Author: Robert Hyatt
Date: 15:15:57 12/13/01
Go up one level in this thread
On December 13, 2001 at 17:15:16, David Rasmussen wrote: >On December 13, 2001 at 06:07:37, Wylie Garvin wrote: > >>Hello, >> >> Does anyone know what the best-performing rehashing scheme is? I read >>somewhere (Heinz) that multiple probes in one table perform better than separate >>tables. I've also heard that subtree size is best for choosing a node to >>overwrite. What does the board think? >> >>wylie > >It has been "proved" that a two-level table with one table being depth >prioritized (I don't remember how many percent of the table that should be depth >prioritized, optimally). Crafty uses this approach, with 1/3 being DP, if I >remember correctly. I think it was in Brucker's thesis about hashing in game >trees. > >/David "proved" is too strong a word. multiple probes (2 or more) certainly reduce the size of the tree. But they also have a fixed cost associated with them (they consume memory bandwidth that is already scarce). 2-level is a compromise between (a) using more bandwidth and going slower and (b) doing only one probe which will make the tree a bit larger. Smaller trees are good, so long as the total search time is also smaller. If you spend _too_ much time reducing the size of the tree, the cost of reducing the tree size may well exceed the savings caused by searching a smaller space.
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