Trending software
It's important to know how all these low-level tools work in order to use the more complicated ones, and when your system is in trouble, there's no substitute for the really detailed, second by second information tools like vmstat and top deliver. But most of the time, what people prefer is something more like what sar provides—a basic summary every few minutes—but with graphs, and if you can integrate in the database statistics too, so that everything is visible on a unified timeline, then you're really in a good position to note trends in your server's use.
