Measuring Rails Overhead

We all know that using Ruby on Rails is slower than just plain Rack. After all, Rack is the simplest, most bare-bones web interface in Ruby, unless you’re willing to do without compatibility between app servers (or unless you’re writing your own.)But how much overhead does Rails add? Is it getting less as Ruby gets faster?I’m working with a new, simpler Rails benchmark lately. Let’s see what it can tell us on this topic.