dovecot - May 2007 - dovecot scaling issue?

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?

This is the output of dovecot -n:

log_timestamp: %Y-%m-%d %H:%M:%S 
listen: *:143
ssl_listen: *:993
ssl_cert_file: /etc/courier/imapd.pem
ssl_key_file: /etc/courier/imapd.pem
disable_plaintext_auth: no
login_dir: /var/run/dovecot/login
login_executable: /usr/lib/dovecot/imap-login
login_processes_count: 12
login_max_processes_count: 512
verbose_proctitle: yes
mail_location:
maildir:~/.Maildir:INDEX=/var/cache/dovecot/INBOX.%u:CONTROL=/var/cache/dovecot/INBOX.%u
mail_full_filesystem_access: yes
maildir_stat_dirs: yes
maildir_copy_with_hardlinks: yes
namespace:
  type: private
  separator: .
  prefix: INBOX.
  inbox: yes
namespace:
  type: public
  separator: .
  prefix: shared.
  location:
maildir:~/.Maildir/shared:INDEX=/var/cache/dovecot/shared.%u:CONTROL=/var/cache/dovecot/shared.%u
auth default:
  verbose: yes
  passdb:
    driver: passwd
  userdb:
    driver: passwd

Homedirectories are on NFS, /var/cache/dovecot is a local filesystem.
Clients are mostly Thunderbird, where max connection to IMAP server is
set to 5.

Greetings
-- 
Robert Sander                     Senior Manager Information Systems
Epigenomics AG    Kleine Praesidentenstr. 1    10178 Berlin, Germany
phone:+49-30-24345-0                            fax:+49-30-24345-555
http://www.epigenomics.com             robert.sander at epigenomics.com

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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