Ted Lemon wrote:
How deep do you expect the name tree to get? I rarely see anything
more than four levels deep, and three times through the loop isn't
a whole lot.
Er, if on average you have to do three hash lookups instead of one,
and hash lookups are the main expense to answering a query, then that
would be 66% performance reduction on average on _every_ query. That's
pretty significant. Am I missing something? Why does this sound like
"not a whole lot" to you?
i think if flattened hashing is an inefficient way to implement a dns
cache, then it should and will fall out of favour. in 2002 or so, for a
non-open-source project, we (vernon schryver and myself) implemented a
dns cache as a recursive hash table in the general style of bind4/bind8,
but with strong module boundaries, and arrays for sparse child-sets that
morphed into variable sized hash tables when density increased. this is
where resimprove-00's nxdomain treatment was first implemented, and it
worked well, and it the whole thing was extremely fast, as well as
memory efficient.
so whenever i hear words like "that'll be slow for flat-hash dns caches"
it reminds me of the joke that begins "doctor, it hurts when i do $this"
and ends with "well, then don't do $this".
--
P Vixie
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