Paul Graham tweeted yesterday[1] an essay that the author had written which references kivaloo. At least, that's how I came to know about it yesterday.
I read the document on it, then tried to imagine what I would use it for, and couldn't really come up with a use case. I had trouble understanding where I would apply the 255 byte key to 255 byte value paradigm. I also didn't know how the benchmarks compared to similar applications.
255 bytes is obviously overkill for a key (a 32 or 64 byte secure hash of anything larger than 255 bytes can be assumed to unique), so it's just a question of what values are usefully in 255 bytes:
One thought that comes to mind is a distributed store with centralized master, 255 bytes is plenty for a hostname and resource ID.
If they're hashes, sure. If you want to answer range requests -- e.g. "give me everything starting with ABCDEF" -- you may have a less densely utilized address space (rather like IP networking has had).
My accounting database has keys of the form "usage/"<256-bit user ID><20-byte timestamp><64-bit machine ID><usage type string>. Not 255 bytes, to be sure, but not trivially short either.
