[Dovecot] Performance problems while running doveadm purge

[Jost Krieger]

I have a rather large and active mdbox (28 GB, 3M mess, 1200
deliveries/day). I usually have no problems working with those mails,
and there is some batch processing going on (via doveadm).

Every few weeks I try my luck running doveadm purge, and this
a) crunches about 5GB (to be expected),
b) takes rather long (ok),
c) leads to long stretches of blocked mdbox, which is the problem.

I always turn off the batch processing, but deliveries take so long that
they sometimes give up after timeout (they will come back later), and
the IMAP clients get blocked for long minutes. Sometimes even the purge
run aborts because of 3-minute-timeouts.

What could be going on here (2.1.10)?
 
Jost
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