Each header compile once and only once. Store that into memory instead of the disk.
As you probably already know, PHP is an interpreted language (unlike, say, Java or C++). Whenever a client requests a PHP page, the server will read in the source code of the page, compile it into bytecode and then execute it. In the normal scenario, this process is performed on every request…although PHP is so speedy that you probably won’t even notice it!
If you’re running an application or Web site that has many hundreds or thousands of requests coming in per minute, though, you’re going to want to speed things up as much as possible. And that’s where APC comes in. In the words of its Web site, APC is “a free, open, and robust framework for caching and optimizing PHP intermediate code.” Very simply, APC caches the compiled output of each PHP script run and reuses it for subsequent requests. This reduces the time and processing cycles needed to fully satisfy each request, leading to better performance and lower response times.
PHP code accelerators do the bulk of their magic transparently by storing compiled versions of PHP scripts on disk or in shared memory in order to skip the compiling step with each request.