Author: Robert Hyatt
Date: 10:05:43 09/26/01
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On September 26, 2001 at 05:34:56, Sune Fischer wrote: >On September 25, 2001 at 20:11:57, Robert Hyatt wrote: > >>>>That is correct. But the way zobrist works, it is far more likely that >>>>that position is a _real_ match rather than a false match... So that once >>>>you fill the table, you can't assume that _every_ probe from that point >>>>forward is a false match. very few will be in fact... >>> >>>Well no, see my other post: >>>http://www.icdchess.com/forums/1/message.shtml?190349 >>>You forget that the problem here is, that you would not >>>be able to update any entries, and so as the game evolves, new positions will >>>occur and old ones will never be re-seached. This will lead to collisions. >> >>You overlook that positions get overwritten _all_ the time in the search. This >>is a two-way street. They get overwritten. They get reused. They will, on >>occasion, get incorrectly reused (collisions). But once it is full, the table >>is not just "full". It will still get overwritten furiously because of all the >>shallow leaf searches that demand to store information in the table... > >Yes so true, but if your table is twice as big, then you have twice as many >entries to overwrite, the likelihood of you missing one that eventually ends up >as a collision is therefor greater. >And as you increase the size of the table, the average "age" of each hash >element will also increase and thus diminishing the chance of a good clean hit. > >>IE I don't believe that doubling the hash size will double that collision >>rate. But that I can test when I have some time. It will be interesting to >>try. I might get time on a machine with 16 gigs of RAM so I can try doubling >>several times to see what happens. > >Good idea, but you might want to use smaller keys, or you will have to let it >run forever to get a good statistic. > >Thank you for the clear answer BTW, we disagree then, no harm in that :) I really don't want to test with smaller keys. When I tried 32 bits in the tests Stanback, I and others did, it was horrible. Collisions per second. I didn't think the search could stand that. However, I have never tried to determine how many collisions (replace this with bogus scores) the search can tolerate with no ill side-effects. That would be a _very_ good paper. Which I suppose I will write if nobody else does...
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