Without FTS, dovecot needs to open *each* and *every* email when doing text searches, which is understandably rather slow process.

Aki

On 27.2.2019 10.43, Marc Roos wrote:

I am not sure if this any help. From what I understand of maildir it has lots of separate files, thus uid/gid lookups. Try running something like nscd, that will cache these lookups?

-----Original Message----- From: Aki Tuomi via dovecot [mailto:dovecot@dovecot.org] Sent: 27 February 2019 06:24 To: Ben Burke; Dovecot Mailing List Subject: Re: performance issue with UID SEARCH

On 27 February 2019 03:27 Ben Burke via dovecot < dovecot@dovecot.org> wrote:

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

Are you using FTS? If not, you should. See https://wiki.dovecot.org/Plugins/FTS

Aki Tuomi