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Subject: Re: double hash tables

Author: Robert Hyatt

Date: 09:59:10 10/08/97

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On October 07, 1997 at 21:05:39, Komputer Korner wrote:

>On October 01, 1997 at 09:32:00, Chris Whittington wrote:
>>Can we assume from this that there are two versions of Crafty, one that
>>gets released, and one that doesn't ?

Sort of, I suppose.  The "double store" version is the one I release.
It is faster, and at the speeds we see on the PC, it is better.  *if*
you could search at 5M nodes per second (like on a T90 for example), or
*if* you were constrained to use some tiny hash table (256K bytes for
example) then the multiple store is better than the double store, but
not by any really huge amount.  Maybe 10%.  But with the PC's poor
memory bandwidth, the multiple store costs about 10% in overhead (or
more because it thrashes hell out of cache as well) which more than
offsets the gain.  So I release that which runs fastest and works best
on the machines everyone will use...

>So does this mean that having a 2nd hashing algorithm kicking in when
>the hash table gets overloaded is the optimum for now?

I don't know how to switch in mid-stream.  Nor do I really know how to
detect when this becomes a problem, as the table is continually getting
overwritten even in normal cases...

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