I spent the weekend fretting because one of my servers was basically being DOS'd by paying customers. During the outage I started thinking about the best way to scale and how I could make the code-base more efficient.
Linux top reported high load, in the 20's. Eventually I figured out that the server was having IO performance issues.
I wasted a bunch of time attempting to fight fires. After about an hour of that I decided to scale my VPS vertically by giving it an extra 256mb of memory and a larger swap file (256mb to 1024mb).
These two changes were surprisingly effective and the IO issues resolved. Apparently the server was starving for memory which caused the host to swap which brought things to a crawl waiting for IO.
Crisis averted for the moment. Now I am free to think clearly and engineer a proper solution instead of attempting to put out fires.
If you ever encounter a similar situation, attempt the simplest fix. There is no shame in throwing more money at a problem if it will buy you time. In this case, an extra $10.00 a month relieved the performance issues and bought myself some time, for the moment.