[Dovecot] 45second delays on log in

[Ben Marsh]

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