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Whoops, I was a tad too enthusiastic about using shared lock mode for

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SInvalLock.  GetSnapshotData(true) has to use exclusive lock, since
it sets MyProc->xmin.
This commit is contained in:
Tom Lane
2001-09-29 15:29:48 +00:00
parent 6fdf7bed60
commit 2a314add00
1 changed files with 13 additions and 8 deletions
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21
src/backend/storage/ipc/sinval.c
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@ -8,7 +8,7 @@
* *
* *
* IDENTIFICATION * IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/storage/ipc/sinval.c,v 1.41 2001/09/29 04:02:24 tgl Exp $ * $Header: /cvsroot/pgsql/src/backend/storage/ipc/sinval.c,v 1.42 2001/09/29 15:29:48 tgl Exp $
* *
*------------------------------------------------------------------------- *-------------------------------------------------------------------------
*/ */
@ -310,19 +310,24 @@ GetSnapshotData(bool serializable)
if (snapshot == NULL) if (snapshot == NULL)
elog(ERROR, "Memory exhausted in GetSnapshotData"); elog(ERROR, "Memory exhausted in GetSnapshotData");
snapshot->xmin = GetCurrentTransactionId();
LWLockAcquire(SInvalLock, LW_SHARED);
/* /*
* There can be no more than lastBackend active transactions, so this * Allocating space for MaxBackends xids is usually overkill;
* is enough space: * lastBackend would be sufficient. But it seems better to do the
* malloc while not holding the lock, so we can't look at lastBackend.
*/ */
snapshot->xip = (TransactionId *) snapshot->xip = (TransactionId *)
malloc(segP->lastBackend * sizeof(TransactionId)); malloc(MaxBackends * sizeof(TransactionId));
if (snapshot->xip == NULL) if (snapshot->xip == NULL)
elog(ERROR, "Memory exhausted in GetSnapshotData"); elog(ERROR, "Memory exhausted in GetSnapshotData");
snapshot->xmin = GetCurrentTransactionId();
/*
* If we are going to set MyProc->xmin then we'd better get exclusive
* lock; if not, this is a read-only operation so it can be shared.
*/
LWLockAcquire(SInvalLock, serializable ? LW_EXCLUSIVE : LW_SHARED);
/*-------------------- /*--------------------
* Unfortunately, we have to call ReadNewTransactionId() after acquiring * Unfortunately, we have to call ReadNewTransactionId() after acquiring
* SInvalLock above. It's not good because ReadNewTransactionId() does * SInvalLock above. It's not good because ReadNewTransactionId() does