dovecot - Jan 2008 - Is there a way to limit multiple POP3 connections?

Hi all,

Please correct me if I'm going about this the wrong way.

We currently have a 3 system Mail server set up - two machines are the load
balanced frontends running Dovecot and Postfix, and the third machine is
our NFS.  Over the past 4 months or so, I've tweaked and optimized our mail
servers, and we receive roughly 3 million emails a day combined through
this setup.  

Sometimes, the IO Wait is horrible on the load balanced servers - it can
get up into the 80-90% range sometimes - it's usually when a lot of email
is being passed, or there are a lot of POP3 and IMAP connections.

One item which I believe to be hurting I/O performance is the fact I used a
RAID 10 setup using SATA II drives on an LSI Logic SATA I controller, in 32
bit mode.  Until we rebuild our mail setup (which may be another year down
the road), I want to make sure these servers are optimized to the fullest
just in case we get heavy I/O usage, it doesn't slow down if at all
possible.

One thing I noticed is that when issuing a 'ps aux | grep -i pop' or
'ps
aux | grep -i imap' I see the same username 2,3,4,5 times, sometimes more. 
When issuing a 'tail -f /var/log/dovecot.log' I notice that some users
log
into POP3 every 3 seconds, sometimes sooner.

Without upsetting the customer, is there anything I can do on my end to
disallow people logging into POP3 multiple times at once?  

Any tips on this is very much appreciated.  Thanks in advance.

Patrick

On Jan 9, 2008 5:58 PM, patrickm <patrickm at garlic.com>
wrote:
>
> Any tips on this is very much appreciated.  Thanks in advance.
>
This is pretty easy to achieve with imap, some clients fork off a
separate session. You can see this when you use a client, enter a
folder then enter another folder before the first one is finished with
its headers and so on.

If from your workstation you "while true; do fetchmail --silent
--keep; done" (or similar) and just grind a single mailbox with a
single process does it sooner than later "stall" if you run two or
more does it?

I have "crash-tested" a few times maillooping the above over a few
servers and it takes a long while to get impact from dovecot,
especially if dovecot's lda is delivering the mail (and thus updating
the indexes to be used by the pop/imap requests)

Other people might be interested in auth mechanism, mail storage type
and index locations.


-- 
Gabriel Millerd

On Wed, 2008-01-09 at 15:58 -0800, patrickm wrote:
> We currently have a 3 system Mail server set up - two machines are the load
> balanced frontends running Dovecot and Postfix, and the third machine is
> our NFS.  Over the past 4 months or so, I've tweaked and optimized our
mail
> servers, and we receive roughly 3 million emails a day combined through
> this setup.  
> 
> Sometimes, the IO Wait is horrible on the load balanced servers - it can
> get up into the 80-90% range sometimes - it's usually when a lot of
email
> is being passed, or there are a lot of POP3 and IMAP connections.
I updated http://wiki.dovecot.org/POP3Server. See maildir performance
and session locking.

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Timo Sirainen a ?crit :
> I updated http://wiki.dovecot.org/POP3Server. See maildir performance
> and session locking.
	Why with mbox the performance is getting worse for users that don't 
keep mails on server ? Is it because dovecot does not delete the index 
entry when it delete a mail ? So index file is becoming huge ? Anyway if 
the index file is correctly indexed access time should still be very fast.
	And what about maildir format ?

-- 
Laurent PELLISSIER @ Ecole des Mines d'Al?s

On Thursday 10 January 2008 05:59:27 Timo Sirainen
wrote:
> I updated http://wiki.dovecot.org/POP3Server. See maildir performance
> and session locking.
so according to this for POP3-only setups and v1.1 it is better to disable 
index files completely? Are there any drawbacks of disabling index files for 
POP3-only setups?

Regards, Arvids