+	 *
+	 * Note: We might already have sent WAL > sendTimeLineValidUpto. The
+	 * startup process will normally replay all WAL that has been received from
+	 * the master, before promoting, but if the WAL streaming is terminated at
+	 * a WAL page boundary, the valid portion of the timeline might end in the
+	 * middle of a WAL record. We might've already sent the first half of that
+	 * partial WAL record to the cascading standby, so that sentPtr >
+	 * sendTimeLineValidUpto. That's OK; the cascading standby can't replay the
+	 * partial WAL record either, so it can still follow our timeline switch.
 	 */
 	if (sendTimeLineIsHistoric && sendTimeLineValidUpto <= sentPtr)
 	{
@@ -1511,6 +1529,10 @@ XLogSend(bool *caughtup)
 		streamingDoneSending = true;
 
 		*caughtup = true;
+
+		elog(DEBUG1, "walsender reached end of timeline at %X/%X (sent up to %X/%X)",
+			 (uint32) (sendTimeLineValidUpto >> 32), (uint32) sendTimeLineValidUpto,
+			 (uint32) (sentPtr >> 32), (uint32) sentPtr);
 		return;
 	}