I'm at Surge, this week, where I just listened to Baron Schwartz give a talk about scalability and performance. As usual, Baron was careful to distinguish between performance (which is how fast it is) and scalability (which is how much faster you can make it by adding more resources). One of the things Baron talked about was Neil Guenther's Universal Scalability Law, which attempts to model the behavior of complex systems (such as database systems) as you add threads, or nodes, or users.