diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/backend/storage/ipc/procarray.c | 16 |
1 files changed, 8 insertions, 8 deletions
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c index 6eb7c72ec32..a7e8cf2d43a 100644 --- a/src/backend/storage/ipc/procarray.c +++ b/src/backend/storage/ipc/procarray.c @@ -2096,20 +2096,21 @@ GetOldestActiveTransactionId(void) Assert(!RecoveryInProgress()); - LWLockAcquire(ProcArrayLock, LW_SHARED); - /* - * It's okay to read nextXid without acquiring XidGenLock because (1) we - * assume TransactionIds can be read atomically and (2) we don't care if - * we get a slightly stale value. It can't be very stale anyway, because - * the LWLockAcquire above will have done any necessary memory - * interlocking. + * Read nextXid, as the upper bound of what's still active. + * + * Reading a TransactionId is atomic, but we must grab the lock to make + * sure that all XIDs < nextXid are already present in the proc array (or + * have already completed), when we spin over it. */ + LWLockAcquire(XidGenLock, LW_SHARED); oldestRunningXid = ShmemVariableCache->nextXid; + LWLockRelease(XidGenLock); /* * Spin over procArray collecting all xids and subxids. */ + LWLockAcquire(ProcArrayLock, LW_SHARED); for (index = 0; index < arrayP->numProcs; index++) { int pgprocno = arrayP->pgprocnos[index]; @@ -2131,7 +2132,6 @@ GetOldestActiveTransactionId(void) * smaller than oldestRunningXid */ } - LWLockRelease(ProcArrayLock); return oldestRunningXid; |