Viktor Dukhovni:
> On Wed, May 15, 2013 at 12:22:41PM +0200, Patrik Rak wrote:
>
> > >There is no "them". This is not an analysis.
> >
> > The "bad guys" was a metaphor for slow mail which consumes available
> > resources.
>
> The metaphor is flawed, you need a model that considers message
> rates entering the active queue from incoming and deferred. A
> queue whose output rate exceeds its input rate is nearly empty.
With all due respect, it seems to me that we all three have a handle
on a part of the problem, but none of us appears to be versed in
queuing theory.
What I recall is that queue lengths depend not only on AVERAGE
arrival rates. The variations in arrival rates make a huge difference,
as experienced daily with queues before ladies' bathrooms (yes I
am aware that ladies, unlike email, don't back off exponentially).
Short of adding extra concurrency nothing is going to clear a
persistent source of slow mail (or a sufficiently-large deferred
queue). However I this is not the scenario that I have in mind.
and I think the same holds for Patrik.
We just don't want to dedicate too many mail delivery resources to
the slowest messages. Faster messages (or an approximate proxy:
new mail) should be scheduled soon for delivery. It should not have
to wait at the end of the line.
Now we could take advantage of the fact that in many cases the
"slow" and "fast" messages cluster around different sites, thus
their recipients will end up in different in-memory queues. If
there was a feedback of fine-grained delivery agent latencies to
qmgr(8), then could rank nexthop destinations. Not to starve slow
mail, but only to ensure that slow mail does not starve new mail.
Wietse
