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List:       djbdns
Subject:    RE: CPU utilization of dnscache (no logging)
From:       Matt Simerson <MSimerson () interland ! com>
Date:       2002-02-28 14:46:02
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That means that your dnscache is getting a LOT of queries. You can verify
this by briefly turning on logging and processing the logs. 

I have a mail server farm with about 30,000 accounts on it and one dnscache
process running on a quad xeon 550. It normally chews up about 5% of one CPU
on the quad with a 400MB cache. It sounds like your mail server is keeping
it pretty busy. In such a case, there's a good change your pitching
non-expired records out of your cache because your cache is too small.
There's two ways to verify this. Once is outlined on Dan's web site, the
other is to turn on BIND, let it run for a few hours and see how much RAM
it's using. 

That last approach is to simply assume your cache is too small and try
giving dnscache another 50MB of RAM, restarting it, wait an hour (for the
cache to fill) and see what your load looks like. It'll probably drop a bit.
Then, follow the dnscache instructions for tuning your cache size and you'll
be all set. I wrote an articles on this topic:
http://matt.simerson.net/computing/dns/dnscache-article.shtml.

Matt

> ----------
> From: 	Yusuf Goolamabbas
> Sent: 	Thursday, February 28, 2002 5:29 AM
> To: 	dns@list.cr.yp.to
> Subject: 	CPU utilization of dnscache (no logging)
> 
> Hi, I have a fairly loaded MTA box with a local dnscache of 10MB.
> The box is a dual-PIII 750 running FreeBSD 4.4-stable and I have
> disabled logging 
> 
> I have observed via top that dnscache generally takes about 10% CPU and
> is pegged there whilst looking at a continuous output from 'top',
> amongst the processes on the box, dnscache seems to take the maximum
> amount of CPU
> 
> I am not sure if this is a bad thing. If it is, what would be the likely
> cause and what can I do to alleviate this
> 
> Regards, Yusuf
> -- 
> Yusuf Goolamabbas
> yusufg@outblaze.com
> 
> 
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