Call pg_switch_wal() for PAGE backup after pg_start_backup()

Author: Arthur Zakirov

src/backup.c

@@ -80,6 +80,7 @@ static void backup_files(void *arg);
 static void do_backup_database(parray *backup_list);
 
 static void pg_start_backup(const char *label, bool smooth, pgBackup *backup);
+static void pg_switch_wal(PGconn *conn);
 static void pg_stop_backup(pgBackup *backup);
 static int checkpoint_timeout(void);
 
@@ -639,19 +640,53 @@ pg_start_backup(const char *label, bool smooth, pgBackup *backup)
 
 	PQclear(res);
 
+	if (current.backup_mode == BACKUP_MODE_DIFF_PAGE)
+		/*
+		 * Switch to a new WAL segment. It is necessary to get archived WAL
+		 * segment, which includes start LSN of current backup.
+		 */
+		pg_switch_wal(conn);
+
 	if (!stream_wal)
+	{
 		/*
 		 * Do not wait start_lsn for stream backup.
 		 * Because WAL streaming will start after pg_start_backup() in stream
 		 * mode.
 		 */
-		wait_wal_lsn(backup->start_lsn, true);
+		/* In PAGE mode wait for current segment... */
+		if (current.backup_mode == BACKUP_MODE_DIFF_PAGE)
+			wait_wal_lsn(backup->start_lsn, false);
+		/* ...for others wait for previous segment */
+		else
+			wait_wal_lsn(backup->start_lsn, true);
+	}
 
 	/* Wait for start_lsn to be replayed by replica */
 	if (from_replica)
 		wait_replica_wal_lsn(backup->start_lsn, true);
 }
 
+/*
+ * Switch to a new WAL segment. It should be called only for master.
+ */
+static void
+pg_switch_wal(PGconn *conn)
+{
+	PGresult   *res;
+
+	/* Remove annoying NOTICE messages generated by backend */
+	res = pgut_execute(conn, "SET client_min_messages = warning;", 0, NULL);
+	PQclear(res);
+
+	if (server_version >= 100000)
+		res = pgut_execute(conn, "SELECT * FROM pg_switch_wal()", 0, NULL);
+	else
+		res = pgut_execute(conn, "SELECT * FROM pg_switch_xlog()", 0, NULL);
+
+	PQclear(res);
+}
+
 /*
  * Check if the instance supports ptrack
  * TODO Maybe we should rather check ptrack_version()?
@@ -974,7 +1009,7 @@ pg_stop_backup(pgBackup *backup)
 	uint32		xrecoff;
 	XLogRecPtr	restore_lsn = InvalidXLogRecPtr;
 	bool sent = false;
-	int pg_stop_backup_timeout = 0;
+	int			pg_stop_backup_timeout = 0;
 
 	/*
 	 * We will use this values if there are no transactions between start_lsn
@@ -1050,8 +1085,6 @@ pg_stop_backup(pgBackup *backup)
 	 * Wait for the result of pg_stop_backup(),
 	 * but no longer than PG_STOP_BACKUP_TIMEOUT seconds
 	 */
-	elog(INFO, "wait for pg_stop_backup()");
-
 	while (1)
 	{
 		if (!PQconsumeInput(conn) || PQisBusy(conn))
@@ -1064,6 +1097,10 @@ pg_stop_backup(pgBackup *backup)
 				pgut_cancel(conn);
 				elog(ERROR, "interrupted during waiting for pg_stop_backup");
 			}
+
+			if (pg_stop_backup_timeout == 1)
+				elog(INFO, "wait for pg_stop_backup()");
+
 			/*
 			 * If postgres haven't answered in PG_STOP_BACKUP_TIMEOUT seconds,
 			 * send an interrupt.