(Disclosure: I'm a Developer Advocate employed by Basho) Postgres is a better fit for most Ruby web applications. When you first launch your app, you'll have a

(Disclosure: I'm a Developer Advocate employed by Basho) Postgres is a better fit for most Ruby web applications. When you first launch your app, you'll have a tiny handful of users and won't have any problems fitting it in a free Heroku instance on the free 5MB shared Postgres, and the compromises you'd have to make with your data model to fit a database like Riak aren't going to pay off until you get enormous. Postgres and ActiveRecord get the job done quickly and without fuss, and allow you to launch quickly and see how your app is received. You can always scale later: https://gettingreal.37signals.com/ch04_Scale_Later.php https://gettingreal.37signals.com/ch04_Scale_Later.php