[imp] IMP performance under load

[andrew morgan]

On Tue, 24 Apr 2001, Stephen Fischer wrote:

> I'm evaluating IMP, along with a couple other IMAP web mail clients, and have
> just talked to someone who was experiencing a very high load on the machine
> running the web server.  He said that they were seeing a sustained load of
> about 100 running IMP 2.2.4 on a dual-processor SGI 3200.
>
> I was wondering a couple things.  First, has anyone else had experience with
> SGI machines and has suggestions?  Second, has anyone seen this sort of load
> in a solaris environment, which is what we're going to be running here?  And
> third, I would like to see what sort of hardware you're using if you have a
> user environment that is at all close to ours:
>
>     ~40 000 users
>     expected 150-200 concurrent users, although that guess could be wildly
>         off since we only have POP usage stats at the moment.
>
> Any information would be of great assistance, particularly since it's hard to
> stress test a system like this without actually putting it in a production
> environment, and by that point it's a bit late to turn back.

I don't know anything about SGI, but it sounds like something is going way
wrong if your load is 100.

We have about 25,000 users, although that number is very approximate.  Who
knows how many of those actually *use* their account?  :)

We run IMP 2.2 on a dual 400MHz Sun E250 with 1GB of ram.  There are
usually around 75-100 connections.  Everything is SSL.  The load average
varies quite a bit, sometimes getting as high as 4 or 5 for short periods.
Even then, IMP seems quite speedy from the end user perspective (I use IMP
myself on a daily basis, so I know firsthand).

The only real trouble I've had is when one of the imap servers is down and
IMP users are trying to connect to it.  Things don't time out quickly
enough, and users often retry many times, so the number of running web
processes can climb pretty high.  When that happens, the load usually goes
through the roof until the web server connection limit is hit.  After a
while, the imap connections finally time out and things settle down.  If I
know the imap server is going to be down for an extended period, I'll take
it out of IMP and put a notice on the login page to that effect.

	Andy