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Subject: Hash replacement schemes

Author: Scott Gasch

Date: 01:15:58 12/10/00


Hi,

What kind of hash replacement schemes are commonly used in chess programs?
Until now I've been using no replacement scheme but when I tried to implement
one it broke the hash.  What I tried was a dirty count on each entry that was
incremented between moves... I would only replace over a hash entry if it was
dirty (from last move or earlier) or the depth of the replacement was >= the
depth of the replaced node.

I guess this breaks because you get the hash full of nodes with very large draft
and don't replace them to deal with low draft but important nodes.  Someone told
me about a 2 table system where you have an always replace and a good table...
thought being to save high draft "valuable" hash entries in the good table and
also save low depth but recently hit entries in the always replace table.

What are the other schemes people are using?  How bad is it to have no
replacement scheme at all (clobber everything)?

Thanks,
Scott



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