Make pg_receivexlog and pg_basebackup -X stream work across timeline switches.

This mirrors the changes done earlier to the server in standby mode. When
receivelog reaches the end of a timeline, as reported by the server, it
fetches the timeline history file of the next timeline, and restarts
streaming from the new timeline by issuing a new START_STREAMING command.

When pg_receivexlog crosses a timeline, it leaves the .partial suffix on the
last segment on the old timeline. This helps you to tell apart a partial
segment left in the directory because of a timeline switch, and a completed
segment. If you just follow a single server, it won't make a difference, but
it can be significant in more complicated scenarios where new WAL is still
generated on the old timeline.

This includes two small changes to the streaming replication protocol:
First, when you reach the end of timeline while streaming, the server now
sends the TLI of the next timeline in the server's history to the client.
pg_receivexlog uses that as the next timeline, so that it doesn't need to
parse the timeline history file like a standby server does. Second, when
BASE_BACKUP command sends the begin and end WAL positions, it now also sends
the timeline IDs corresponding the positions.

1 files changed, 14 insertions, 9 deletions

diff --git a/src/bin/pg_basebackup/pg_basebackup.c b/src/bin/pg_basebackup/pg_basebackup.c
index a684c0c6fcf..b6f774469b1 100644
--- a/src/bin/pg_basebackup/pg_basebackup.c
+++ b/src/bin/pg_basebackup/pg_basebackup.c
@@ -243,7 +243,7 @@ LogStreamerMain(logstreamer_param *param)
 	if (!ReceiveXlogStream(param->bgconn, param->startptr, param->timeline,
 						   param->sysidentifier, param->xlogdir,
 						   reached_end_position, standby_message_timeout,
-						   true))
+						   NULL))
 
 		/*
 		 * Any errors will already have been reported in the function process,
@@ -1220,7 +1220,7 @@ BaseBackup(void)
 {
 	PGresult   *res;
 	char	   *sysidentifier;
-	uint32		timeline;
+	uint32		starttli;
 	char		current_path[MAXPGPATH];
 	char		escaped_label[MAXPGPATH];
 	int			i;
@@ -1259,7 +1259,6 @@ BaseBackup(void)
 		disconnect_and_exit(1);
 	}
 	sysidentifier = pg_strdup(PQgetvalue(res, 0, 0));
-	timeline = atoi(PQgetvalue(res, 0, 1));
 	PQclear(res);
 
 	/*
@@ -1291,18 +1290,24 @@ BaseBackup(void)
 				progname, PQerrorMessage(conn));
 		disconnect_and_exit(1);
 	}
-	if (PQntuples(res) != 1)
+	if (PQntuples(res) != 1 || PQnfields(res) < 2)
 	{
-		fprintf(stderr, _("%s: no start point returned from server\n"),
-				progname);
+		fprintf(stderr,
+				_("%s: server returned unexpected response to BASE_BACKUP command; got %d rows and %d fields, expected %d rows and %d fields\n"),
+				progname, PQntuples(res), PQnfields(res), 1, 2);
 		disconnect_and_exit(1);
 	}
+
 	strcpy(xlogstart, PQgetvalue(res, 0, 0));
-	if (verbose && includewal)
-		fprintf(stderr, "transaction log start point: %s\n", xlogstart);
+	starttli = atoi(PQgetvalue(res, 0, 1));
+
 	PQclear(res);
 	MemSet(xlogend, 0, sizeof(xlogend));
 
+	if (verbose && includewal)
+		fprintf(stderr, _("transaction log start point: %s on timeline %u\n"),
+				xlogstart, starttli);
+
 	/*
 	 * Get the header
 	 */
@@ -1358,7 +1363,7 @@ BaseBackup(void)
 		if (verbose)
 			fprintf(stderr, _("%s: starting background WAL receiver\n"),
 					progname);
-		StartLogStreamer(xlogstart, timeline, sysidentifier);
+		StartLogStreamer(xlogstart, starttli, sysidentifier);
 	}
 
 	/*