Author: Ricardo Gibert
Date: 18:21:37 08/31/03
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On August 31, 2003 at 19:44:28, William Penn wrote: >The more hash I allocate, the slower the kN/s speed. Thus 4MB (the minimum) is >the fastest in my tests, typically about 450kN/s. If I increase that to say >256MB hash, the speed slows down to about 400kN/s. The more I increase hash, the >slower the kN/s speed. > >The kN/s speed peaks, then eventually starts to decrease. How long this takes >depends on the amount of hash. However in my tests, the long term speed >advantage of bigger hash never catches up with the long term speed obtained with >smaller hash. Thus I don't see any advantage whatsoever to using a hash table! >The opposite seems to be true!? > >I'm using the Shredder7 GUI, Shredder 7.04 UCI engine, AMD XP Athlon 2400+/640MB >RAM (608MB available). The GUI says the maximum I can allocate to hash is about >455MB, so I'm not near the limit. Of course I'm using fairly common practical >positions for these tests in Infinite Analysis mode, and the above indicated >results are typical. > >I get very similar results running Shreddermarks with different size hash. The >more hash, the lower the Shreddermark and corresponding kN/s. > >Now, will someone please refute this, or explain what I'm missing or >overlooking? Thanks! >WP Your results are quite predictable. In theory, with no hash table at all a program should be able to run fastest in terms of NPS, since the time spent looking up a position can be skipped altogether. BTW, in practice, many programs assume a hash table of a minimum size to avoid breaking the code so you may have difficulty verifying this for yourself. You're focusing on just one statistic i.e. NPS, while ignoring the impact that a hash table has with move ordering and pruning transpositions. Try measuring time to depth and see if you arrive at the same conclusions.
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