[Issue #115]: minor improvements

Author: gsmolk

src/backup.c

@@ -1528,22 +1528,22 @@ wait_wal_lsn(XLogRecPtr target_lsn, bool is_start_lsn, TimeLineID tli,
 			 * If we failed to get target LSN 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.
-			 * Note, that with NullOffset target_lsn we do not wait
+			 * Note, that with NullXRecOff target_lsn we do not wait
 			 * for 'timeout / 2' seconds before going for previous record,
 			 * because such LSN cannot be delivered at all.
 			 *
 			 * There are two cases for this:
 			 * 1. Replica returned readpoint LSN which just do not exists. We want to look
 			 *  for previous record in the same(!) WAL segment which endpoint points to this LSN.
-			 * 2. Replica returened endpoint LSN with 0 offset. We want to look
+			 * 2. Replica returened endpoint LSN with NullXRecOff. We want to look
 			 *  for previous record which endpoint points greater or equal LSN in previous WAL segment.
 			 */
 			if (current.from_replica &&
 				(XRecOffIsNull(target_lsn) || try_count > timeout / 2))
 			{
 				XLogRecPtr	res;
 
-				res = get_last_wal_lsn(wal_segment_dir, current.start_lsn, target_lsn, tli,
+				res = get_prior_record_lsn(wal_segment_dir, current.start_lsn, target_lsn, tli,
 									   in_prev_segment, instance_config.xlog_seg_size);
 
 				if (!XLogRecPtrIsInvalid(res))
@@ -1803,7 +1803,7 @@ pg_stop_backup(pgBackup *backup, PGconn *pg_startbackup_conn,
 
 		if (!XRecOffIsValid(stop_backup_lsn_tmp))
 		{
-			/* It is ok for replica to return STOP LSN with null offset */
+			/* It is ok for replica to return STOP LSN with NullXRecOff */
 			if (backup->from_replica && XRecOffIsNull(stop_backup_lsn_tmp))
 			{
 				char	   *xlog_path,
@@ -1820,7 +1820,7 @@ pg_stop_backup(pgBackup *backup, PGconn *pg_startbackup_conn,
 
 				/*
 				 * Note: even with gdb it is very hard to produce automated tests for
-				 * contrecord + null_offset STOP_LSN, so emulate it for manual testing.
+				 * contrecord + NullXRecOff, so emulate it for manual testing.
 				 */
 				//stop_backup_lsn_tmp = stop_backup_lsn_tmp - XLOG_SEG_SIZE;
 				//elog(WARNING, "New Invalid stop_backup_lsn value %X/%X",
@@ -1841,7 +1841,7 @@ pg_stop_backup(pgBackup *backup, PGconn *pg_startbackup_conn,
 				/*
 				 * Note, that there is no guarantee that corresponding WAL file even exists.
 				 * Replica may return LSN from future and keep staying in present.
-				 * Or it can return LSN with invalid XRecOff.
+				 * Or it can return LSN with NullXRecOff.
 				 *
 				 * That's bad, since we want to get real LSN to save it in backup label file
 				 * and to use it in WAL validation.
@@ -1851,17 +1851,16 @@ pg_stop_backup(pgBackup *backup, PGconn *pg_startbackup_conn,
 				 *	  look for the first valid record in it.
 				 * 	  It solves the problem of occasional invalid XRecOff on write-busy system.
 				 * 2. Failing that, look for record in previous segment with endpoint
-				 *	  equal or greater than stop_lsn. It may(!) solve the problem of 0 offset
+				 *	  equal or greater than stop_lsn. It may(!) solve the problem of NullXRecOff
 				 *	  on write-idle system. If that fails too, error out.
-				 * //TODO what kind of record that refers to?
 				 */
 
 				/* Wait for segment with current stop_lsn, it is ok for it to never arrive */
 				wait_wal_lsn(stop_backup_lsn_tmp, false, backup->tli,
 							false, true, WARNING, stream_wal);
 
 				/* Get the first record in segment with current stop_lsn */
-				lsn_tmp = get_first_wal_lsn(xlog_path, segno, backup->tli,
+				lsn_tmp = get_first_record_lsn(xlog_path, segno, backup->tli,
 										    instance_config.xlog_seg_size);
 
 				/* Check that returned LSN is valid and greater than stop_lsn */

src/parsexlog.c

@@ -529,13 +529,10 @@ wal_contains_lsn(const char *archivedir, XLogRecPtr target_lsn,
 }
 
 /*
- * Get LSN of first record within the WAL segment with number 'segno'.
- *
- * Returns LSN which points to end+1 of the last WAL record if seek_prev_segment
- * is true. Otherwise returns LSN of the record prior to stop_lsn.
+ * Get LSN of a first record within the WAL segment with number 'segno'.
  */
 XLogRecPtr
-get_first_wal_lsn(const char *archivedir, XLogSegNo	segno,
+get_first_record_lsn(const char *archivedir, XLogSegNo	segno,
 				 TimeLineID tli, uint32 wal_seg_size)
 {
 	XLogReaderState *xlogreader;
@@ -574,20 +571,18 @@ get_first_wal_lsn(const char *archivedir, XLogSegNo	segno,
 }
 
 /*
- * Get LSN of last or prior record within the WAL segment with number 'segno'.
- * If 'start_lsn'
- * is in the segment with number 'segno' then start from 'start_lsn', otherwise
- * start from offset 0 within the segment.
+ * Get LSN of a record prior to target_lsn.
+ * If 'start_lsn' is in the segment with number 'segno' then start from 'start_lsn',
+ * otherwise start from offset 0 within the segment.
  *
- * Returns LSN which points to end+1 of the last WAL record if seek_prev_segment
- * is true. Otherwise returns LSN of the record prior to stop_lsn.
+ * Returns LSN of a record which EndRecPtr is greater or equal to target_lsn.
+ * If 'seek_prev_segment' is true, then look for prior record in prior WAL segment.
  *
- * TODO Let's think of better function name.
  * it's unclear that "last" in "last_wal_lsn" refers to the
  * "closest to stop_lsn backward or forward, depending on seek_prev_segment setting".
  */
 XLogRecPtr
-get_last_wal_lsn(const char *archivedir, XLogRecPtr start_lsn,
+get_prior_record_lsn(const char *archivedir, XLogRecPtr start_lsn,
 				 XLogRecPtr stop_lsn, TimeLineID tli, bool seek_prev_segment,
 				 uint32 wal_seg_size)
 {

src/pg_probackup.h

@@ -711,11 +711,11 @@ extern bool read_recovery_info(const char *archivedir, TimeLineID tli,
 							   TransactionId *recovery_xid);
 extern bool wal_contains_lsn(const char *archivedir, XLogRecPtr target_lsn,
 							 TimeLineID target_tli, uint32 seg_size);
-extern XLogRecPtr get_last_wal_lsn(const char *archivedir, XLogRecPtr start_lsn,
+extern XLogRecPtr get_prior_record_lsn(const char *archivedir, XLogRecPtr start_lsn,
 								   XLogRecPtr stop_lsn, TimeLineID tli,
 								   bool seek_prev_segment, uint32 seg_size);
 
-extern XLogRecPtr get_first_wal_lsn(const char *archivedir, XLogRecPtr start_lsn,
+extern XLogRecPtr get_first_record_lsn(const char *archivedir, XLogRecPtr start_lsn,
 									TimeLineID tli, uint32 wal_seg_size);
 
 /* in util.c */