When Twitter faced early scaling issues, much was made of decisions to rewrite large portions of the Rails site in Scala.
Facebook however has decided to double down on PHP, releasing HipHop, a PHP source code transfomer:
HipHop programmatically transforms your PHP source code into highly optimized C++ and then uses g++ to compile it. HipHop executes the source code in a semantically equivalent manner and sacrifices some rarely used features — such as eval() — in exchange for improved performance. HipHop includes a code transformer, a reimplementation of PHP’s runtime system, and a rewrite of many common PHP Extensions to take advantage of these performance optimizations.
** Update **
We posted this blind yesterday when GitHub was unavailable. Looks like the repo isn’t public yet. Keep an eye out. GitHub explore shows five watchers…