Matt Newell <newellm@blur.com> writes:
> Patch attached works great. I added the dboid to the QueueBackendStatus
> struct but that might not be needed if there is an easy and fast way to get a
> db oid from a backend pid.
Not particularly; I agree with adding it to this data structure. One
reason is it makes the array stride a power of 2, so array accesses may be
a shade cheaper than before.
> I also skip the max pos calculation loop if QUEUE_HEAD is on the same page as
> QUEUE_TAIL, with the thought that it's not desirable to increase the time that
> AsyncQueueLock is held if the queue is small and
> asyncQueueReadAllNotifications will execute quickly.
Check.
There were a couple of minor bugs in this, but I fixed them and committed
it.
> I then noticed that we are taking the same lock twice in a row to read the
> same values, first in Exec_ListenPreCommit then in
> asyncQueueReadAllNotifications, and much of the time the latter will simply
> return because pos will already be at QUEUE_HEAD. I prepared a second patch
> that splits asyncQueueReadAllNotifications. Exec_ListPreCommit then only calls
> the worker version only when needed. This avoids the duplicate lock.
I was unimpressed with this; the refactoring of asyncQueueReadAllNotifications
seemed messy and definitely was undocumented. I think the main actual
value is to skip doing anything during Exec_ListenPreCommit when
max == head, so I extracted that part and included it.
regards, tom lane
