dovecot - May 2011 - Dovecot very slow on a mailbox with > 700 IMAP Folders

Hello,
I am using Dovecot 1.2.9 on a 32bit on Ubuntu 10.04.2 LTS.

We got one user who uses folders in an "exessive" way. He has got 704 
subscribed folders. That means about nearly 3000 folders on the 
filesystem. Since ~ a week the user couldn't work because of timeouts 
when connecting to Dovecot (IMAP). Thunderbird doesn't show any folders 
- timeout - the webmail System (Groupoffice) only presents the INBOX.

I did some debugging and found that a lsub "" "*" that is
used by
Thunderbird takes > 5 minutes. Thunderbird disconnects after ~1 Minute 
showing the timeout. I entered the command directly via port 
communication. So this is no clientside problem. But there is no error 
message or something else in any logs.

I did some debugging with strace, too. It's about 22MB only for running 
the lsub command !? The Mailbox size is about ~2.2GB, so this should be 
no problem. The maximum subfolder level is about 13 - could this be a 
problem? You can find the structure (simply shown) attached.


Thanks for any help!!


Best regards
Ronny Becker


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Institut f?r Medizinische Diagnostik GmbH
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Telefon: 06132 781 249
Fax: 06132 781 9 249

ronny.becker at bioscientia.de
www.bioscientia.de

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On 5.5.2011, at 10.04, Becker, Ronny wrote:
> I did some debugging and found that a lsub "" "*" that
is used by Thunderbird takes > 5 minutes.
Something's very wrong. I just tested with 1000 folders in a subscriptions
file and it lists it in less than a second.
> I did some debugging with strace, too. It's about 22MB only for running
the lsub command !?
Run it with strace -tt and send me the output compressed?

Also dovecot -n output could be useful.

on 5/5/2011 1:04 AM Becker, Ronny spake the following:
> Hello,
> I am using Dovecot 1.2.9 on a 32bit on Ubuntu 10.04.2 LTS.
> 
> We got one user who uses folders in an "exessive" way. He has got
704
> subscribed folders. That means about nearly 3000 folders on the filesystem.
> Since ~ a week the user couldn't work because of timeouts when
connecting to
> Dovecot (IMAP). Thunderbird doesn't show any folders - timeout - the
webmail
> System (Groupoffice) only presents the INBOX.
> 
> I did some debugging and found that a lsub "" "*" that
is used by Thunderbird
> takes > 5 minutes. Thunderbird disconnects after ~1 Minute showing the
> timeout. I entered the command directly via port communication. So this is
no
> clientside problem. But there is no error message or something else in any
logs.
> 
> I did some debugging with strace, too. It's about 22MB only for running
the
> lsub command !? The Mailbox size is about ~2.2GB, so this should be no
> problem. The maximum subfolder level is about 13 - could this be a problem?
> You can find the structure (simply shown) attached.
> 
> 
> Thanks for any help!!
> 
> 
> Best regards
> Ronny Becker
> 
> 
What is the underlying filesystem, and if its ext3, is dir_index set on?