[Dovecot] dovecot scaling issue?

[Timo Sirainen]

On Wed, 2007-05-30 at 15:33 +0000, it-dovecot at ml.epigenomics.com wrote:
> Hi!
> 
> We are running dovecot-imapd on Debian sarge out of the backports.org
> packages (version 1.0.rc15-1~bpo1).
> 
> We have ~ 80 clients using secure IMAP.
> 
> I understand that imap-login has to run for every SSL connection. Thus I
> already increased the max value for the number of imap-login processes.
> 
> But unfortunately dovecot is unresponsive from time to time. Where can
> I tune the installation? Do I need to upgrade to 1.0.0, for which no
> backported packages exist for Debian sarge?

The most important thing to find out first is what exactly "is
unresponsive" means. Is it just slightly slower, or does it hang for
longer periods? Is the CPU being used 100%? Is load average high?

> auth default:
>   verbose: yes
>   passdb:
>     driver: passwd
>   userdb:
>     driver: passwd

Are the users in /etc/passwd, or are you using LDAP or something as the
backend?

If you try logging in, where does it feel unresponsive:

1. openssl s_client -connect localhost:993
 - Does it give "* OK Dovecot ready" immediately? If not, this is
login-process related.
2. 1 login username password
 - Does it give "OK Logged in" immediately? If not, this is
authentication related.
3. <enter>
 - Does it give an error message immediately? If not, it's probably
hanging in NFS chdir(home_dir).
4. 2 select inbox
 - Does it reply immediately? If not, it's probably hanging while trying
to read the mailbox via NFS.

Your login process related settings look fine, although if it's really
the problem you could try also login_process_per_connection=no.
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