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Re: [libvirt-users] Performance tuning questions for mail server



Hi,

>> Load on the server is regularly above 20, yet the processors
>> generally are idle and the host is still responsive.
>
> That's completely normal for an email server running spamassassin,
> in my experience, and has nothing to do with libvirt.  IME, the
> issue is DNS lookups, which spamassassin and the RBLs it uses make
> *heavy* use of.  Run a caching DNS on localhost with fairly
> agressive caching (i.e. go ahead and have it ignore TTLs and keep
> everything for at least 5 minutes) and I expect that you'll find
> that problem being rapidly resolved.

Thanks for your help, but as much as I'd like it to be a simple DNS
issue, I really don't think that's the case. I have a caching
nameserver running, and while there sure is a lot of DNS traffic, it's
got to be more than that.

This mail server does manage a lot of mail per day, but not enough to
even consume the 8GB I've allocated, and the "mailq" command typically
takes a few seconds to respond, even when there's only a few messages
in the queue.

iotop may report as much as 2M/s on the host, with an average of about
400-600K/s. Does that seem like a lot? I can write like 80MB/s at
least using dd to test.

My configuration does not use any of the optional CPU or memory
parameters from libvirt, so I'm pretty sure there is something more
that can be done to improve performance, but I just don't know how.

Thanks for any ideas.
Alex


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