Re: [exim] Setting for extra exim processes

Peter Bowyer wrote:
> On 23 April 2010 08:34, Mark Thornton <mthornton@???> wrote:
>> On 23/04/2010 08:08, Peter Bowyer wrote:
>>> On 22 April 2010 23:30, Marc Perkel<marc@???> wrote:
>>>
>>>> I'm sure it's in the docs somewhere but I can't find it. What is the
>>>> setting to allocate extra exim processes to listed for incoming
>>>> connections. I'm looking to allocate spare processes to increase
>>>> performance.
>>>>
>>>> Thanks in advance
>>>>
>>> There isn't one - Exim has one listener that forks a new process for
>>> each connection. SMTP doesn't have the real-time demands that (eg)
>>> HTTP has, so doesn't need the kind of architecture that an HTTP server
>>> has.
>>>
>>> Peter
>>>
>>>
>>>
>> Clients MUA deliver mail using SMTP and incur a delay, sometimes with an
>> irritating dialog box, if the SMTP server is slow.
>
> Indeed, but the tolerable delay is at least an order of magnitude
> greater than for an HTTP request. And there's exactly one connection
> per batch of emails sent, compared with potentially many per web page
> request. The engineering problem is completely different.
>
> Peter

.. including the reality that even a bog-standard Exim under heavy-enough load
can exhaust the I/O resources of fast RAID arrays on most OS and hardware LONG
before it hits the wall on how fast it can spawn child processes.

Ergo, if/as/when there seems to be a need for speed, something other-than
spawn-rate will need money thrown at it first.

CAVEAT: Personally, I'd run out of PostgreSQL connections long before that, so
it may look as if it is Exim that needed tweaked but would be found not really
so on inspection of the logs.

Bill