I was on shared hosting and all of a sudden my host kept shutting down my account saying that index.php is hogging all the resources. I did everything I could - disabled non-essential plugins, ran W3 Total Cache fully set up, running a CDN, optimized as much as I could and it was still happening.
I ended up switching to a new host on a VPS, optimized it even more, running memcached, etc, and the same problem is happening. The site keeps going down a few times a day, server reboots, and it's back up shortly.
Why does this keep happening? I can't find out what's going on, I just keep seeing index.php taking up a ridiculous amount of resources over a few hours and shutting down.