[OT] Efficient file structure for very large lookup tables?

[H. S. Teoh]

Another OT thread to pick your brains. :)

What's a good, efficient file structure for storing extremely large
lookup tables? (Extremely large as in > 10 million entries, with keys
and values roughly about 100 bytes each.) The structure must support
efficient adding and lookup of entries, as these two operations will be
very frequent.

I did some online research, and it seems that hashtables perform poorly
on disk, because the usual hash functions cause random scattering of
related data (which are likely to be access with higher temporal
locality), which incurs lots of disk seeks.

I thought about B-trees, but they have high overhead (and are a pain to
implement), and also only exhibit good locality if table entries are
accessed sequentially; the problem is I'm working with high-dimensional
data and the order of accesses is unlikely to be sequential. However,
they do exhibit good spatial locality in higher-dimensional space (i.e.,
if entry X is accessed first, then the next entry Y is quite likely to
be close to X in that space).  Does anybody know of a good data
structure that can take advantage of this fact to minimize disk
accesses?


T

-- 
Computers are like a jungle: they have monitor lizards, rams, mice, c-moss, binary trees... and bugs.