Performance optimization is tough and it can even become a nightmare if you are not prepared. Consider the fact you should do it on a live system. Modern websites are built upon completely new tooling: new programming languages, new platforms, new frameworks. Performance engineers struggle to keep up with the fast pace of these emerging technologies. Fortunately, we already have the DTrace framework brougth to existence by engineers of Sun company (now extinct). Although Sun Solaris-related tecnologies are not commonly used nowadays, our company uses the wonderful DTrace stack to speed up performance analyzis of middle to big live systems. We are going to present two our cases, one PHP and on Ruby on Rails-based and explain how DTrace helped us to find and eliminate bottlenecks.