[Dovecot] Dovecot very slow on a mailbox with > 700 IMAP Folders

[Steve Thompson]

On Thu, 5 May 2011, Timo Sirainen wrote:

> 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.

Interesting. I just converted a system from Courier IMAP to Dovecot, and 
found a massive performance increase. My own personal account has 655 
subscribed folders containing about 1.3 million messages. An LSUB "" "*" 
command takes of the order of about 0.1 second (the IMAP server has SATA 
disks and an Xeon E5345's at 2.33 GHz). Using alpine as client, a full 
scan of all messages to find unread messages (";puz") takes about 10 
seconds - with Courier, this takes over a minute. I don't know of a way to 
do the same test in tbird.

Steve