[Dovecot] vsz_limit

[David Warden]

On Feb 8, 2012, at 3:58 AM, Héctor Moreno Blanco wrote:

-snip-

> service imap-login {
>  executable = /usr/local/dovecot/libexec/dovecot/imap-login
>  inet_listener imap {
>    address = *
>    port = 143
>  }
>  inet_listener imaps {
>    address = *
>    port = 993
>  }
>  process_limit = 2048
>  process_min_avail = 20
>  user = vmail
> }
> service imap {
>  executable = /usr/local/dovecot/libexec/dovecot/imap
>  process_limit = 2048
> }

- snip, again -

> 
> The problem is at the moment of maximum load of the system. We can see many imap sessions but there are also many imap-login processes, which is weird. Has it something to do with any parameter of our configuration? We think is something with the vsz_limit parameter. How can we tune it?

I'm not 100% sure but if this is the case but it looks like you setting process_limit and process_min_avail in the imap-login service block is putting dovecot in "High Security" mode. http://wiki2.dovecot.org/LoginProcess has good details on that. In short, I suspect your settings are creating a new imap-login process for each new IMAP connection. As I understand it, vsz_limit is more important when running in "High Performance" mode where you have just 1 imap-login process that handles all new IMAP connections. That process can grow quite large if you have a lot of simultaneous IMAP clients.

> 
> Thank you very much in advanced.
> 
> Kind regards.
> 
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> Héctor Moreno Blanco
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> Security and Infrastructures Division
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Hope this helps,
David Warden