What do you need to take into consideration when deciding between MySQL and Amazon's SimpleDB for a RoR app?

Question

I am just beginning to do research into the feasibility of using Amazon's SimpleDB service as the datastore for RoR application I am planning to build. We will be using EC2 for the web server, and had planned to also use EC2 for the MySQL servers. But now the question is, why not use SimpleDB?

The application will (if successful) need to be very scalable in terms of # of users supported, will need to maintain a simple and efficient code base, and will need to be reliable.

I'm curious as to what the SO communities thoughts are on this.

Answer 1

The Ruby SimpleDB library is not as complete as ActiveRecord (the default Rails DB adapter), so many of the features you're used to will not be there.

On the plus side it's schemaless, scalable and works well with ec2.

If you're going to do things like full text search in your app then SimpleDB might not be the best choice, stick with AR + sphinx.