On Mon, May 11, 2015 at 09:19:43AM +0800, King Cao wrote:
> > > Suppose transport->pending is 1, so the value of need is 2 (pending+1),
> >
> > Which means that we're in the process of making an asynchronous
> > connection to the transport to request a delivery.
> >
> > > queue->window is 5 by default (initial destination concurrency). Suppose
> > > there is one todo entry and one busy entry, so min(queue->window -
> > > queue->busy_refcount, queue->todo_refcount) is 1, which cause the
> > > invalidation of if statement. So even there is one todo entry, but this
> > > queue is still not satisfied.
> >
> > That's correct, the todo entry will be allocated to the pending
> > connection when it completes.
> >
> > > PS: QMGR_TRANSPORT_MAX_PEND has changed from 1 to 2 before, not sure if
> > > it's side-effect of this change.
> >
> > To allow for more than one pending connection at a time, which
> > improves queue manager throughput under extreme message rates
> > (thousands per second, when benchmarking with RAM-disk queues).
> >
> > The code is correct.
>
> The weird thing is that if queue->todo_refcount = 2, the queue will be
> satisfied but if queue->todo_refcount = 1, the queue is not satisfied. So
> when we have one pending delivery agent connection, if one queue have two
> todo tasks, the related transport will be selected, but if one queue just
> have one todo tasks, the related transport won't be selected.
I repeat. The code is correct as it stands. More messages queued
to be delivered yield more opportunities to schedule a delivery.
Nothing weird here at all. In particular, with a delivery agent
connection pending, the single "todo" entry is going to be used by
*that* delivery agent when the connection completes, so no additional
agents are scheduled until that happens or more entries become
available.
Otherwise, under light load we'd wake up two delivery agents for
every entry, only to find that the second delivery agent has nothing
to do.
I'm going to stop the discussion here. You'll need to figure out
why the code is correct without additional input.
--
Viktor.
