On his blog Frank De Jonge explains how he solved a performance problem in one of his projects.

Last week I took a deep dive into Symfony's Routing Component. A project I worked on suffered from a huge performance penalty caused by a routing mistake. This lead me on the path to discovering some interesting performance considerations. Some common practices align nicely with Symfony's optimisations, let's look into those.

https://blog.frankdejonge.nl/symfony-routing-performance-considerations/