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Commitfbe285a

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Update minimum recovery point on truncation.
If a file is truncated, we must update minRecoveryPoint. Once a file istruncated, there's no going back; it would not be safe to stop recoveryat a point earlier than that anymore.Per report from Kyotaro HORIGUCHI. Backpatch to 8.4. Before that,minRecoveryPoint was not updated during recovery at all.
1 parent6cb8c60 commitfbe285a

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2 files changed

+50
-11
lines changed

2 files changed

+50
-11
lines changed

‎src/backend/access/transam/xact.c

Lines changed: 32 additions & 11 deletions
Original file line numberDiff line numberDiff line change
@@ -4637,23 +4637,44 @@ xact_redo_commit_internal(TransactionId xid, XLogRecPtr lsn,
46374637
}
46384638

46394639
/* Make sure files supposed to be dropped are dropped */
4640-
for (i=0;i<nrels;i++)
4640+
if (nrels>0)
46414641
{
4642-
SMgrRelationsrel=smgropen(xnodes[i],InvalidBackendId);
4643-
ForkNumberfork;
4642+
/*
4643+
* First update minimum recovery point to cover this WAL record. Once
4644+
* a relation is deleted, there's no going back. The buffer manager
4645+
* enforces the WAL-first rule for normal updates to relation files,
4646+
* so that the minimum recovery point is always updated before the
4647+
* corresponding change in the data file is flushed to disk, but we
4648+
* have to do the same here since we're bypassing the buffer manager.
4649+
*
4650+
* Doing this before deleting the files means that if a deletion fails
4651+
* for some reason, you cannot start up the system even after restart,
4652+
* until you fix the underlying situation so that the deletion will
4653+
* succeed. Alternatively, we could update the minimum recovery point
4654+
* after deletion, but that would leave a small window where the
4655+
* WAL-first rule would be violated.
4656+
*/
4657+
XLogFlush(lsn);
46444658

4645-
for (fork=0;fork <=MAX_FORKNUM;fork++)
4646-
XLogDropRelation(xnodes[i],fork);
4647-
smgrdounlink(srel, true);
4648-
smgrclose(srel);
4659+
for (i=0;i<nrels;i++)
4660+
{
4661+
SMgrRelationsrel=smgropen(xnodes[i],InvalidBackendId);
4662+
ForkNumberfork;
4663+
4664+
for (fork=0;fork <=MAX_FORKNUM;fork++)
4665+
XLogDropRelation(xnodes[i],fork);
4666+
smgrdounlink(srel, true);
4667+
smgrclose(srel);
4668+
}
46494669
}
46504670

46514671
/*
46524672
* We issue an XLogFlush() for the same reason we emit ForceSyncCommit()
4653-
* in normal operation. For example, in DROP DATABASE, we delete all the
4654-
* files belonging to the database, and then commit the transaction. If we
4655-
* crash after all the files have been deleted but before the commit, you
4656-
* have an entry in pg_database without any files. To minimize the window
4673+
* in normal operation. For example, in CREATE DATABASE, we copy all files
4674+
* from the template database, and then commit the transaction. If we
4675+
* crash after all the files have been copied but before the commit, you
4676+
* have files in the data directory without an entry in pg_database. To
4677+
* minimize the window
46574678
* for that, we use ForceSyncCommit() to rush the commit record to disk as
46584679
* quick as possible. We have the same window during recovery, and forcing
46594680
* an XLogFlush() (which updates minRecoveryPoint during recovery) helps

‎src/backend/catalog/storage.c

Lines changed: 18 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -505,6 +505,24 @@ smgr_redo(XLogRecPtr lsn, XLogRecord *record)
505505
*/
506506
smgrcreate(reln,MAIN_FORKNUM, true);
507507

508+
/*
509+
* Before we perform the truncation, update minimum recovery point
510+
* to cover this WAL record. Once the relation is truncated, there's
511+
* no going back. The buffer manager enforces the WAL-first rule
512+
* for normal updates to relation files, so that the minimum recovery
513+
* point is always updated before the corresponding change in the
514+
* data file is flushed to disk. We have to do the same manually
515+
* here.
516+
*
517+
* Doing this before the truncation means that if the truncation fails
518+
* for some reason, you cannot start up the system even after restart,
519+
* until you fix the underlying situation so that the truncation will
520+
* succeed. Alternatively, we could update the minimum recovery point
521+
* after truncation, but that would leave a small window where the
522+
* WAL-first rule could be violated.
523+
*/
524+
XLogFlush(lsn);
525+
508526
smgrtruncate(reln,MAIN_FORKNUM,xlrec->blkno);
509527

510528
/* Also tell xlogutils.c about it */

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