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Re: DNS caches that support partitioning ?
From: Andrew Sullivan <asullivan () dyn com>
Date: Fri, 17 Aug 2012 17:12:11 -0400

On Fri, Aug 17, 2012 at 04:32:45PM -0400, valdis.kletnieks () vt edu wrote:

I think John's issue is that he's seeing those other queries *not* benefiting
from the caching because they get pushed out by DNSBL queries that will likely
not ever be used again.  You don't want your cached entry for www.google.com
to get pushed out by a lookup for a dialup line somewhere in Africa.

Oh, yes, I see.  You're right, I misread it.  But the proposed
solution still seems wrong to me.  If the entry for www.google.com
gets invalidated by a new cache candidate that is never going to get
used again, the cache is simply too small (or else it doesn't have
enough traffic, and you shouldn't have a cache there at all).

The cache needs to be big enough that it has a thrashy bit that is
getting changed all the time.  Those are the records that go into the
cache and then die without being queried again.  If the problem is
that there's some other record in there that might be queried again,
but that doesn't get queried often enough to keep it alive, then the
additional cost of the recursive lookup is just not that big a deal.  


Andrew Sullivan
Dyn Labs
asullivan () dyn com

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