Okay, I assume you are the original author of the topic. Looking the whole situation, I guess your primary problem is the ability to handle a large number of simultaneous users, correct? Databases like Postgres support this type of work, only if you had an operation of the size of Facebook you would begin to have problems. However, remember that the database is only part of the chain. You will need the application itself also has high performance (Ruby and performance are mutually exclusive). As an example, I have an application wherever although the client-server communication uses HTTP, the server is a highly specialized application that only pretends to be a "web server", receiving commands over HTTP but executing them in a specialized way and communicating directly with the database without intermediate frameworks. A bit strange, but works very well.