[Dovecot] Dovecot extremely slow!

Stan Hoeppner stan at hardwarefreak.com
Thu Sep 26 12:03:04 EEST 2013

On 9/25/2013 5:05 PM, Patricio Rojo wrote:
> Please help,
> Dovecot is running extremely slow for the last couple of weeks and it
> seems to be getting worse (or my patience running short).

Progressive degradation of mail server performance, whether an IMAP
mailbox server, or an MTA, is almost always caused by the storage
subsystem, usually due to filesystem free space fragmentation.

If you have a parity RAID array, have lost a disk and are running in
degraded mode, this can also cause large IO latency, slowing Dovecot.

Another common cause is heavy swap usage.  If you have a runaway process
or one with a memory leak, this will eat up physical RAM, causing heavy
swap usage.  If swap resides on the same spindles as your mailboxes,
this will degrade Dovecot performance.

If your box is hosted at a colo facility, or is in fact a VPS, it's
always possible a network problem or a clogged shared segment at the
provider is causing packet loss, which can also cause the client delay
behavior you have described.  If this server resides behind consumer
ADSL there could be a problem with your DSL provider's network.

In other words, if you didn't change the Dovecot configuration on the
day the performance first dropped, or very shortly before, then the
performance problem has nothing to do with Dovecot.  And this is almost
always the case with performance degradation.  The source of the problem
lie outside Dovecot, again, usually in the storage stack.  Start your
troubleshooting there.


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