Computer Chess Club Archives




Subject: Re: Storing the PV in a search routine

Author: Roberto Waldteufel

Date: 22:21:27 06/11/98

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Do you think the PV is actually worth the overhead of gathering it,
bearing in mind that the information in the hash table, ie the killer
moves stored with each node, effectively allow the PV from the previous
iteration to be quickly retrieved in the current search? When I first
implemented PV in a standard alpha-beta search without hashing (it was
on a machine with hardly any RAM), I found a speed-up of about 40% by
following this line first. Later, when I had more RAM to play with, I
implemented a hash table, which speeded up the search a bit more.
However, with the hash table working, I found that the search didn't
need the PV list any more, because it almost always found it from the
table, and so now I only bother to return best move at the root node and
I find the search increases in speed by another 5-10% or so. Of course
there is the risk that a PV node may have been overwritten, but this
occurs too rarely to hurt performance as much as maintaining the PV
separately did, particularly if the hash table is large. Does anybody
else use the hash table rather than the PV in this way?


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