A little truth that not everybody knows is that you’re unlikely to know what happens in your application until you actually look at your application while it is running. It doesn’t matter if you are the developer that wrote most of the application code, todays applications might be so complex that what happens behind the scene is hard to picture.

A story that supports this statements happened a week ago, when I started looking into the code that performs the server side rendering of an application. “It’s straightforward and it works fine” I thought, “after all it’s less than one hundred lines”. But I was just guessing.

What I saw looking at the code was different from what I saw running the code with the proper investigation tools.

Long story short, this process allowed me to track a mistake I made that was hurting the application performance. Here is how I did it.