The most common problem that Ruby on Rails has with performance is a mis-use of the ORM layer (Active Record). People will call dependent objects in a loop not realizing what is happening between the application and the database. If you want a performant application instead of thinking only about your application code it is important to understand how what you are doing in the application layer is interacting with the database. In most production enterprise applications the amount of SQL calls made by the application per request/response is optimized. The reason for this is each SQL call will normally have to happen over the network and is generally slower than lines of code not making SQL calls. If you are experiencing performance issues with your Ruby on Rails application the best course of action may be to call a professional. Feel free to reach out to me directly at (973) 615-7955 for a free consultation on your app.