Author: Mark Young
Date: 12:08:52 05/31/98
Go up one level in this thread
On May 31, 1998 at 12:43:39, Robert Hyatt wrote:
>On May 31, 1998 at 03:32:56, Don Dailey wrote:
>
>>On May 30, 1998 at 09:56:25, Robert Hyatt wrote:
>>
>>>On May 30, 1998 at 02:28:02, Steven Juchnowski wrote:
>>>
>>>>How much does hash table size effect performance?
>>>>
>>>>On one hand we hear that Fritz5 can gain about 40 ELO points by
>>>>increasing the hash size from 44MB to 100MB.
>>>>
>>>>On the other hand there are claims that doubling the hash size will
>>>>only improve performance by a few ELO points.
>>>>
>>>>I assume the above claims are based on tournament time controls.
>>>>
>>>>So which is the real picture, or is it perhaps that the sensitivity of
>>>>hash
>>>>size on performance varies from program to program.
>>>>
>>>>Regards
>>>
>>>
>>>there are at least a couple of things that could make Fritz far more
>>>sensitive to hash table size than other programs:
>>>
>>>(1) a poor replacement strategy. If this is true, then a larger table
>>>reduces replacement, which would produce better performance.
>>>
>>>(2) using the table for other things besides the normal score/best move/
>>>etc. If this is true, replacing *any* entry could be bad, depending on
>>>what is stored in the table.
>>>
>>>no one knows what Fritz does, but one of the above reasons is almost
>>>certain to be correct. I'd suspect (2) myself, since replacement
>>>strategies are well-known now.
>>
>>Is Fritz actually more sensitive to hash table size, or does it just
>>need bigger hash tables than the other programs? My impression
>>was that it probably hashed into quies and was so fast it needed
>>bigger tables than most others.
>>
>>If Crafty was 100X faster (on the same hardware), would you consider
>>your program more "sensitive" to hash table size than the others?
>>
>>My opinion is that Fritz's speed just makes it need more memory.
>>
>>I have a hard time believing reason 2 is likely. I agree with you
>>that reason 1 is also unlikely. My opinion is that Fritz's speed
>>just makes it need more memory and this makes it appear to be
>>"sensitive" to hash table size.
>>
>>If you were fed 200 calories a day, people might think you were
>>calorie sensitive. He seems to perform much better with just
>>an extra 200 calories added to his diet!
>>
>>Let me think some more about your second suggestion as a possibility.
>>
>>- Don
>
>
>I don;t think it is an "overflow" issue. IE I ran a few tests last year
>with Cray Blitz on a T90, searching about 5M nodes per second... and
>the
>variability I saw was about 30% from way too small to way too big. So
>bigger was better, but not a lot better. I suspect they store other
>things
>(ala hsu's "sticky transposition table" only more-so) that costs them
>dearly to compute when they don't find it in the hash... but that's
>only
>a "SWAG"...
Could you or Don explain what "sticky transposition table" are.
Thanks
Mark
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