When Facebook moved its servers to HipHop for PHP – the code transformer it built to convert PHP into optimized C++ – the company’s average CPU usage dropped by 50 per cent. And after six months of additional engineering, the tool was about 1.8 times faster.

Now, after another six months, the company says, it has improved performance another 1.7 times. But this is more than just self-congratulation. The project is open source, and it has been open since Facebook first switched its servers to HipHop in February 2010.

via Facebook HipHop serves 70% more traffic on same hardware • The Register.