Viktor Dukhovni:
> On Wed, Jun 24, 2020 at 04:43:55PM -0400, Wietse Venema wrote:
>
> > For a given transport and destination, if all three classes have
> > work then round-robin interleaving gives each class gets 1/3 of the
> > delivery slots, 1/2 if there are only two classes with work, all
> > slots if there is only one class witth work, and zero if there is
> > no work.
> >
> > If implemented in oqmgr, it's brain-dead round-robin with FIFO.
> > What could possibly go wrong? :-) Well it does not interleave
> > deliveries within the same class. But, with single-recipient messages,
> > that wasn't happening anyway, so we are not making things worse.
>
> My instinct is that just "oqmgr" + coarse classes is not quite enough.
> There can be multiple large messages in one of the larger classes that
> can take a while to drain to a popular destination. There should
> still be some sort of preemption after a particular message group
> has consumed enough resources.
Possible solutions:
a) Within a class and destination, select round-robin by sender
key, and then deliver that sender's requests in FIFO order. That
would maximize fairness, while making the data more complex.
b) Within a class and destination, forget about FIFO order and use
random selection. That would not increase data struture complexity,
but the increased tail latency would weaken fairness.
c) Within a class and destination, shuffle the FIFO in a more careful
manner, or select randomly only from the first N entries in a FIFO.
Ideally, deliveries from different senders always interleave, and
no sender can hog resources.
Wietse
