[Dovecot] Dovecot 1.0-stable mbox performance and disconnections

[Chris Wakelin]

I've got some of our busiest users now using Dovecot instead of UW-IMAP 
with mbox-format mailboxes and predominantly Outlook Express as the client.

Doing some perfomance monitoring (with Solaris 8 process accounting), it 
looks like Dovecot needing to read only 30-50% of the disk blocks needed 
by UW-IMAP, but I was hoping for better!

What seems to happen, is that most of the connections use only a small 
number of blocks (due to Dovecot indexes, presumably) but occassionally 
a process will read lots of blocks, sometimes even more than a UW-IMAP 
session.

Is this expected, or is something going wrong with the index updates? I 
have the default sync settings, I think (mbox_dirty_syncs = yes, 
mbox_very_dirty_syncs = no, mbox_lazy_writes = yes)

My INBOX is an extreme example with ~10,000 messages and most processes 
reading a few hundred blocks but a couple using 20,000 or so!

Also, Dovecot seems to be dropping connections, sometimes, for no good 
reason (putting some extra i_info lines suggests for "inactivity"). 
Thunderbird tends to reconnect automatically, though. It seems it may be 
happening at the end of an IDLE command, something like:-

4 IDLE
+ idling
* 1005 EXISTS
DONE
* 1005 EXPUNGE

but then the expected

4 OK Idle completed

never comes.

Has anybody else seen this?

Best Wishes,
Chris

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Christopher Wakelin,                           c.d.wakelin at reading.ac.uk
IT Services Centre, The University of Reading,  Tel: +44 (0)118 378 8439
Whiteknights, Reading, RG6 2AF, UK              Fax: +44 (0)118 975 3094