I don't need to test to know that the database solution will be slower than the hash solution as long as the hash fits in conventional memory, and I think you know the answer to that too. But at some point, 300_000 k/v pairs, 500_000, or maybe a million, the hash is going to cease to be a plausable option due to memory constraints. Given that the OP is asking about trying to get tandem lookup hashes to occupy the same memory space is a pretty good indication that (s)he is running into memory problems.

One avenue that folks often take when they find that they just can't hold the whole dataset in memory is to turn to databases. Them's the breaks. Tough decisions will have to be made. Either live with the inefficiency of not having the tandem lookup hash capability, or live with the inefficiency of the overhead of a database.

If holding the dataset in memory once is ok, but twice is impossible, then you can't have a tandem pair of lookup hashes.

If memory isn't an issue, then the original question is pointless. But there was a point stated in the question: "What I'm trying to do is reduce the memory requirement." In retrospect, I wish I hadn't offered the database suggestion. Not because it's not a reasonable comprimise (It is reasonable) , but because the OP undoubtedly already knows his options with regards to databases, being a 'Team Sybase Member'.


Dave

In reply to Re^3: two hashes occupying the same space by davido
in thread two hashes occupying the same space by jfroebe

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