The Facebook HipHop Open Source blog has posted a case study from Box about their migration to HHVM and some of the challenges and benefits that came along with it.

Reducing latency and increasing the capacity of our infrastructure have always been top priorities at Box. We strive to deliver the best possible user experience in the most efficient manner, and historically our choice of PHP hasn’t aligned well with these goals. I'm very happy to report that we've recently made very significant strides toward these two ideals by successfully deploying HHVM (the HipHop Virtual Machine) as the exclusive engine that serves our PHP codebase. In the rest of this post, I will detail how we use PHP, how HHVM works, the challenges we faced migrating to HHVM, and the remarkable performance wins it provides.

The post talks about how central PHP is to their overall technology stack and how, despite the work being put in, the processing of requests was starting to be a bit too much. In came the HHVM and some discussion about how it might be used there at Box. They started a yearlong effort to migrate their entire stack to HHVM especially since HHVM has almost reached parity with the PHP language itself. They talk some about the differences in design between the two and how the migration changed their deployment process. They also cover some of the other interesting things that come with a major migration including phased rollout and host-based conversion methods. Finally they share some of the statistics around the performance of the end result, including the better response times and reduced CPU graphs.