In several recent posts: It’s LEMP not LAMP! and Amazon EC2 Shoutout! I've discussed how I switched from a shared hosting account with GoDaddy to a dedicated Micro instance with Amazon. At the same time I decided to go out and try nginx (pronounced Engine-X) and remove Apache from the equation.
This saw some incredible results. However, several times since switching I've run into several database issues where it appears Mysql runs out of memory! Performing a top command shows over 15 mysql processes running at anyone giving time each taking up to 10% of the memory. On a micro instance I only get 600mb, so this adds up quickly!