Cassandra, mongodb or couchdb for Ruby on Rails [closed]

To make an informed selection, you'll really need to know your data model. MongoDB and CouchDB are document-oriented data stores. Cassandra is quite different, it is a bit more special-purpose and its distributed design is its strength. It's more of a distributed key/value store but with slicing, timestamp sorting, range queries, with limited data types. If you had a huge amount of data and knew exactly how it needed to be indexed for retrieval, Cassandra might work. Mongo and Couch are better for ad-hoc queries, and for example an AR replacement for a Rails app.

As far as popularity, I'd say MongoDB is currently more popular with Rubyists, but in general CouchDB seems to have more mindshare and a lot of momentum.

See also http://nosql-database.org/ for more information on the differences.

I personally used "mongoid" recently and it was working really good. One thing to keep in mind is that they are more active in Rails 3.0 branch so not all features listed on their website work in Rails 2.x (for example references). I also tried to use "Devise/Warden" for authentication and it worked seamlessly in Rails 3.0 but did not have support for Rails 2.x + mongoid (although mongomapper was supported)