[jrockway]

Sounds like a good system. I've noticed that people tend to do things like shard based on even/odd, and then they realize that they need three databases.

I've never had either problem though... but if I ever need to shard I plan on doing it based on object ID. Then one request can be handled by multiple databases, "for free", increasing both throughput and response time.

[fizx]

Even/odd isn't the end of the world, but you would then be best jumping to mod 4.

[moe]

Actually for anonymous sharding (without a central index) a consistent hash is about the closest you can get to ideal distribution and flexibility. I haven't looked but I presume that's what mongo uses under the hood for their auto-sharding, too.