Efficiency for including files of functions (in PHP)

Question

If I had a large number of functions would it be better to keep them all in one large file or would it be better to separate them into several files of related functions. By better I mean more efficient for both maintainability and for the server processing the request.

For example right now I have all my files in a file named include.php. But would it be wiser to have an include file of includes like:

<?php
 include('/functions/user.php');
 include('/functions/admin.php');
 include('/functions/content.php');
 include('/functions/nav.php');
 include('/functions/database.php');
 include('/functions/other_junk.php');
?>

Answer 1

Definitely separate them, for maintainability sake. I doubt performance will suffer at all, but even if it does (just a teensy bit) you're better off writing maintainable, readable code.

Answer 2

You want to be sure you're using a PHP cache like XCache or APC. Your PHP files should then all be in memory and you shouldn't be worried about your includes hitting the disk at all.

I would definitely find it easier if you broke up like minded functions/classes into their own files.