Author: Ed Trice
Date: 14:35:59 06/17/04
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> >Take a disk position, and transform it into an EGTB index. > >Take a disk head. Seek to a sector. Load some blocks into memory. Decompress >the blocks. Get the answer from the decompressed pages and return it. > >How many evaluations do you think you can perform in this much time? Hundreds >for sure, maybe thousands. > >It is a mistake to probe every possible position. For sure, it will make your >chess engine play much worse. > >If you have bitbase files loaded into ram, it is a good idea to inquire of them >on every position. But an EGTB probe for every possible probe will cost you 100 >Elo, at least. And the faster the CPU and the more time allocated for the >search, the bigger the penalty. Dan, I understand the mechanism of how this works. The checkers program I worked on with Gil Dodgen has a few trillion game-theoretical value positions, spanning something like 120 GB, and with a 2 GB buffer the performance hit is not too bad. Why? Most-recently-seen position buffering. With less than 2% of the dbs resident in RAM, I still get above 90% of the CPU at all times, and most likely 95% for the overall search. Does the EGTB schema function on the same principles? We (the checkers world) do not seek the index from the wide panorama of positions. We seek to a BLOCK which houses, typically, 4K or 8K worth of indexed entries. We convert the position into an idex. We do a b-search for the block. The block is further subdivided into markers (typically 64 subdivisions) so then we b-search to the subblock. Then, and only then, do we decompress for the position's value. Of course the databases for chess also contain distance-to-whatever (mate/conversion) but the RAM-resident checkers databases do not. I will pay more attention to the decompression code. I just cannot imagine that a program can play one heck of a game for 60 moves, then get down to R + 2p vs. R + 1p and toss away the draw even after completing a 17-ply search. Probing the R+p vs. R db would have prevented this.
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