Author: Don Dailey
Date: 00:32:56 05/31/98
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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
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