performance issue with UID SEARCH

[Ben Burke]

Hi,

I'm running dovecot 2.2.x and I'm having an issue where I see many
dovecot processes use all the available IO on a server. According to
iotop the worst offenders seem to be in this state (NOTE: I swapped in
phony username & IP info):

dovecot/imap [someusername 123.456.789.012 UID SEARCH]

The server in question is running with Maildirs on top of an XFS
filesystem. Is there anything I can do to optimize "UID SEARCH" or find
out why it's being a problem? I've read
https://wiki2.dovecot.org/PerformanceTuning and the linked pages.

By "being a problem" I mean iostat -xmt 1 /dev/diskdevice shows 100%
utilization for long periods and in some cases io service times are
taking many seconds... which causes thunderbird to timeout when doing
things like appending messages to user "Sent" mailboxes.

Any ideas?

Thanks,
Ben Burke