Supporting large caches (> 4GB) in BIND?

Shumon Huque shuque at isc.upenn.edu
Mon Feb 15 21:35:33 UTC 2010


On Mon, Feb 15, 2010 at 06:47:45PM +0100, sthaug at nethelp.no wrote:
> > > Have you *measured* the hit rate of your current BIND resolvers
> > > with different cache sizes? How many queries per second are you
> > > trying to support?
> > 
> > We do about 3,000 queries/second typically. I haven't measured query
> > -rates vs cache sizes. We've had max-cache-size set to 3GB for a long
> > time, but the process never exceeded 2GB until recent crashes prompted 
> > recompilation as 64-bit.
> 
> We do around 5500 q/s at 85% cache hit rate with a CNS process of just
> under one Gigabyte. This is not BIND but the statistics might still be
> relevant. 

Thanks, good to know. Looking at a recent snapshot, and if I'm
interpreting the bind stats correctly, I'm getting a similar 
cache hit rate (87%).

> If you feel that more memory is a worthwhile use of resources then by
> all means go for it. Personally I wouldn't consider it until my hit
> rate dropped to significantly less than 70%. However, the hit rate is
> of course dependent on your customers and their query profile, and it
> is entirely possible that our two cases are significantly different
> (mine is from the perspective of a commercial ISP).

We have gobs of unused memory , so ..

I'm not sure how different our profile is (university vs commercial
ISP). But the research project which is querying a very diverse
set of names that may not be typically queried will probably affect
the cache hit rate.

--Shumon.



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