I have a blog running on a FreeBSD 8.1 system with PHP 5.3.5 and APC 3.1.6.
At first everything seemes fine, but after a while (about 18-24 hours) all pages are served blank, and with a status code of 500. There is nothing in either the vhost, or the global Apache error logs, and PHP doesn’t log anything either. The requests are only logged in the access log, with a 500 code. All the other vhosts on the server run fine while the blog is down. An Apache restart fixes the problem.
PHP error logging is enabled (the deprecated functions are logged) while the site is working.
Disabling APC for this vhost solved the issue, but that is not a long term solution, because the CPU load is roughly doubled this way.
Is this a WP issue, or an APC bug?
EDIT
Forgot to add WP version, it is version 3.1.3
Raising apc.shm_size from default value 32M to 256M in php.ini seems to do the trick for us.
edit: raising that value is not a bad idea, however it does not solve the issue in the long term. We are now considering removing either APC or Super Cache…