Mailscanner and server load

[Kevin Spicer]

On Thu, 2004-08-26 at 03:55, David J. Duffner - NWCWEB.com wrote:
>         #3 - DON'T PANIC on load averages.  We're using MRTG and MailScanner
> MRTG and they don't agree with load averages, so you're not seeing a
> realtime accurate report!
<snip>
>     But overall you're seeing
> an illusion, we finally got a grip on it as MailScanner MRTG samples
> at a different rate and is giving us a REAL average to work with on
> loads.

Just to explain that a little.  MailScanner-MRTG samples every five
minutes and uses the five minute average load - thats the second load
average figure given by top and w.  This is handy as it means it takes
the average over its reporting period so is less prone to being messed
up by brief spikes.  A word of caution - older MSMRTG's didn't work like
that (it used the one minute average - which tended to be misleading).

Upping the RAM to 1G is a good idea, depending on your message
throughput you may be able then to put the MailScanner work directory in
tmpfs - that gives a significant performance boost so long as you have
enough physical ram (if it causes it to start swapping thats a bad
thing).
You need to get a feel for whether your system is CPU bound or IO bound,
the above trick will really help with disk IO related issues, network IO
issues can be helped by running a caching nameserver on the box itself
(very easy, theres an rpm for caching-nameserver I think, then you just
point resolv.conf and 127.0.0.1).
A load average of 3 isn't necessarily a problem anyway, so long as mail
is flowing with acceptable latency and you can cope with spikes.  Given
that your machine was able to battle through the backlog that built up
during your upgrade (hence the 30 load av) I'd say its not too
concerning (I'd still add ram, do the tmpfs thing and run a
caching-nameserver though).

Kevin




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