The Mythical IO-Bound Rails App

+1 for any app with simple or properly optimized DB queries, time in Ruby rendering output is the bottleneck.

For anyone who doubts, either set up New Relic or emit timestamps before your controller hands of to the view and in Rack before passing the output back up the middleware stack.

If your time isn't being eaten up in output rendering and if you're using an RDBMS, I suggest getting the generated SQL from your log and running `explain` to find where the query plan is suffering. Sometimes, changes in the shape of the data can lead to the query planner to make choices that you didn't optimize for that can negatively impact DB performance.

If the ORM is bad enough, it can easily overwhelm the language being slow ;-)