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Subject: Re: HashTable size question

Author: Dann Corbit

Date: 17:15:19 02/04/05

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On February 04, 2005 at 19:48:49, Thomas Mayer wrote:

>Hi Dann,
>
>>> Just wondered what what size HashTable you would use if your computer had
>>> 1GB ram on a Dual Xeon 3.2GHZ for a standard game of 45 15. Looking to
>>> maximize the strength of the computer. I have been working with 512MB,
>>> 256MB and 128MB. I find 512mb seems to work better.
>
>> At slower time control (e.g. 45'+15") huge hash is good, and the bigger the
>> better.
>> At faster time controls, it will do worse and worse.  If you play with 512
>> megs hash and play game in one minute, it will do very poorly
>
>well, this was true as long the engines delete the hash after each move...
>nowadays I am not that sure, I believe Bob Hyatt was correct with his statement
>that usually more is always better... Even in a 5 minutes game most engines
>might fill even 512 MB hash quite easy...
>Of course it is not easy to test that when we have in mind (I think this one is
>from Christophe Theron) that doubling hashtables is around 7 Elo... I think this
>number is quite near to the truth...
>
>Greets, Thomas
>
>P.S.: Of course it differs between the engines...

ChessMaster (for example) clears the hash every move.

I have seen huge hash perform horribly with fast paced games with several
programs (not necessarily knowing for sure why).

Another thing to watch is that really large hash can have problems when you load
other memory hogs (certain MS products spring to mind) and when you multitask
many programs, you might start using disk for RAM.

Best bet is to always measure and when you do your games, make sure that the
conditions are exactly the same as when you measured.



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