Author: Edward Screven
Date: 00:55:53 03/04/98
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On March 03, 1998 at 20:18:34, Brian McKinley wrote: >I have seen more than one reference to clearing the transposition table. >Is this necessary, and if not, why is it a common practice? The only >benifit I can think of is a negligible increase in lookup speed until >the table fills up again. i never completely clear the transposition table. i always try to keep as much information as i can. i do distinguish between old and new entries, where new means from the current search, and old means from a previous search. (i use this information to evict old entries faster than new entries, since it's less likely that they will be relevant in the future.) maintaining the distinction is very cheap -- it doesn't require updating the transposition table per-move. instead, each entry includes a small half-move number field. when an entry is created or updated its half-move number field is set to the current game half-move number. if i see an entry with a non-current half-move number, then i know it's old. my program includes a simple notion of search goals, which are really just parameters to the tip evaluator. if these goals change, then the current scores in the transposition table obviously become invalid. but instead of simply erasing the entries, i replace the score information of the entry with (-inf,+inf), leaving the suggested move information intact. this is a win because the best move given the old goals is usually still a good move given the new goals. i don't know if clearing the transposition table every move is common or not, but, given the above, i can't think of any reason why i would ever want to do so. - edward screven
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