Hello,
On Fri, 21 Apr 2017 10:43:47 +0200 d...@evilcigi.eu wrote:
> Hi everyone,
>
> I'm running dovecot with quite a lot of users and lots of active imap
> connections (like 20'000). I'm using different user IDs for users, so I
> need to have imap {service_count=1} - i.e. I have a lots of imap
> processes running.
>
We peaked out at 65k imap processes before upgrading to a version where
imap-hibernate more or less works, but we're using a common ID.
---
dovecot 119157 0.1 0.0 59364 52216 ? S Apr01 48:25
dovecot/imap-hibernate [15137 connections]
---
The service_count parameter in this context is not doing what you think it
does, I have it at 200 these days and that will allow imap (or pop3)
processes to be recycled (they are labeled with "idling" when waiting for a
new client), not having one imap process serve multiple clients.
---
mail 591307 0.0 0.0 29876 4712 ? S Apr20 0:00 dovecot/imap
[idling]
mail 735323 0.0 0.0 27396 4196 ? S 13:20 0:00 dovecot/pop3
[idling]
---
The advantage (for me at least) is that the dovecot master process doesn't
have to to spin up a new mail processes each time during logins.
Since this process is quite single-threaded, it becomes a bottleneck
eventually.
> 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).
>
Unless you're making a change that affects the dovecot master process,
restarting everything isn't needed and you should set
"shutdown_clients = no".
You could still kick users with "dovecot kick" at a leisurely pace, but
security problems with the mail processes are rare.
> 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. I'm aware of the shutdown_clients directive that
> could help, but I don't like it -
I've very much gotten to like it, once things got huge and busy.
> I do want the clients get disconnected
> on dovecot shutdown and also I want them to relogin in reasonably short
> time after reload.
>
> Is something like that possible with dovecot or does it make sense to
> implement that in the future versions?
>
Run a dovecot proxy (if you have single box with all these users on it,
Mr. Murphy would like a word with you) and set
"login_proxy_max_disconnect_delay" to something that suits you.
Christian
--
Christian Balzer Network/Systems Engineer
ch...@gol.com Global OnLine Japan/Rakuten Communications
http://www.gol.com/
