System load spike on dovecot reload

[Jochen Bern]

On 04/21/2017 10:43 AM, dave at evilcigi.eu wrote:
> Everything works fine, until I reload dovecot configuration. When that
> happen, every client is forced to relogin in the same time and that
> causes a huge system load spike (2-3000 5 min load).

A system load of 3000 means that an average of 3000 processes would like
a bit of CPU time, not that the system's unable to *provide* that to
them, if only the amount of CPU each needs is small enough. You want to
look at the actual percentage of CPU used (and at the total number of
processes, to see how close you might be to running out of PIDs).

> I was thinking that it would be great, if dovecot wouldn't kick all the
> users in the same time during reload, but somehow gradually, during
> specified interval.

That wouldn't help unless the kicked clients, which will likely try to
reconnect immediately, *can* reconnect at once; otherwise, at the end of
the grace period, you'ld still have 100% of the clients banging on the
doors to get back in simultaneously.

So "old" and "new" dovecot would need to run in parallel, with all the
incompatibilities and resource restrictions *that* might entail, seeing
that there's obviously *something* that changed and prompted you to try
and restart dovecot in the first place.

In other words, I don't think that the dovecot code *can* cover all
those cases on its own - providing two suitably separate environments
(like with Kevin's proxy+docker suggestion) is IMHO the way to go here.

Regards,
-- 
Jochen Bern
Systemingenieur

Fon:    +49 6151 9067-231
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