“Facebook said the results of using HipHop have been dramatic. CPU usage on Facebook servers has dropped by an average of 50 percent as the HipHop PHP engine reduced the load on Facebook’s infrastructure.”
The article isn’t that detailed but from the following quote:
“This is not an extension to PHP — this is pretty different,” Recordon said. “Right now, the process is once you build and compile HipHop, it comes with a tool that will go through the transformation process and output the binary, and that’s what you actually use to run it.”
And the fact that they’ve removed Apache and uses an own web server. I start to wonder if what they do is actually take the PHP source code and compile it to get one binary that is both the web server and the application in one.
PHP is an interpreted script language so what normally happens is that PHP takes the source file and reads it line by line as it’s executing it. If they’ve bypassed this step completely by pre-compiling the script file into machine code that would explain the reduced CPU usage.