How to Fix Slow Code in Ruby

At Shopify, we believe in highly aligned, loosely coupled teams to help us move fast. Since we have many teams working independently on a large monolithic Rails application, inefficiencies in code are sometimes inadvertently added to our codebase. Over time, these problems can add up to serious performance regressions.By the time such performance regressions are noticeable, it might already be too late to track offending commits down. This can be exceedingly challenging on codebases with thousands of changes being committed each day. How do we effectively find out why our application is slow? Even if we have a fix for the slow code, how can we prove that our new code is faster?.