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Fix failure to guarantee that a checkpoint will write out pg_clog updates

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for transaction commits that occurred just before the checkpoint.  This is
an EXTREMELY serious bug --- kudos to Satoshi Okada for creating a
reproducible test case to prove its existence.
This commit is contained in:
Tom Lane
2004-08-11 04:08:02 +00:00
parent a1dd58e509
commit d508e0ddd2
3 changed files with 47 additions and 10 deletions
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36
src/backend/access/transam/xact.c
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@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/access/transam/xact.c,v 1.156 2003/10/16 16:50:41 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/access/transam/xact.c,v 1.156.2.1 2004/08/11 04:08:00 tgl Exp $
*
* NOTES
* Transaction aborts can now occur two ways:
@@ -503,6 +503,7 @@ RecordTransactionCommit(void)
if (MyXactMadeXLogEntry || MyXactMadeTempRelUpdate)
{
TransactionId xid = GetCurrentTransactionId();
bool madeTCentries;
XLogRecPtr recptr;
/* Tell bufmgr and smgr to prepare for commit */
@@ -511,12 +512,29 @@ RecordTransactionCommit(void)
START_CRIT_SECTION();
/*
* We only need to log the commit in xlog if the transaction made
* any transaction-controlled XLOG entries. (Otherwise, its XID
* appears nowhere in permanent storage, so no one else will ever
* care if it committed.)
* If our transaction made any transaction-controlled XLOG entries,
* we need to lock out checkpoint start between writing our XLOG
* record and updating pg_clog. Otherwise it is possible for the
* checkpoint to set REDO after the XLOG record but fail to flush the
* pg_clog update to disk, leading to loss of the transaction commit
* if we crash a little later. Slightly klugy fix for problem
* discovered 2004-08-10.
*
* (If it made no transaction-controlled XLOG entries, its XID
* appears nowhere in permanent storage, so no one else will ever care
* if it committed; so it doesn't matter if we lose the commit flag.)
*
* Note we only need a shared lock.
*/
if (MyLastRecPtr.xrecoff != 0)
madeTCentries = (MyLastRecPtr.xrecoff != 0);
if (madeTCentries)
LWLockAcquire(CheckpointStartLock, LW_SHARED);
/*
* We only need to log the commit in XLOG if the transaction made
* any transaction-controlled XLOG entries.
*/
if (madeTCentries)
{
/* Need to emit a commit record */
XLogRecData rdata;
@@ -585,6 +603,10 @@ RecordTransactionCommit(void)
if (MyLastRecPtr.xrecoff != 0 || MyXactMadeTempRelUpdate)
TransactionIdCommit(xid);
/* Unlock checkpoint lock if we acquired it */
if (madeTCentries)
LWLockRelease(CheckpointStartLock);
END_CRIT_SECTION();
}
@@ -698,6 +720,8 @@ RecordTransactionAbort(void)
* care if it committed.) We do not flush XLOG to disk in any
* case, since the default assumption after a crash would be that
* we aborted, anyway.
* For the same reason, we don't need to worry about interlocking
* against checkpoint start.
*/
if (MyLastRecPtr.xrecoff != 0)
{