mailing list archives
Re: DNS caches that support partitioning ?
From: Jimmy Hess <mysidia () gmail com>
Date: Sun, 19 Aug 2012 23:08:20 -0500
On 8/19/12, Mark Andrews <marka () isc org> wrote:
As for the original problem. LRU replacement will keep "hot" items in
the cache unless it is seriously undersized.
Well, that's the problem. Items that are not relatively "hot" will
be purged, even though they may be very popular RRs. Cache
efficiency is not defined as "keeping the hot items".
Efficient caching is defined as maximizing the hit percentage.
The DNS cache may have a load of DNSBL queries; so all the entries
will be cold. The problem in that case is not low utilization, it's
high utilization of queries that are useless to cache, because
those questions will only be asked once, because in LRU there's no
buffer maintaining an eviction history.
An example alternative strategy is, you have a Cache size of XX RR
buckets, and you keep a list of YY cache replacements (not
necessarily the entire RRs, just label and a 1-byte count of
evictions), and you have a cache policy of: pick the entry whose TTL
has expired OR that has the lowest eviction count, that is
least-recently used or
has the least number of queries, to replace,.