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Subject: Re: Storing the PV in a search routine

Author: Bruce Moreland

Date: 10:05:56 06/12/98

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On June 12, 1998 at 01:21:27, Roberto Waldteufel wrote:

>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?

I know this is how some programs work, but I haven't tried it, since I
have been gathering the PV from day one.

I'd be concerned that I'd overwrite the table in cases where I have a
non-huge table and a non-small amount of time.

It would seem like I'd over-write the PV pretty consistently unless I
was very careful.

It doesn't take 5-10% overhead to record the PV, and I wonder how you
could have arrived at this figure.


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