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I'm not familiar with RethinkDB, but I have read the H-Store paper and I think some of its optimizations are applicable to RAM but not SSD. SSDs are much faster than disk, but I don't think they're fast enough that you can afford to eliminate caching or locking. In particular, good SSDs are internally parallel and require multiple concurrent I/Os for good performance, so you'll probably have to execute multiple transactions concurrently.

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Well, if an average random access to disk is ~5ms, and an X25 Intel SSD is ~500 microseconds, then we're already talking a 10x difference and that's for a 'consumer grade' SSD. I'm sure the latency will come down over time as well. If you look at some of the PCI-E SSD solutions, then we're dipping below 100 microseconds, which means we're into 50-60x difference.

Indeed. Even with ram, concurrency is optimal on many server architectures. See NUMA, http://en.wikipedia.org/wiki/Non-Uniform_Memory_Access

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