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Update minimum recovery point on truncation.

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If a file is truncated, we must update minRecoveryPoint. Once a file is
truncated, there's no going back; it would not be safe to stop recovery
at 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.
This commit is contained in:
Heikki Linnakangas
2012-12-10 15:54:42 +02:00
parent 6be799664a
commit 7bffc9b7bf
2 changed files with 50 additions and 11 deletions
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29
src/backend/access/transam/xact.c
View File

@@ -4617,6 +4617,25 @@ xact_redo_commit_internal(TransactionId xid, XLogRecPtr lsn,
}
/* Make sure files supposed to be dropped are dropped */
if (nrels > 0)
{
/*
* First update minimum recovery point to cover this WAL record. Once
* a relation is deleted, there's no going back. The buffer manager
* enforces the WAL-first rule for normal updates to relation files,
* so that the minimum recovery point is always updated before the
* corresponding change in the data file is flushed to disk, but we
* have to do the same here since we're bypassing the buffer manager.
*
* Doing this before deleting the files means that if a deletion fails
* for some reason, you cannot start up the system even after restart,
* until you fix the underlying situation so that the deletion will
* succeed. Alternatively, we could update the minimum recovery point
* after deletion, but that would leave a small window where the
* WAL-first rule would be violated.
*/
XLogFlush(lsn);
for (i = 0; i < nrels; i++)
{
SMgrRelation srel = smgropen(xnodes[i], InvalidBackendId);
@@ -4627,13 +4646,15 @@ xact_redo_commit_internal(TransactionId xid, XLogRecPtr lsn,
smgrdounlink(srel, true);
smgrclose(srel);
}
}
/*
* We issue an XLogFlush() for the same reason we emit ForceSyncCommit()
* in normal operation. For example, in DROP DATABASE, we delete all the
* files belonging to the database, and then commit the transaction. If we
* crash after all the files have been deleted but before the commit, you
* have an entry in pg_database without any files. To minimize the window
* in normal operation. For example, in CREATE DATABASE, we copy all files
* from the template database, and then commit the transaction. If we
* crash after all the files have been copied but before the commit, you
* have files in the data directory without an entry in pg_database. To
* minimize the window
* for that, we use ForceSyncCommit() to rush the commit record to disk as
* quick as possible. We have the same window during recovery, and forcing
* an XLogFlush() (which updates minRecoveryPoint during recovery) helps

18
src/backend/catalog/storage.c
View File

@@ -482,6 +482,24 @@ smgr_redo(XLogRecPtr lsn, XLogRecord *record)
*/
smgrcreate(reln, MAIN_FORKNUM, true);
/*
* Before we perform the truncation, update minimum recovery point
* to cover this WAL record. Once the relation is truncated, there's
* no going back. The buffer manager enforces the WAL-first rule
* for normal updates to relation files, so that the minimum recovery
* point is always updated before the corresponding change in the
* data file is flushed to disk. We have to do the same manually
* here.
*
* Doing this before the truncation means that if the truncation fails
* for some reason, you cannot start up the system even after restart,
* until you fix the underlying situation so that the truncation will
* succeed. Alternatively, we could update the minimum recovery point
* after truncation, but that would leave a small window where the
* WAL-first rule could be violated.
*/
XLogFlush(lsn);
smgrtruncate(reln, MAIN_FORKNUM, xlrec->blkno);
/* Also tell xlogutils.c about it */