max-cache-size query

[Doug Barton]

On 06/02/10 01:31, Techi wrote:
> but, my question is still not answered.
> Why on earth such huge defference in the number of connections on the firewall
> with the max-cache-size on and off? I still don't get it.

Imagine the cache as a bucket. With a large bucket the chances of the 
answer that any given client needs being in the bucket already are 
higher, which means they can connect, get their answer, and disconnect 
quickly, without the resolver having to make any additional connections 
to the outside world.

With a small bucket if the answer the client needs isn't there already 
it has to wait while the resolver makes anywhere from 1-4 _additional_ 
connections to the outside world before it can finally get its answer 
and go away. I'm seriously twisting things here to make a good story, 
but hopefully it gives you more of an idea of what is happening.

When it comes to the size of the cache on a name server you should set 
it to about 80% of the available ram on the system. If that turns out 
not to be enough, add more ram, or get a bigger system.


hth,

Doug

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