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4.1Performance design and capacity planning
Covers the distinction between response time, which drives user experience, and throughput, which measures processing capacity; the utilization (ρ)-to-wait-time relationship under the basic M/M/1 queueing model; and the judgment to diagnose bottlenecks and size capacity, built through business-requirement scenarios.
For a system architect, performance design is not the simplistic story of "add more servers and it gets faster." The response time a user experiences and the throughput the whole system can process per unit time are distinct metrics that are often in tension. Furthermore, without understanding a key property of queueing theory—that as the ratio of load to capacity rises, wait time degrades not linearly but sharply (nonlinearly)—an architect can be lulled into false reassurance by reasoning like "utilization is still only 50%, so there is headroom." This section builds the judgment to diagnose bottlenecks from load-test results and estimate the capacity needed, grounded in the response time/throughput distinction and the M/M/1 queueing model.
4.1.1Response time and throughput
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