Local delivery seems to limit IMAP performance

Eric Luyten Eric.Luyten at vub.ac.be
Wed Apr 6 11:37:05 EDT 2011

On Wed, April 6, 2011 5:07 pm, Gary Mills wrote:
> We run cyrus-imapd-2.3.8 in a murder configuration with one front end
> and one back end server.  One thing I've noticed is that local message delivery
> has a pronounced effect on IMAP client performance.  We've had to limit the
> number of lmtpd processes to 64 on both servers to maintain an adequate level
> of IMAP performance.  At peak times, we will have over 6000 IMAP sessions and
> over 500 SMTP sessions on the front end.  The result is that local deliveries
> are often delayed during peak times.
> What it is about lmtpd that causes it to affect IMAP client
> performance so profoundly?  Can anything be done about this?
> When I have an IMAP session running with mutt, it displays one line
> for each message, and displays the contents quite quickly as I select each
> message.  However, I've noticed that when I get a new delivery (for which I
> get a separate notification), there's a long delay when I select the next
> message.  It must be rebuilding some indexes at that time, and fetching the
> new copies.  Is that correct?  What could we do to improve this procedure?

+1    (i.e. I'd also like to learn more about these aspects)

We have a single instance Cyrus server 2.3.16 and five (5) LMTPD's already
give us the maximum delivery performance.
We routinely deliver over 20k messages per hour, the record stands at 27k.
That's with between 3,000 and 4,000 open IMAP sessions and a few dozen POP
users at any given time.

mailboxes.db is Skiplist with 514,000 entries, on SSD

How many deliveries per hour are achieved by other large Cyrus installations ?

Eric Luyten, Computing Centre VUB/ULB.

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