[Dovecot] IMAP "freezing" on OSX

[Ben Carter]

Hi,

  I've got a problem with dovecot on an Intel Mac OSX box. Basically, I 
was running an older verion (0.8.?, I think), and everything was fine. 
Then, when I upgraded to 1.0.0 via MacPorts, I found that periodically 
the system gets into a state where it simply stops dealing with IMAP 
requests.

  This tends to manifest itself as Thunderbird simply stalling, not 
fetching any new messages or folder contents. Sometimes quitting and 
restarting Thunderbird will help, but at other times the problem 
persists even afterwards. It seems to be linked to specific mailboxes 
(or messages?) - often one "problem folder" will reproduce the effect 
100% whilst operating on the rest of the mailbox is fine.

  The problem /seems/ to often start as a result of trying to move 
messages between folders. I'm not certain if that's a root cause, 
though, or simply a consequence of "opening" an affected folder to 
perform the move. I have a spam folder with a large number (>10000) of 
messages in it, and trying to file stuff in there is a relatively 
surefire way to generate the problem.

  Once it's happened once, it inevitably escalates - restarting the 
client helps a bit, as does restarting dovecot. However, the only way to 
"fix" it and restore full functionality seems to be to delete all of the 
index and dovecot* files from the mailbox and folders... it generally 
takes a day or so after that before things start to go wrong again.

  All of this seems to point to corruption of the index files in some 
way, but the log is universally unhelpful - there are no error messages 
of any kind showing up there. The actual dovecot instance doesn't appear 
to crash or even "hang" properly - you can still make inbound IMAP 
connections OK, it's just that they don't ever give a response to 
commands that touch the affected mailboxes.

  Sometimes, I end up with temporary files lying around in the folders 
in the mailbox - apparently mails which were in the process of being 
moved when the server "gave up". I'm not sure if this is actually part 
of the problem, though, or just a symptom.

My configuration (from dovecot -n) is:

# /opt/local/etc/dovecot/dovecot.conf
ssl_disable: yes
disable_plaintext_auth: no
login_dir: /opt/local/var/run/dovecot/login
login_executable: /opt/local/libexec/dovecot/imap-login
mail_location: maildir:~/Library/Mail/IMAP
auth default:
   passdb:
     driver: pam
     args: *
   userdb:
     driver: passwd

I'm running this on my personal machine, so there's only one user on the 
system, which I have set up using MailDir (on HFS). There's a fair bit 
of mail in many of my folders, but I doubt that's the problem as the 
previous version didn't seem to have any issues...

I'm doing mail delivery using postfix directly into the maildir folders. 
That doesn't seem to be affected at all by this, though - mail still 
arrives fine even when Dovecot is failing to serve the folder contents 
to IMAP clients... you just can't see it ^-^

Has anyone seen an effect like this? Or does anyone have any pointers as 
to what I could try to debug it?

Any suggestions would be very greatly appreciated!

  Thanks!
-- 
  Ben Carter - ben at gunk.demon.co.uk / ben at saillune.net (preferred)