performance hit with on demand loading of class files

Question

In my recent projects a decided for a lazy, on demand load of class files with an autoloader. What is the performance hit of using an autoloader pattern for including class files as opposed to including the needed class files or all class files? Will it impact precompiling and caching?

Answer 1

In the majority of configurations, it will give a performance boost.

• With just "out of the box" PHP, every file is compiled on demand when you include it. If you include every file on every request, every file is compiled on every request.
• With OpCache enabled, each file is cached into shared memory when first compiled. However, that memory may get full, and there may be files that you never actually use, so compiling based on usage is still likely to be better.
• With preloading, you can pre-populate OpCache's cache of compiled files. Classes from preloaded files will automatically be available to all processes anyway, so just won't trigger the autoloader.

The only time an autoloader could be costly is if you have multiple places that the same class could be defined, and the autoloading function checks the disk for which ones exist. That's why Composer has options to optimize its generated autoloading routines. If you're not using Composer already, I highly recommend you do so.