Re: Qmail on lists.debian.org is costing me real money
On Mon, 16 Mar 1998, Mark Baker wrote:
> > have raised the limits to allow 240 concurrant remote deliveries. Any
> > mailer which cannot handle >100 concurrante remote deliveries
>
> As far as I know exim can (the documentation doesn't mention an upper limit
> on the number of parallel deliveries), though it isn't necessary the best
> thing to do, as the overheads of forking more processes to do the deliveries
> can take out a lot of the potential speed gain, particularly when delivering
> to well-connected hosts.
This is especially true for mailers like exim and sendmail that have a
high per-process start up and a slow 'IPC' system. Qmail forks and
distributes -VERY- quickly so you do get excellent scalability.
> > or cannot handle that sort of message volume is simply not acceptable.
>
> Qmail probably can handle a higher volume than exim, but the volume you're
> getting isn't close to the limits of either, or even of sendmail.
I am not terribly concerned with volume per-say, but peak thoughput -
specificaly total time to delivery of ~90% of the emails. Qmail gets ~1
min, that's a sustained rate of 7msg/sec and it hits a load of about .6 on
the PPro. I imagine exim and even sendmail can manage to deliver the 200k
emails, but will they do so well on thoughput?
There is another aspect to having a high concurrancy level, that is that
over 40 hosts on the lists are slow, if I were to set qmail to 20 then
those 40 hosts would hit and everything stops for about 4 mins while they
timeout. That is wholly unacceptable. At any time I find that about 20-40
of the available outgoing processes are connected to such slow hosts.
Jason
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