One of the worst types of errors to track down, I think, is one that happens in a blue moon and doesn’t seem to happen in response to anything particular. Here, I’ve been trying to hunt down why, every month or two, WordPress starts serving nothing but blank pages, yet not logging any errors, and why restarting Apache fixes the problem.

The main page isn’t affected, since it doesn’t use WordPress or APC (it’s some custom code I wrote that goes right to the database), but every other page on the site comes up blank. Server-wise, everything is fine: no parameters at all are different. The load’s low, nothing’s been changed, memory usage is fine, and so on. The logs seem to suggest that pages are being served just fine.

I just made a small bit of progress: logging into the APC (Alternative PHP Cache, not the UPS company) console and flushing the opcode cache fixes the problem. I always had a hunch it involved a cache somewhere, but I looked more at WP Super Cache than at APC. I still haven’t solved the problem, but now I know where to look.