Php apc opcode cache - caching whole files vs variables

Question

Are entire php files added to apc just by using and enabling it?

I understand how fetch and store works with variables, but when should this be used? Is the caching of whole files done automatically? If a variable is cached - should it only be a global variable or a user-specific variable?

Answer 1

Generally, you should cache Database responses that don't need to be updated frequently, but is accessed frequently. This data need not be from a database — could also be from a file or any type of data store. The key is to feed the most popular things from cache/memory to avoid i/o which is costly.

Take a look at this answer for a good explanation of Opcode caching. Opcode caching basically just stores your PHP file on memory, so that it can be interpreted quicker when run.

APC works automatically, and detects changes to your file to see if it needs re-caching. Quoting from the above answer:

The apc.stat option defines whether APC should examine the last modification date/time of a file to decide between using the opcodes from RAM, or re-compiling the file if it is more recent that the opcodes in RAM.

Also, to answer your global vs user specific question. It all depends on exposure, you should cache anything with large amounts of exposure. But generally user-specific data will have less exposure than global data.