Help my client is complaining some parts of the application are slow. Now what? Profiling! What is profiling and how can we measure the performance of our application? There are several tools we can use. Once we have the tools, how do we approach profiling. What to look for. And caveats to avoid when profiling. To finish up, we should avoid that our client is complaining about performance, how can we pro actively use profiling to improve our application. When finished we will end up with a nice toolbox of profiling tools and good ideas how to do profiling and avoid some common mistakes that might distract you from the real optimisation.