How I can use partitioned database with RoR?

I want to ask this question with a specific example as I am looking for a concrete answer. :) Let's say I have a set of MySQL databases sharded on user_id. For example, all users who have ids 1-10000 will go into database D1, user ids with 10001 - 20000 will go into database D2 so on.. I have a model "User" in my RoR application. Depending upon the user_id for which information required this model should query appropriate database and return the results back. Can any RoR expert tell how to make it possible?

A related question is that, let's say I created N databases D1, D2 ... DN on the same box where MySQL running and a memcached cache layer infront of these databases. Does structuring开发者_如何学Python database in this way result in poor performance? (I am worried will there be many cache misses at DB layer and memcache layer.)

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I think that what you need is: http://partitioned.rubyforge.org/

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Take a look at the DataFabric gem which adds database sharding support to Active Record. It lets you do things like:

class User < ActiveRecord::Base
  data_fabric :replicated => true, :shard_by => :user_id
end

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What you're looking for is commonly called sharding. There's a pretty comprehensive article on wikipedia about it, which you should definitely read and a good article on the high scalability blog.

When it comes to sharding with rails I'd recommend the data fabric gem which supports application level database sharding as well as master/slave replication.

I hope this helps!