[Dovecot] POP3 vs. IMAP Load/Memory usage in Dovecot 1.0.15

[lists at truthisfreedom.org.uk]

Quoting Stan Hoeppner <stan at hardwarefreak.com>:

> On 7/11/2011 1:24 AM, Matthew Macdonald-Wallace wrote:
>> On Fri, 2011-07-08 at 10:48 +0100, lists at truthisfreedom.org.uk wrote:
>>> We have noticed that the IMAP servers appear to be under much less
>>> load and utilising drastically less RAM than the POP3 servers and I'm
>>> wondering if there is a reason for this as we have seen some swapping
>>> onto disk yet we are only handling 500 concurrent POP3 connections to
>>> each server at any given time compared with over 600 IMAP connections.
>>
>> Am I to take it that this is expected behaviour?
>>
>> If anyone can shed more light on this I'd be very grateful.
>
> More specific information would be helpful.  Load as shown through top
> doesn't really tell anything.  Are you simply seeing memory pressure?
> Is all that RAM being used for block device cache or actually eaten by
> the pop servers?

Hi Stan,

Thanks for getting back to me.

The Load average comparisons are taken from Munin graphs and based  
upon the servers being in production for five days between Monday and  
Friday.

The vast majority of the RAM usage is cache, however there is still a  
discrepancy between the IMAP servers and the POP3 servers.

I guess all I'm really after knowing is if there is a reason why this  
is the case so I can put my mind (and those of my team!) at ease  
before we start making other changes to the infrastructure - the last  
thing I want to do is increase the load on these nodes and watch them  
die because they didn't have enough resources.

Kind regards,

Matt