Author: Dann Corbit
Date: 14:26:54 02/06/06
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On February 06, 2006 at 17:16:14, Joseph Ciarrochi wrote: >hi folks, > >I have to use an old pentium 3 447 mhz computer to run engine vesus engine >matches, because my good computer has to be used for actual work :(. > >I can only give the engines 32 mb of hash. If i play really long games, I >presume this hash table will fill up quickly. > >How much of a performance decriment might i expect if i play long time controls > with such a small hash (compared to if i had say, 512 hash). It is a diminishing return for larger and larger sizes (it looks a bit like y = log(x)). So in that respect, additional ram past 32 meg is not as important as the smaller increments to larger. But very long time control will cause more overwrites. This is not a serious problem and filling the hash table is not a serious problem. Most chess programs also stick a key into the hash table which consist of the part of the hash entry that did not fit into the index. E.g., if I have a 64 bit hash checksum, and I have a 24 bit hash address, then 40 bits would go into the hash checksum. Often it is shortended to 32 bits, but this is not a serious omission. What that means is that even when your hash table is "filled" it just means that you will get fewer successful lookups. So your hash table "shrinks" a bit in usefulness due to over-writing positions that would have been valuable. It would matter a lot more if we had superfast CPUs and superfast memory. If your memory ran at CPU register speed you could use stupendous sized hash tables and it would truly be a bottleneck to have smaller sizes. Memory is cheap, and so if you can upgrade your machine it is good to do it. If you run blitz matches it won't make a big difference in effectiveness. If you run 40/2hrs, I expect you will see a significant boost. If you want to do correspondence chess analysis, I think a very large hash table is extremely important.
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