From: Leandro Santi (lesantiuolsinectis.com.ar)
Date: Fri Jun 13 2003 - 10:48:38 CDT

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On Fri, Jun 13, 2003, Wietse Venema wrote:
> Leandro Santi:
> >
> > Well, I've been running the proxymap for a few days, and it seems that one
> > of its instances is getting most part of the work:
> >
> > % ps -f -p "`pgrep proxymap`"
> > UID PID PPID C STIME TTY TIME CMD
> > postfix 21272 12361 1 08:55:33 ? 2:04 proxymap -t unix -u
> > postfix 151 12361 1 07:20:31 ? 3:22 proxymap -t unix -u
> > postfix 16736 12361 1 12:15:12 ? 29:03 proxymap -t unix -u

Actually, the last proxymap instance has now 1 day of existance (that ps
snapshot was taken about 12:10 :-). So, the real numbers are:

first proxymap : ~ 1.07 % CPU
second proxymap: ~ 1.16 % CPU
third proxymap : ~ 2.02 % CPU

So it seems that the work is in fact being spread evenly (because the
first two are born at about the same time and have comparable cpu usage
rates, but the last one can't be compared against the other two because
it has had lived much longer hence has been working at rush hour).

> > I already understood that, when lots of work requests arrive, the Postfix
> > daemons will "naturally" discover and connect to the less active ones,
> > because of its (ingenious) design. However, I think that its a desirable
> > feature (second of third order if you like :) to spread the load evenly not
> > just when the whole (ie Postfix + backend) system is somewhat near saturation
> > but when working at cruise speed, too.
>
> The genius here was letting the OS scheduler do the work for Postfix
> (instead of fighting against it).
>
> What you see is that one proxymap process is sufficient most of
> the time. The other ones kick in when that process gets busy.
>
> Note also that trivial-rewrite will keep an almost persistent
> connection. If you like, shorten ipc_idle to a few seconds and see
> what happens.

Thanks,
Leandro

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