On Tue, Oct 29, 2013 at 05:01:05PM +0000, Jeremy Harris wrote:
> On 29/10/13 16:19, Osborne, Paul (paul.osborne@???) wrote:
> >I have checked through the manual for the version we are running 4.72
> >(Debian - squeeze) and cannot see an option like:
> >
> >smtp_queue_size_backoff
> >
> >Where Exim does not respond to SMTP if there are X no of mails in its own
> >queue waiting to be processed.
> >
> >Is there such an option, if so what is it? If there is not can I add it
> >as a feature request? :)
>
> RFEs can always be opened at http://bugs.exim.org/
> For your immediate needs, I'd suggest putting some custom stuff onto
> your smtp connect ACL, involving a ${run } expansion to evaluate
> the queue size.
With a cache of the count that is updated periodically, rather than
every time it is queried. Scanning the queue counting messages
can be I/O intensive. You don't want to do that on every incoming
SMTP request. You probably also want a high/low watermark strategy
so that once the count exceeds the high mark, the throttling
continues until it drops below the low mark.
Such back-pressure tuning can be tricky. The queue can be large
in steady state with deferred mail to a destination that is down,
while other destinations are just fine, and you may not want to
stop accepting mail generally. When all mail is queued for the
same resource (e.g. waiting to be scanned), that's a more easy case
to deal with.
--
Viktor.
