opensourcemirror
/
postgresql
mirror of git://git.postgresql.org/git/postgresql.git
1
0
Fork 0
Code Issues Releases Wiki Activity

Clarify what is protected by WaitLSNLock 

Not just WaitLSNState.waitersHeap, but also WaitLSNState.procInfos and
updating of WaitLSNState.minWaitedLSN is protected by WaitLSNLock.  There
is one now documented exclusion on fast-path checking of
WaitLSNProcInfo.inHeap flag.

Discussion: https://postgr.es/m/202404030658.hhj3vfxeyhft%40alvherre.pgsql
This commit is contained in:
Alexander Korotkov 2024-04-07 00:32:35 +03:00
parent 25f42429e2
commit ee79928441
2 changed files with 13 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
src/backend/commands/waitlsn.c
View File

@ -109,13 +109,13 @@ addLSNWaiter(XLogRecPtr lsn)
{
WaitLSNProcInfo *procInfo = &waitLSN->procInfos[MyProcNumber];
LWLockAcquire(WaitLSNLock, LW_EXCLUSIVE);
Assert(!procInfo->inHeap);
procInfo->procnum = MyProcNumber;
procInfo->waitLSN = lsn;
LWLockAcquire(WaitLSNLock, LW_EXCLUSIVE);
pairingheap_add(&waitLSN->waitersHeap, &procInfo->phNode);
procInfo->inHeap = true;
updateMinWaitedLSN();
@ -203,6 +203,12 @@ WaitLSNSetLatches(XLogRecPtr currentLSN)
void
WaitLSNCleanup(void)
{
/*
* We do a fast-path check of the 'inHeap' flag without the lock. This
* flag is set to true only by the process itself. So, it's only possible
* to get a false positive. But that will be eliminated by a recheck
* inside deleteLSNWaiter().
*/
if (waitLSN->procInfos[MyProcNumber].inHeap)
deleteLSNWaiter();
}

7
src/include/commands/waitlsn.h
View File

@ -49,7 +49,7 @@ typedef struct WaitLSNState
/*
* The minimum LSN value some process is waiting for. Used for the
* fast-path checking if we need to wake up any waiters after replaying a
* WAL record.
* WAL record. Could be read lock-less. Update protected by WaitLSNLock.
*/
pg_atomic_uint64 minWaitedLSN;
@ -59,7 +59,10 @@ typedef struct WaitLSNState
*/
pairingheap waitersHeap;
/* An array with per-process information, indexed by the process number */
/*
* An array with per-process information, indexed by the process number.
* Protected by WaitLSNLock.
*/
WaitLSNProcInfo procInfos[FLEXIBLE_ARRAY_MEMBER];
} WaitLSNState;