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Commit6d8096e

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When two base backups are started at the same time with pg_basebackup,
ensure that they use different checkpoints as the starting point. We usethe checkpoint redo location as a unique identifier for the base backup inthe end-of-backup record, and in the backup history file name.Bug spotted by Fujii Masao.
1 parent62bf9c2 commit6d8096e

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1 file changed

+61
-34
lines changed
  • src/backend/access/transam

1 file changed

+61
-34
lines changed

‎src/backend/access/transam/xlog.c

Lines changed: 61 additions & 34 deletions
Original file line numberDiff line numberDiff line change
@@ -355,10 +355,13 @@ typedef struct XLogCtlInsert
355355
* exclusiveBackup is true if a backup started with pg_start_backup() is
356356
* in progress, and nonExclusiveBackups is a counter indicating the number
357357
* of streaming base backups currently in progress. forcePageWrites is
358-
* set to true when either of these is non-zero.
358+
* set to true when either of these is non-zero. lastBackupStart is the
359+
* latest checkpoint redo location used as a starting point for an online
360+
* backup.
359361
*/
360362
boolexclusiveBackup;
361363
intnonExclusiveBackups;
364+
XLogRecPtrlastBackupStart;
362365
}XLogCtlInsert;
363366

364367
/*
@@ -8808,6 +8811,19 @@ do_pg_start_backup(const char *backupidstr, bool fast, char **labelfile)
88088811
errmsg("backup label too long (max %d bytes)",
88098812
MAXPGPATH)));
88108813

8814+
/*
8815+
* Force an XLOG file switch before the checkpoint, to ensure that the WAL
8816+
* segment the checkpoint is written to doesn't contain pages with old
8817+
* timeline IDs. That would otherwise happen if you called
8818+
* pg_start_backup() right after restoring from a PITR archive: the first
8819+
* WAL segment containing the startup checkpoint has pages in the
8820+
* beginning with the old timeline ID. That can cause trouble at recovery:
8821+
* we won't have a history file covering the old timeline if pg_xlog
8822+
* directory was not included in the base backup and the WAL archive was
8823+
* cleared too before starting the backup.
8824+
*/
8825+
RequestXLogSwitch();
8826+
88118827
/*
88128828
* Mark backup active in shared memory. We must do full-page WAL writes
88138829
* during an on-line backup even if not doing so at other times, because
@@ -8843,43 +8859,54 @@ do_pg_start_backup(const char *backupidstr, bool fast, char **labelfile)
88438859
XLogCtl->Insert.forcePageWrites= true;
88448860
LWLockRelease(WALInsertLock);
88458861

8846-
/*
8847-
* Force an XLOG file switch before the checkpoint, to ensure that the WAL
8848-
* segment the checkpoint is written to doesn't contain pages with old
8849-
* timeline IDs. That would otherwise happen if you called
8850-
* pg_start_backup() right after restoring from a PITR archive: the first
8851-
* WAL segment containing the startup checkpoint has pages in the
8852-
* beginning with the old timeline ID. That can cause trouble at recovery:
8853-
* we won't have a history file covering the old timeline if pg_xlog
8854-
* directory was not included in the base backup and the WAL archive was
8855-
* cleared too before starting the backup.
8856-
*/
8857-
RequestXLogSwitch();
8858-
88598862
/* Ensure we release forcePageWrites if fail below */
88608863
PG_ENSURE_ERROR_CLEANUP(pg_start_backup_callback, (Datum)BoolGetDatum(exclusive));
88618864
{
8862-
/*
8863-
* Force a CHECKPOINT.Aside from being necessary to prevent torn
8864-
* page problems, this guarantees that two successive backup runs will
8865-
* have different checkpoint positions and hence different history
8866-
* file names, even if nothing happened in between.
8867-
*
8868-
* We use CHECKPOINT_IMMEDIATE only if requested by user (via passing
8869-
* fast = true). Otherwise this can take awhile.
8870-
*/
8871-
RequestCheckpoint(CHECKPOINT_FORCE |CHECKPOINT_WAIT |
8872-
(fast ?CHECKPOINT_IMMEDIATE :0));
8865+
boolgotUniqueStartpoint= false;
8866+
do
8867+
{
8868+
/*
8869+
* Force a CHECKPOINT.Aside from being necessary to prevent torn
8870+
* page problems, this guarantees that two successive backup runs will
8871+
* have different checkpoint positions and hence different history
8872+
* file names, even if nothing happened in between.
8873+
*
8874+
* We use CHECKPOINT_IMMEDIATE only if requested by user (via passing
8875+
* fast = true). Otherwise this can take awhile.
8876+
*/
8877+
RequestCheckpoint(CHECKPOINT_FORCE |CHECKPOINT_WAIT |
8878+
(fast ?CHECKPOINT_IMMEDIATE :0));
88738879

8874-
/*
8875-
* Now we need to fetch the checkpoint record location, and also its
8876-
* REDO pointer. The oldest point in WAL that would be needed to
8877-
* restore starting from the checkpoint is precisely the REDO pointer.
8878-
*/
8879-
LWLockAcquire(ControlFileLock,LW_SHARED);
8880-
checkpointloc=ControlFile->checkPoint;
8881-
startpoint=ControlFile->checkPointCopy.redo;
8882-
LWLockRelease(ControlFileLock);
8880+
/*
8881+
* Now we need to fetch the checkpoint record location, and also its
8882+
* REDO pointer. The oldest point in WAL that would be needed to
8883+
* restore starting from the checkpoint is precisely the REDO pointer.
8884+
*/
8885+
LWLockAcquire(ControlFileLock,LW_SHARED);
8886+
checkpointloc=ControlFile->checkPoint;
8887+
startpoint=ControlFile->checkPointCopy.redo;
8888+
LWLockRelease(ControlFileLock);
8889+
8890+
/*
8891+
* If two base backups are started at the same time (in WAL
8892+
* sender processes), we need to make sure that they use
8893+
* different checkpoints as starting locations, because we use
8894+
* the starting WAL location as a unique identifier for the base
8895+
* backup in the end-of-backup WAL record and when we write the
8896+
* backup history file. Perhaps it would be better generate a
8897+
* separate unique ID for each backup instead of forcing another
8898+
* checkpoint, but taking a checkpoint right after another is
8899+
* not that expensive either because only few buffers have been
8900+
* dirtied yet.
8901+
*/
8902+
LWLockAcquire(WALInsertLock,LW_SHARED);
8903+
if (XLByteLT(XLogCtl->Insert.lastBackupStart,startpoint))
8904+
{
8905+
XLogCtl->Insert.lastBackupStart=startpoint;
8906+
gotUniqueStartpoint= true;
8907+
}
8908+
LWLockRelease(WALInsertLock);
8909+
}while(!gotUniqueStartpoint);
88838910

88848911
XLByteToSeg(startpoint,_logId,_logSeg);
88858912
XLogFileName(xlogfilename,ThisTimeLineID,_logId,_logSeg);

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