On the Symfony blog today they've posted a use case that talks about Symfony meeting some high performance needs and some of the development that was done to make it happen.

For most people, using full-stack frameworks equals slowing down websites. At Octivi, we think that it depends on correctly choosing the right tools for specific projects. When we were asked to optimize a website for one of our clients, we analyzed their setup from the ground up. The result: migrate them toward Service Oriented Architecture and extract their core-business system as a separate service. In this Case Study, we'll reveal some architecture details of 1 Billion Symfony2 Application. We'll show you the project big-picture then focus on features we really like in Symfony2. Don't worry; we'll also talk about the things that we don't really use.

They start with some of the business requirements they needed to meet and how it influenced the overall architecture of the application. They cover some of the things they liked the most about using the framework including bundles and using the EventDispatcher component. Some example code is also included for the custom handling they created for routing, CLI commands and request handling. There's also a mention of using the Profiler, Stopwatch and Monolog trio to do some performance analysis on the resulting application. Finally, there's a brief mention of some of the tools they're not using and why (two of them): Doctrine and Twig.