Modern PHP

Chapter 11. Profiling

Profiling is how we analyze application performance. It is a great way to debug performance issues and pinpoint bottlenecks in your application code. In other words, if your application is slow, use a profiler to figure out why. Profilers let us traverse the entire PHP call stack, and they tell us which functions or methods are called, in what order, how many times, with what arguments, and for how long. We can also see how much memory and CPU are used throughout the application request lifecycle.

When to Use a Profiler

You don’t need to profile your PHP applications immediately. You only profile PHP applications if there is a performance issue that is otherwise hard to diagnose. How do you know if you have a performance issue? Some issues are obvious (e.g., a database query takes too long). Other issues may not be as obvious.

You can detect performance issues with benchmarking tools like Apache Bench and Siege. A benchmarking tool allows you to test your application performance externally, much like an application user would with a web browser. Benchmarking tools let you set the number of concurrent users and total number of requests that hit a specific application URL. When the benchmarking tool finishes, it tells you the number of requests per second that your application sustained (among other statistics). If you find a particular URL sustains only a small number of requests per second, you may have a performance issue. If the performance issue is ...