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Subject: Re: Expected Hash Hit Rate

Author: Scott Gasch

Date: 09:54:53 09/17/04

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On September 16, 2004 at 22:40:35, Michael Henderson wrote:

>On September 16, 2004 at 22:14:36, Stuart Cracraft wrote:
>
>>I have two variables "ttprobes" and "ttmatches".
>>
>>When I attempt a hash table probe, I always
>>ttprobes++.
>>
>>In the probe routine, if I get a match on the 64-bit
>>hash key, I do ttmatches++.
>>
>>My question is, for a tier-1 replace always table in
>>a standard null move R=2 searcher with material-only/pc-sq-only
>>evaluation, what kind of hit rate percentage should I expect with the
>>following calculation
>>
>>  ttmatches*100/ttprobes
>>
>>Is there some other hash-table-related statistic calculation I
>>should be doing to see whether the hash table is contributing
>>its fair share to the search.
>>
>>Thanks,
>>
>>Stuart
>
>Usually it's around 20-30% in standard time control searches. 15-20% for hash
>cutoffs.  I'm not sure about hash matching in 1 second searches but I would
>think it's relatively high because there is not much overwriting.
>
>Michael

I'd say I usually see 30-40+% "matched the signature" and maybe 5%-10% "got a
cutoff" on my hash table.  I use a 4 probe complicated replacing scheme for
storage.

I just ran the initial position to depth 10 and got 32.4% matched the sig and
only 5.5% got a cutoff for the hash.

In a hash-friendly position it can be higher... for example I just ran Fine #70
to depth 30 and got 84.9% matched the sig and 48.1% cutoff rate.

Scott



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