Back in 2007 I wrote an article on how to port your PHP applications into C++ (in the Oct 2007 issue of PHP Architect), showing the speed-up and memory-usage benefits. It's a nice idea, though I've only done it in a production project once. The programmer man-hours is very rarely worth it.
Well, Facebook have gone and automated the process, calling it Hip-Hop. Over 90% of Facebook's (400 billion PHP-based page views every month) traffic is now running on their Hip-Hop system, i.e. on PHP pages that have been compiled into C++.
This is very interesting to me as I have recently been writing less and less in C++, more and more in PHP. Even a tree searcher for computer go I have been doing in PHP, as an experiment to see how it goes. On reflection that particular experiment is probably a failure - I need to set bits in a 32-bit or 64-bit integer and PHP puts a layer of abstraction in the way.
The main php script is very slow (its been running non-stop for 5-6 weeks so far, with months left to run) but ironically all that time is being spent in calling other applications (written in C++!) to do the hard calculations. However I've another script that analyzes the data, needing to hold it all in memory at once, and that is showing signs of cracking - I'm already having to set my memory_limit to 1.5G, and that will probably hit 4G when the other script has chomped through all my data.
Hip Hop might be my saviour.
P.S. PHP Architect magazine also think this is going to be a very important technology.