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Commit5fc1008

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Clean up temporary WAL segments after an instance crash
Temporary WAL segments are created in pg_wal and named as xlogtemp.pidbefore being renamed to the real deal when creating a new segment. Ifan instance crashes after the temporary segment is created and beforethe rename is done, then the server would finish with unremovable data.After an instance crash, scan pg_wal and remove any such segments. Withrepetitive unlucky crashes this would contribute to disk bloat andpresents risks of ENOSPC especially with max_wal_size close to themaximum allowed.Author: Michael PaquierReviewed-by: Yugo Nagata, Heikki LinnakangasDiscussion:https://postgr.es/m/20180514054955.GF1528@paquier.xyz
1 parent5e6e2c8 commit5fc1008

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1 file changed

+45
-7
lines changed
  • src/backend/access/transam

1 file changed

+45
-7
lines changed

‎src/backend/access/transam/xlog.c

Lines changed: 45 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -887,6 +887,7 @@ static bool WaitForWALToBecomeAvailable(XLogRecPtr RecPtr, bool randAccess,
887887
staticintemode_for_corrupt_record(intemode,XLogRecPtrRecPtr);
888888
staticvoidXLogFileClose(void);
889889
staticvoidPreallocXlogFiles(XLogRecPtrendptr);
890+
staticvoidRemoveTempXlogFiles(void);
890891
staticvoidRemoveOldXlogFiles(XLogSegNosegno,XLogRecPtrPriorRedoPtr,XLogRecPtrendptr);
891892
staticvoidRemoveXlogFile(constchar*segname,XLogRecPtrPriorRedoPtr,XLogRecPtrendptr);
892893
staticvoidUpdateLastRemovedPtr(char*filename);
@@ -3863,6 +3864,35 @@ UpdateLastRemovedPtr(char *filename)
38633864
SpinLockRelease(&XLogCtl->info_lck);
38643865
}
38653866

3867+
/*
3868+
* Remove all temporary log files in pg_wal
3869+
*
3870+
* This is called at the beginning of recovery after a previous crash,
3871+
* at a point where no other processes write fresh WAL data.
3872+
*/
3873+
staticvoid
3874+
RemoveTempXlogFiles(void)
3875+
{
3876+
DIR*xldir;
3877+
structdirent*xlde;
3878+
3879+
elog(DEBUG2,"removing all temporary WAL segments");
3880+
3881+
xldir=AllocateDir(XLOGDIR);
3882+
while ((xlde=ReadDir(xldir,XLOGDIR))!=NULL)
3883+
{
3884+
charpath[MAXPGPATH];
3885+
3886+
if (strncmp(xlde->d_name,"xlogtemp.",9)!=0)
3887+
continue;
3888+
3889+
snprintf(path,MAXPGPATH,XLOGDIR"/%s",xlde->d_name);
3890+
unlink(path);
3891+
elog(DEBUG2,"removed temporary WAL segment \"%s\"",path);
3892+
}
3893+
FreeDir(xldir);
3894+
}
3895+
38663896
/*
38673897
* Recycle or remove all log files older or equal to passed segno.
38683898
*
@@ -6379,17 +6409,25 @@ StartupXLOG(void)
63796409
*/
63806410
ValidateXLOGDirectoryStructure();
63816411

6382-
/*
6383-
* If we previously crashed, there might be data which we had written,
6384-
* intending to fsync it, but which we had not actually fsync'd yet.
6385-
* Therefore, a power failure in the near future might cause earlier
6386-
* unflushed writes to be lost, even though more recent data written to
6387-
* disk from here on would be persisted. To avoid that, fsync the entire
6388-
* data directory.
6412+
/*----------
6413+
* If we previously crashed, perform a couple of actions:
6414+
*- The pg_wal directory may still include some temporary WAL segments
6415+
* used when creating a new segment, so perform some clean up to not
6416+
* bloat this path. This is done first as there is no point to sync this
6417+
* temporary data.
6418+
*- There might be data which we had written, intending to fsync it,
6419+
* but which we had not actually fsync'd yet. Therefore, a power failure
6420+
* in the near future might cause earlier unflushed writes to be lost,
6421+
* even though more recent data written to disk from here on would be
6422+
* persisted. To avoid that, fsync the entire data directory.
6423+
*---------
63896424
*/
63906425
if (ControlFile->state!=DB_SHUTDOWNED&&
63916426
ControlFile->state!=DB_SHUTDOWNED_IN_RECOVERY)
6427+
{
6428+
RemoveTempXlogFiles();
63926429
SyncDataDirectory();
6430+
}
63936431

63946432
/*
63956433
* Initialize on the assumption we want to recover to the latest timeline

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