Since any web-framework should be mostly IO-driven, the actual speed of the code matters very little as it will in most cases always be nothing compared to the actual IO-operation itself :/ In case you need certain code to run very fast, most people will write that in C/C++ and patch it into their solution, that's what we did in the Django-workshop I used to work in.
I thought Facebook mostly used C++ for their PHP VM? Facebook itself is alot of PHP, they also use Cassandra (Java DB) for inbox messages I believe.
No -- Facebook's PHP code is translated to C++ by HipHop and compiled into a monolithic binary, and Cassandra has largely been deprecated in favor of HBase.
"Facebook uses hphpi (and now hhvm) for day-to-day software development, but uses the HipHop compiler (hphpc) to create optimized binaries that serve the Facebook website. hphpc is in essence a traditional static compiler that converts PHP→AST→C++→x64."
I thought Facebook mostly used C++ for their PHP VM? Facebook itself is alot of PHP, they also use Cassandra (Java DB) for inbox messages I believe.