When you’re building a new Rails app, ActiveRecord’s defaults will take you far. Querying with .where, inserting with .save — it’s all so easy, and it’s fast enough. But when a page of mostly simple content takes a second or more to come back from the server, that’s when you know you’re going to have to spend some time on performance. Luckily, you don’t have to go too far from the simplicity of Rails to see drastic improvements in your app’s response time.