8. Performance

An ounce of performance is worth pounds of promises.

—Mae West

It’s about time.

Performance, that is: It’s about time and the software system’s ability to meet timing requirements. When events occur—interrupts, messages, requests from users or other systems, or clock events marking the passage of time—the system, or some element of the system, must respond to them in time. Characterizing the events that can occur (and when they can occur) and the system or element’s time-based response to those events is the essence is discussing performance.

Web-based system events come in the form of requests from users (numbering in the tens or tens of millions) via their clients such as web browsers. In a control system for an internal combustion ...

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