"performance impact" when using a 20K lines single class

Question

This question was asked here before, but none of the answers really tried to answer the actual question asked, so I'm asking it in a different way. Is loading a single class of 20,000 lines with 100s of functions more resource intensive in any way than breaking up the code to smaller classes with fewer functions each and loading these smaller classes as needed?

Answer 1

The larger a script or class is, the more memory this uses per instance. Out of the box, PHP doesn't have a way to share the memory space of libraries and classes, so creating massive scripts for a website is not a great idea.

The typical approach should be to break classes down into blocks such that you need only include per script what you actually need to run that script.

Also, it's unlikely to cause you performance problems unless you've got a huge amount of traffic - and then you could probably fix your problems easier than refactoring classes.

When a script is loaded, it requires a fixed amount of memory to parse it. The larger it is, the more memory it requires. Next, the script itself is executed, running any top-level code (not in a class or global function). If that includes any require/include statements, those scripts are loaded (if necessary). If it creates objects, that takes more memory.

However, the size of each instance of the class is affected only by the data it stores. This correction aside, the advice here is spot on: split your classes based on responsibilities. The reason for this has also to do with ease of development than performance. Say you have one monster class filled with static methods. If your application uses most of those methods for each request, splitting it will have no performance benefit because both scripts will end up being loaded anyway. But if you can group the methods into logical subsystems, they will be easier to understand and work with.

Answer 2

One big class require single cycle to compile into binary code (op-code).

Many smaller classes using lesser memory but require more compilation, and the memory use for compilation will be accumulated.

Is really depend how many classes/files has been included in run-time.

So, solution for this, break into multiple classes and use APC or equivalent.

PS: the memory consumption for the big file is much smaller, because PHP do not need to re-compile the source into op-code (if you reluctant to break the big class into smaller)