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Additional test for each commit in sync rep path to plug minute

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possibility of race condition that would effect performance only.
Requested by Robert Haas. Re-arrange related comments.
This commit is contained in:
Simon Riggs 2011-03-26 10:09:37 +00:00
parent bfa4440ca5
commit 92f4786fa9
1 changed files with 18 additions and 11 deletions
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29
src/backend/replication/syncrep.c
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@ -114,21 +114,28 @@ SyncRepWaitForLSN(XLogRecPtr XactCommitLSN)
/* Reset the latch before adding ourselves to the queue. */
ResetLatch(&MyProc->waitLatch);
LWLockAcquire(SyncRepLock, LW_EXCLUSIVE);
Assert(MyProc->syncRepState == SYNC_REP_NOT_WAITING);
/*
* We don't wait for sync rep if WalSndCtl->sync_standbys_defined is
* not set. See SyncRepUpdateSyncStandbysDefined.
*
* Also check that the standby hasn't already replied. Unlikely
* race condition but we'll be fetching that cache line anyway
* so its likely to be a low cost check.
*/
if (!WalSndCtl->sync_standbys_defined ||
XLByteLE(XactCommitLSN, WalSndCtl->lsn))
{
LWLockRelease(SyncRepLock);
return;
}
/*
* Set our waitLSN so WALSender will know when to wake us, and add
* ourselves to the queue.
*/
LWLockAcquire(SyncRepLock, LW_EXCLUSIVE);
Assert(MyProc->syncRepState == SYNC_REP_NOT_WAITING);
if (!WalSndCtl->sync_standbys_defined)
{
/*
* We don't wait for sync rep if WalSndCtl->sync_standbys_defined is
* not set. See SyncRepUpdateSyncStandbysDefined.
*/
LWLockRelease(SyncRepLock);
return;
}
MyProc->waitLSN = XactCommitLSN;
MyProc->syncRepState = SYNC_REP_WAITING;
SyncRepQueueInsert();