You've written a not so trivial PHP application and your web site is visited more and more frequently, 1 time per second, 10 times, 20 times per second, more. You transfered your database to a second mashine but still your webserver performance breaks down at 25 request per second. You install a byte code cache like the APC or XCache but your servers still do not deliver more than 30 or 40 requests. What now?
You may spend some weeks to refactor your whole software. Or you invest 30 minutes to fix your file inclusions and you win some 100% performance - even more.
The recipe is easy - watch your server process with strace, take care on file stats and try to reduce it to zero:
- reduce your include_path to a single entry or don't use it at all
- include or require absolute paths
- ensure that each try to include a file is a hit
- avoid file_exists(), is_file(), is_dir(), is_link() etc.
- avoid autoloading
That's it.
Each file system access forces the operating system to switch context and wastes a huge number of CPU cycles. If you have a long include path and the file to include is found at the end you have a lot of useless file stats. Even the byte code cache cannot protect you from this since it stores only files found, not files that do not exist. For each non existing file all the stats and lookups take place again and again. This is what your CPU works for, not your business logic.
Stats are evil.
