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Subject: Re: hash tables

Author: Bob Durrett

Date: 17:04:33 12/21/03

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On December 20, 2003 at 10:53:56, Jay Hysenbeg wrote:

>hi,
>i was wondering what happens when u use low hash for a long time control. to the
>point where the hash is normaly filled before the eng has made its move.
>thank you
>jay h.

Your use of the words "long time control" suggests that you may be thinking
about situations in which it is practical and desirable to use long time
controls.

Most humans, when playing in real time against the chess program, would not wish
to wait a "long time" for the program to select it's next move.  The use of very
long time controls in such games would be neither practical nor desirable.

On the other hand, automated analysis [I call this "overnight analysis"] would
not require the presence of the human and no human would have to "sit and wait."
 Very long analysis times could be set for automated analysis.  The engine could
do it's work while it's human user was doing something else, such as sleeping or
at work.

An interesting question is what happens to the contents of the hash table during
automated overnight post-mortem analysis of a game.  If the game contains many
errors on both sides [as is typical of an amateur blitz game], and if the
analysis is set to examine moves where the evaluation of the previous position
in the game differs from that of the position being examined by only a very
small amount, then the product of the "overnight analysis" can be considerable.

In this case, it seems to me that size of the hash table, and the way it is
used, are especially important.

Testing the effects of hash on fast games would not address the "long time
controls" question.

There seems to be a huge difference in the way hash tables are used in playing
games versus automated post-mortem analysis of games.  My impression is that
hash tables are much more important in the latter case.

Bob D.




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