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Fix recovery of 2PC transaction during crash recovery 

A crash in the middle of a checkpoint with some two-phase state data
already flushed to disk by this checkpoint could cause a follow-up crash
recovery to recover twice the same transaction, once from what has been
found in pg_twophase/ at the beginning of recovery and a second time
when replaying its corresponding record.

This would lead to FATAL failures in the startup process during
recovery, where the same transaction would have a state recovered twice
instead of once:
LOG:  recovering prepared transaction 731 from shared memory
LOG:  recovering prepared transaction 731 from shared memory
FATAL:  lock ExclusiveLock on object 731/0/0 is already held

This issue is fixed by skipping the addition of any 2PC state coming
from a record whose equivalent 2PC state file has already been loaded in
TwoPhaseState at the beginning of recovery by restoreTwoPhaseData(),
which is OK as long as the system has not reached a consistent state.

The timing to get a messed up recovery processing is very racy, and
would very unlikely happen.  The thread that has reported the issue has
demonstrated the bug using injection points to force a PANIC in the
middle of a checkpoint.

Issue introduced in 728bd99, so backpatch all the way down.

Reported-by: "suyu.cmj" <mengjuan.cmj@alibaba-inc.com>
Author: "suyu.cmj" <mengjuan.cmj@alibaba-inc.com>
Author: Michael Paquier
Discussion: https://postgr.es/m/109e6994-b971-48cb-84f6-829646f18b4c.mengjuan.cmj@alibaba-inc.com
Backpatch-through: 11
This commit is contained in:
Michael Paquier 2023-07-18 13:43:44 +09:00
parent 8fab4b3480
commit cb0cca1880
1 changed files with 33 additions and 0 deletions
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33
src/backend/access/transam/twophase.c
View File

@ -86,6 +86,7 @@
#include "access/xlog.h"
#include "access/xloginsert.h"
#include "access/xlogreader.h"
#include "access/xlogrecovery.h"
#include "access/xlogutils.h"
#include "catalog/pg_type.h"
#include "catalog/storage.h"
@ -2477,6 +2478,38 @@ PrepareRedoAdd(char *buf, XLogRecPtr start_lsn,
* that it got added in the redo phase
*/
/*
* In the event of a crash while a checkpoint was running, it may be
* possible that some two-phase data found its way to disk while its
* corresponding record needs to be replayed in the follow-up recovery.
* As the 2PC data was on disk, it has already been restored at the
* beginning of recovery with restoreTwoPhaseData(), so skip this record
* to avoid duplicates in TwoPhaseState. If a consistent state has been
* reached, the record is added to TwoPhaseState and it should have no
* corresponding file in pg_twophase.
*/
if (!XLogRecPtrIsInvalid(start_lsn))
{
char path[MAXPGPATH];
TwoPhaseFilePath(path, hdr->xid);
if (access(path, F_OK) == 0)
{
ereport(reachedConsistency ? ERROR : WARNING,
(errmsg("could not recover two-phase state file for transaction %u",
hdr->xid),
errdetail("Two-phase state file has been found in WAL record %X/%X, but this transaction has already been restored from disk.",
LSN_FORMAT_ARGS(start_lsn))));
return;
}
if (errno != ENOENT)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not access file \"%s\": %m", path)));
}
/* Get a free gxact from the freelist */
if (TwoPhaseState->freeGXacts == NULL)
ereport(ERROR,