Constraints
The hardest thing about dealing with capacity is working with nonlinear effects. Our brains can subconsciously integrate differential equations fast enough to drive a car or catch a baseball. Somehow, though, whenever we start talking about capacity, everybody wants to fall back to linear projection. Have you ever been asked, “So, if we can handle 10,000 users at 50% CPU usage, we should be able to handle 20,000 users total, right?”
In every system, exactly one constraint determines the system’s capacity.[61] This constraint is whatever limiting factor hits its ceiling first. Once the constraint is reached, all other parts of the system will begin to either queue up work or drop it on the floor. For example, suppose that the constraint ...
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