Author: Bruce Moreland
Date: 10:59:15 06/14/98
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On June 14, 1998 at 03:31:12, jonathan Baxter wrote: >I find the file probes to be pretty expensive---in KnightCap the disk >seeks >can cost up to 2/3 of the processing time. But I have two reasons for >doing this: speed is one and the other is if you can do it accurately >then you may be able to generalize to more pieces without having to >compute all positions. My endgame database format is probably quite similar to Steven's. I hear that he stores everything as one byte, I store my values using the number of bits necessary to store the largest value in the file. So some of my 4-man classes are quite a bit smaller, but most of the 5-man classes are about the same size, since you get some pretty big values. I bring up this point in order to discount the differences, effectively they are the same format. It has been my experience that on a modern machine with reasonable memory and a hash table that isn't crowding the machine, that you can do 4-man probes and still go pretty fast. The relevent tables end up in the disk cache, and they are 3-10 megabytes, so you can fit a few of them in memory at once. If you try to access the 5-man tables at the tips and in the tree, you will go dog slow. Mine would be hitting 300-500K nps without those tables (on my 533 mhz Alpha), but you start adding in tables you can get under 20K, no problem. There is a *big* difference between 4-man and 5-man tip probes. And I have a nice 9 gb SCSI disk, too, so it's not the disk. It is an open question whether the increased evaluation accuracy (and ability to accurately prune out some sub-trees) outweighs the bogging you get when you start to get close to a 5-man ending. I've never tried to figure it out for real, I'm just trying to keep my eyes open during games. I still use all the tables I can fit on that disk (I have 18 gb of them, so they don't all fit), but I think it hurts in some cases, like queen and a few pawns versus queen and a few pawns. This one especially seems to go slow, and I've drawn or lost some cases that I think should have been shifted a column in my favor. bruce
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