[imp] Scalability of IMP

[Peter Arien]

Joost De Cock wrote:
> www.kuleuven.ac.be
> webmail.kuleuven.ac.be
> 
> it's a university, so they should have a fair amount of users....

Here's the answer I sent to Oliver Kuhl:

-----------------------

To give you a rough idea: in 7 days we had 67262 logins
(9964 different users). That means approx. 600 logins per hour.

Of course that doesn't tell us anything about how those users
really use the system.

We're running IMP on one machine (dual pentium III with 800MB RAM).
Nothing fancy (no SCSI, IMP doesn't do much disk IO). That server
rarely drops below 50% idle time.

Performance is very dependant on the mail backend. Our mail backend
is a distributed system, whith DNS-based load balancing.

If one webmail server wouldn't be enough anymore, we would go for
a distributed system where load would be distributed by a very
simple round-robin system. There would be one webmail-entry system,
and that would use a very simple PHP script to send the user to
one of the webmail servers. The webmail servers would all use the
same MySQL database server to store/retrieve preferences.

Direct connections to the webmail servers (eg people typing the URL
of one of the webmail servers in their browser) would be rewritten
back to the webmail-entry system. In other words: the only hits
allowed on the webmail servers would be those hits referred by
the webmail-entry system or by the webmail server itself.

Summary: give your webmail server enough memory and CPU, and
make sure your backend mailserver(s) can handle the IMAP load.

-----------------------

PS1: logins per hour is counted between 09h and midnight.
PS2: with this one webmail server I don't only serve
      our own central mailbackends, but 10 other mailservers
      scattered all over the university

Greetings

-- 
Peter

  K.U.Leuven - LUDIT             -=- Tel: +32 16 322219
  peter.arien@cc.kuleuven.ac.be  -=- http://pa.cc.kuleuven.ac.be