PGPRO-2180: Rewrite stop_lsn during pg_stop_backup

Author: za-arthur

src/backup.c

@@ -109,7 +109,7 @@ static int checkpoint_timeout(void);
 //static void backup_list_file(parray *files, const char *root, )
 static void parse_backup_filelist_filenames(parray *files, const char *root);
 static XLogRecPtr wait_wal_lsn(XLogRecPtr lsn, bool is_start_lsn,
-							   bool wait_prev_lsn, bool wait_prev_segment);
+							   bool wait_prev_segment);
 static void wait_replica_wal_lsn(XLogRecPtr lsn, bool is_start_backup);
 static void make_pagemap_from_ptrack(parray *files);
 static void *StreamLog(void *arg);
@@ -1166,15 +1166,15 @@ pg_start_backup(const char *label, bool smooth, pgBackup *backup)
 
 	if (current.backup_mode == BACKUP_MODE_DIFF_PAGE)
 		/* In PAGE mode wait for current segment... */
-		wait_wal_lsn(backup->start_lsn, true, false, false);
+		wait_wal_lsn(backup->start_lsn, true, false);
 	/*
 	 * Do not wait start_lsn for stream backup.
 	 * Because WAL streaming will start after pg_start_backup() in stream
 	 * mode.
 	 */
 	else if (!stream_wal)
 		/* ...for others wait for previous segment */
-		wait_wal_lsn(backup->start_lsn, true, false, true);
+		wait_wal_lsn(backup->start_lsn, true, true);
 
 	/* In case of backup from replica for PostgreSQL 9.5
 	 * wait for start_lsn to be replayed by replica
@@ -1507,8 +1507,7 @@ pg_ptrack_get_and_clear(Oid tablespace_oid, Oid db_oid, Oid rel_filenode,
  * returns InvalidXLogRecPtr.
  */
 static XLogRecPtr
-wait_wal_lsn(XLogRecPtr lsn, bool is_start_lsn, bool wait_prev_lsn,
-			 bool wait_prev_segment)
+wait_wal_lsn(XLogRecPtr lsn, bool is_start_lsn, bool wait_prev_segment)
 {
 	TimeLineID	tli;
 	XLogSegNo	targetSegNo;
@@ -1519,7 +1518,6 @@ wait_wal_lsn(XLogRecPtr lsn, bool is_start_lsn, bool wait_prev_lsn,
 	bool		file_exists = false;
 	uint32		try_count = 0,
 				timeout;
-	char	   *prior_to = (wait_prev_lsn) ? " prior to " : "";
 
 #ifdef HAVE_LIBZ
 	char		gz_wal_segment_path[MAXPGPATH];
@@ -1565,8 +1563,8 @@ wait_wal_lsn(XLogRecPtr lsn, bool is_start_lsn, bool wait_prev_lsn,
 	if (wait_prev_segment)
 		elog(LOG, "Looking for segment: %s", wal_segment);
 	else
-		elog(LOG, "Looking for LSN %s%X/%X in segment: %s",
-			 prior_to, (uint32) (lsn >> 32), (uint32) lsn, wal_segment);
+		elog(LOG, "Looking for LSN %X/%X in segment: %s",
+			 (uint32) (lsn >> 32), (uint32) lsn, wal_segment);
 
 #ifdef HAVE_LIBZ
 	snprintf(gz_wal_segment_path, sizeof(gz_wal_segment_path), "%s.gz",
@@ -1602,16 +1600,19 @@ wait_wal_lsn(XLogRecPtr lsn, bool is_start_lsn, bool wait_prev_lsn,
 			/*
 			 * A WAL segment found. Check LSN on it.
 			 */
-			if (!wait_prev_lsn)
+			if (wal_contains_lsn(wal_segment_dir, lsn, tli, xlog_seg_size))
+				/* Target LSN was found */
 			{
-				if (wal_contains_lsn(wal_segment_dir, lsn, tli, xlog_seg_size))
-					/* Target LSN was found */
-				{
-					elog(LOG, "Found LSN: %X/%X", (uint32) (lsn >> 32), (uint32) lsn);
-					return lsn;
-				}
+				elog(LOG, "Found LSN: %X/%X", (uint32) (lsn >> 32), (uint32) lsn);
+				return lsn;
 			}
-			else
+
+			/*
+			 * If we failed to get LSN of valid record in a reasonable time, try
+			 * to get LSN of last valid record prior to the target LSN. But only
+			 * in case of a backup from a replica.
+			 */
+			if (!exclusive_backup && current.from_replica)
 			{
 				XLogRecPtr	res;
 
@@ -1620,7 +1621,8 @@ wait_wal_lsn(XLogRecPtr lsn, bool is_start_lsn, bool wait_prev_lsn,
 				if (!XLogRecPtrIsInvalid(res))
 				{
 					/* LSN of the prior record was found */
-					elog(LOG, "Found LSN: %X/%X", (uint32) (res >> 32), (uint32) res);
+					elog(LOG, "Found prior LSN: %X/%X, it is used as stop LSN",
+						 (uint32) (res >> 32), (uint32) res);
 					return res;
 				}
 			}
@@ -1638,18 +1640,16 @@ wait_wal_lsn(XLogRecPtr lsn, bool is_start_lsn, bool wait_prev_lsn,
 				elog(INFO, "Wait for WAL segment %s to be archived",
 					 wal_segment_path);
 			else
-				elog(INFO, "Wait for LSN %s%X/%X in archived WAL segment %s",
-					 prior_to, (uint32) (lsn >> 32), (uint32) lsn,
-					 wal_segment_path);
+				elog(INFO, "Wait for LSN %X/%X in archived WAL segment %s",
+					 (uint32) (lsn >> 32), (uint32) lsn, wal_segment_path);
 		}
 
 		if (timeout > 0 && try_count > timeout)
 		{
 			if (file_exists)
 				elog(ERROR, "WAL segment %s was archived, "
-					 "but target LSN %s%X/%X could not be archived in %d seconds",
-					 wal_segment, prior_to, (uint32) (lsn >> 32), (uint32) lsn,
-					 timeout);
+					 "but target LSN %X/%X could not be archived in %d seconds",
+					 wal_segment, (uint32) (lsn >> 32), (uint32) lsn, timeout);
 			/* If WAL segment doesn't exist or we wait for previous segment */
 			else
 				elog(ERROR,
@@ -2056,7 +2056,6 @@ pg_stop_backup(pgBackup *backup)
 	{
 		char	   *xlog_path,
 					stream_xlog_path[MAXPGPATH];
-		XLogRecPtr	stop_valid_lsn = InvalidXLogRecPtr;
 
 		/* Wait for stop_lsn to be received by replica */
 		/* XXX Do we need this? */
@@ -2067,9 +2066,7 @@ pg_stop_backup(pgBackup *backup)
 		 * We wait for stop_lsn in stream mode just in case.
 		 */
 		if (!stop_lsn_exists)
-			stop_valid_lsn = wait_wal_lsn(stop_backup_lsn, false,
-										  !exclusive_backup && current.from_replica,
-										  false);
+			stop_backup_lsn = wait_wal_lsn(stop_backup_lsn, false, false);
 
 		if (stream_wal)
 		{
@@ -2088,7 +2085,7 @@ pg_stop_backup(pgBackup *backup)
 
 		/* iterate over WAL from stop_backup lsn to start_backup lsn */
 		if (!read_recovery_info(xlog_path, backup->tli, xlog_seg_size,
-								backup->start_lsn, stop_valid_lsn,
+								backup->start_lsn, stop_backup_lsn,
 								&backup->recovery_time, &backup->recovery_xid))
 		{
 			elog(LOG, "Failed to find Recovery Time in WAL. Forced to trust current_timestamp");