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Subject: Re: Hash hit ratios

Author: Michael Henderson

Date: 17:31:12 09/29/04

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On September 29, 2004 at 19:15:58, Rick Bischoff wrote:

>Hello,
>
>I use an aging counter in my hash table, that is incremented after each "real
>game move"-- anyway, Do these stats look "normal" for you regarding hash hits,
>etc?
>
>A hash hit: keys match (thereby giving a good move to try)
>
>The rest of the scores below mean that there was a hash hit and that the stored
>depth >= current search depth:
>
>exact: stored age == age and flag == exact
>upper: flag = alpha with no referenece to age
>lower: flag = beta with no reference to age
>I did the whole invalidating exact aging scheme because my program kept on
>getting into "hash loops" in certain positions where it would keep on playing
>the same line over and over again, thereby converting a won game into a draw.

I have never heard of this behavior.  Are you talking about from iteration to
iteration?  I would like to see an example of this.  I assume you are not
talking about getting a hash hit at ply one?

>
>I replace always EXCEPT where the search has the same age and less than equal
>depth to the stored entry.
>
>***** 11201 ms elapsed 1247030 nodes 111332 nps.  181809 probes %13.6242 hits,
>%0.0440022 exact, %2.67203 lower, %1.0577 upper. nulltry=127769 nullsec=84970
>ext:(mate=63,check=29699,pawn=143)

Your numbers seem low. I can get 16-25% exact+lower+upper hash cutoffs in the
opening position.

Michael



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