Christof,

I read this several years ago as a "theory". I recollect that the author had good arguments to support the theory, but also had acknowledged that one couldn't at all be sure because this is a proprietary thing which has remained well guarded.

Has there been something since which confirms this, so that it is now reality as opposed to theory?

regards,

Jim N



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>The Rushmore engine creates a bitmap for any index expression. That's a memory block where each bit represents a record. When a bit is 1, the record is part of the selection, when it's 0, the record is not part of the selection. This bitmap is created based on the index tree. In order to perform logical operations like AND or OR, all VFP has to do is to use bit oriented CPU commands to combine two bitmaps into one. Since that's done on the CPU level, it's quite fast.
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>Such a bitmap can be re-used until the cache times out, by default about 300 ms. After that, VFP recreates the bitmap if necessary.
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snip