Performance Enhancements

[Scott Adkins]

Okay, since we turned on MailScanner with Spam Assassin and Sophos, we
have definitely seen high load come out of the server... It looks like
the culprit is Spam Assassin.  SA seems to take about 5 times as much
CPU to process mail as what Sophos does (which is backwards from what
I was expecting, actually).

The system we are running this on is a pretty decent system.   It is a
two member Compaq Alpha Tru64 5.1a cluster.  One member is an ES40 with
4 EV6.7 667Mhz CPU's, 4GB CPU cache and 8GB memory.  The other member
is an Alpha 4100 with 4 EV5.6 600Mhz CPU's, 4GB CPU cache and 6GB memory.
The first member is more than twice as powerful as the second member is.

This is our primary email system, and we regularly see 400-500k worth of
emails go through the system on a daily basis.  We support well over 60k
users and typically have 1500+ concurrent IMAP/POP users logged onto the
system.  The system performs great under these conditions...

The idea was to run MailScanner and mail queue processing on one machine,
and our Cyrus IMAP and IMSP servers, as well as everything else on the
other machine.  We still saw high loads coming from the MailScanner stuff.
In fact, MailScanner literally drover our second member into the ground
(poor thing).

I am interested in what other large sites have done to optimize the
processing of spam and virus scanning.  I currently run with 20 MailScanner
processes, since we have 4 CPU's.  From what I can tell, it pulls in 100
messages at a time to process in a large batch and then sends them on their
way.  Doing it this way shows that disk IO gets slammed, and when it does
recover, the CPU gets slammed, and then it starts all over again.  I am
thinking that maybe processing smaller chunks of emails might even out the
load a little and maybe make things run a bit better.

Another thought is with Spam Assassin.  I know it has the capability to run
in daemon mode (spamd).  Does MailScanner even support this?  Does running
spamd in daemon mode give you any performance advantage at all?

Anyways, I thought I would check to see what other people are doing...

Thanks!
Scott
-- 
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      Scott W. Adkins                http://www.cns.ohiou.edu/~sadkins/
   UNIX Systems Engineer                  mailto:adkinss at ohio.edu
        ICQ 7626282                 Work (740)593-9478 Fax (740)593-1944
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