I upgraded APC a couple of days ago and subsequently encountered a fatal error when trying to load my WordPress dashboard (but not the other wp-admin pages);
Fatal error: Call to undefined function wp_dashboard_setup() in wp-admin/index.php on line 15
Google confirmed the obvious; APC and WordPress didn’t get along (again), and the most common solution (next to switching from APC to XCache or eAccelerator) is to alter wp-admin/index.php by replacing
require_once(ABSPATH . 'wp-admin/includes/dashboard.php');
But I prefer not to change code that is bound to be overwritten at every WordPress upgrade and surely other PHP-apps suffer from the same problem, so instead I tweaked APC by adding the following line to my configuration:
This tells APC not to optimize include_once (it’s complicated). Why I have to explicitly specify this, if “0” is the default value anyhow, is beyond me though.