[Dovecot] 45second delays on log in

Charles Bueche charles at bueche.ch
Tue Nov 14 14:31:03 UTC 2006


maybe a stupid idea, but it looks like a double DNS timeout. Can the server resolve the incoming IP addresses to names ?


Ben Marsh wrote:
> Dear List Members,
> We have been running Dovecot as an IMAP server for web based access to
> email for our customers.  At the moment, when the server is under load,
> some users are finding that it takes 45 seconds to log in.  I was
> wondering if any of you guys would have any tips.  I would love any
> information that would help solve or debug this issue.
> Background information:
> The server is Debian with kernel 2.4.31.  We are running Dovecot
> 1.0rc6.  I have reviewed the change logs and not found any changes
> pertinent to our situation from rc6 to rc14 (But maybe I am wrong).
> We have our own auth mechanism.  This auth mechanism is the same used
> across our other products and we haven't had the same delays with the
> other products.  From the information in the various log files the auth
> mechanism responds almost instantaneously but it still takes a long time
> for
> 1 OK Logged in.
> message to arrive on the screen when using telnet localhost 143 to login.
> All the mailboxes are stored over NFS. I have taken the step of moving
> the INDEXES from NFS to a local hard drive using
> default_mail_env = maildir:%h/mail:INDEX=/spare/%h
> in the config file.  (/spare is a locally attached hard drive).  We are
> using Maildir for our mailboxes so I am told that locking should not be
> a problem.  A mailbox would never be accessed by two machines
> simultaneously due to the architecture of the system.
> In order to gain performance increases we also implemented an  IMAP
> proxy between the webmail client and the imap server.  This removes
> delays in all but the first attempt to access webmail.
> When logging into a user for which login has been verified to take about
> 45seconds deletion of the large numbers of messages seemed to speed up
> login for that particular mailbox indicating to me that it was other
> things that dovecot does after login and before the 1 OK Logged in.
> message is displayed that takes up all the time.  Unfortunately this
> theory failed when I tried it with other users.
> I have also analysed the log files.  of the 100,000 lines in the log file
> 49 were messages:
> Child 12040 (login) returned error 89
> 54 were messages:
> imap-login: Master sent reply with unknown tag 18
> The actual number at the end of the message changes lots.
> The frequency of the extended logins would make it extremely unlikely
> that these messages are the problem.
> Any help is very much appreciated.
> Thanks,
> Ben Marsh

Charles Bueche <charles at bueche.ch>
sand, snow, wave, wind and net -surfer
A-Cat SUI 192

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