Awfully slow dovecot

[Joseph Tam]

Robin Helgelin writes:

> We?re using dovecot 1.0.7, which seems to be the latest version
> available on CentOS 5.

It wouldn't be a bad idea to update this if you can, even if you have to
compile it yourself.  You'll benefit from many bug fixes, one of which may solve
your problem.

> Downloading emails are dead slow.  Really small emails goes quickly,
> but normal emails and emails with attachments are so slow to download
> it?s almost ridiculous.  I?ve googled some and found that it could be
> related to quota, but I disabled the quota plugins on imap with no
> difference.

The problem with "slowness" is that it can result from just about anything.
I've seen reports of slowness caused by LDAP handups, filesystem and I/O
polling, client issues, network issues, firewall issues, anti-virus stuff,
resource starvation.  That's just the stuff I remember.

You'll need to dig further to reduce the scope of where it can be going
wrong.  I would suggest getting hints from

 	- process tracing
 	- network snooping
 	- logs

Test if it's a mail client issue by sampling more than one mail client
(or better yet, talk IMAP directly to the server via telnet or netcat and
download a large piece of Email).

If that provokes a problem, work your way back to the server and do the
same thing on the server itself (bypassing the network stack) and see if
the problem still persists.

Depending on what you find out, at least you'll know which side of
the fence you should be looking at.

(Also, asks yourself the obvious question: did you change anything before
dovecot performance went down the tubes?  New hardware?  Patches?)

Joseph Tam <jtam.home at gmail.com>