diff options
Diffstat (limited to 'src/backend/commands/async.c')
| -rw-r--r-- | src/backend/commands/async.c | 37 |
1 files changed, 27 insertions, 10 deletions
diff --git a/src/backend/commands/async.c b/src/backend/commands/async.c index 71b7577afc0..4c1286eb988 100644 --- a/src/backend/commands/async.c +++ b/src/backend/commands/async.c @@ -244,19 +244,22 @@ typedef struct QueueBackendStatus /* * Shared memory state for LISTEN/NOTIFY (excluding its SLRU stuff) * - * The AsyncQueueControl structure is protected by the NotifyQueueLock. + * The AsyncQueueControl structure is protected by the NotifyQueueLock and + * NotifyQueueTailLock. * - * When holding the lock in SHARED mode, backends may only inspect their own - * entries as well as the head and tail pointers. Consequently we can allow a - * backend to update its own record while holding only SHARED lock (since no - * other backend will inspect it). + * When holding NotifyQueueLock in SHARED mode, backends may only inspect + * their own entries as well as the head and tail pointers. Consequently we + * can allow a backend to update its own record while holding only SHARED lock + * (since no other backend will inspect it). * - * When holding the lock in EXCLUSIVE mode, backends can inspect the entries - * of other backends and also change the head and tail pointers. + * When holding NotifyQueueLock in EXCLUSIVE mode, backends can inspect the + * entries of other backends and also change the head pointer. When holding + * both NotifyQueueLock and NotifyQueueTailLock in EXCLUSIVE mode, backends + * can change the tail pointer. * * NotifySLRULock is used as the control lock for the pg_notify SLRU buffers. - * In order to avoid deadlocks, whenever we need both locks, we always first - * get NotifyQueueLock and then NotifySLRULock. + * In order to avoid deadlocks, whenever we need multiple locks, we first get + * NotifyQueueTailLock, then NotifyQueueLock, and lastly NotifySLRULock. * * Each backend uses the backend[] array entry with index equal to its * BackendId (which can range from 1 to MaxBackends). We rely on this to make @@ -2177,6 +2180,10 @@ asyncQueueAdvanceTail(void) int newtailpage; int boundary; + /* Restrict task to one backend per cluster; see SimpleLruTruncate(). */ + LWLockAcquire(NotifyQueueTailLock, LW_EXCLUSIVE); + + /* Compute the new tail. */ LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE); min = QUEUE_HEAD; for (BackendId i = QUEUE_FIRST_LISTENER; i > 0; i = QUEUE_NEXT_LISTENER(i)) @@ -2185,7 +2192,6 @@ asyncQueueAdvanceTail(void) min = QUEUE_POS_MIN(min, QUEUE_BACKEND_POS(i)); } oldtailpage = QUEUE_POS_PAGE(QUEUE_TAIL); - QUEUE_TAIL = min; LWLockRelease(NotifyQueueLock); /* @@ -2205,6 +2211,17 @@ asyncQueueAdvanceTail(void) */ SimpleLruTruncate(NotifyCtl, newtailpage); } + + /* + * Advertise the new tail. This changes asyncQueueIsFull()'s verdict for + * the segment immediately prior to the new tail, allowing fresh data into + * that segment. + */ + LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE); + QUEUE_TAIL = min; + LWLockRelease(NotifyQueueLock); + + LWLockRelease(NotifyQueueTailLock); } /* |