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Lesson plan 06: Performance reasoning
Calculate latency budgets, utilization, throughput ceilings, and in-flight work under stated assumptions.
Placement: Part 1: Foundations: understanding work, time, and resources.
Prerequisites: Lesson 05: Application protocols and remote calls, plus the earlier dependency chain.
Learning outcomes
- Calculate latency budgets, utilization, throughput ceilings, and in-flight work under stated assumptions.
- Interpret tail percentiles and queueing models without treating model assumptions as measurements.
- Construct a benchmark comparison that preserves correctness, hardware, load, and timing boundaries.
- Separate a general mechanism, a documented implementation choice, and an illustrative numerical assumption.
Teaching sequence
- Establish the motivating situation: A benchmark looks healthy because its clients stop generating traffic while the server is slow.
- Introduce the vocabulary and the correctness obligation before an optimization. Define latency budgets, throughput, percentiles.
- Develop the mechanism: Derive a resource ceiling, apply queueing assumptions explicitly, and compare open-loop with closed-loop measurement.
- Follow the complete worked example: At service rate 10000/s and arrival rate 9000/s, M/M/1 mean response is 1 ms. Explain the assumptions, intermediate units, and limiting interpretation.
- Extend the scenario to changed load, skew, or failure, explaining queueing, utilization, Little’s Law, Amdahl’s Law, coordinated omission.
- Connect the mechanism to a documented implementation and an alternative with a different workload fit. Close by stating the remaining cost and the next lesson dependency.
Required chapter material
Use a complete execution trace or worked calculation, supported by an annotated static diagram or table. Include language-neutral pseudocode or labeled SQL when it clarifies the mechanism. State preconditions, ownership, visibility, and failure boundaries for algorithms. Describe operational costs as well as the normal path. All questions raised in the narrative must be resolved in the text.
Visual explanation
A queue-and-server diagram separates waiting from service, and a utilization table shows the nonlinear rise in delay near saturation. The accompanying prose explains the arrows, state changes, or table entries so the lesson remains understandable in a plain Markdown reader.
Editorial checks
Confirm that the numerical example agrees with its units and assumptions. Check that a faster path preserves the stated contract, or explicitly identify the changed guarantee. Keep hypothetical figures separate from product measurements. Explain both an appropriate use and a limitation of the case design. Check terminology against the glossary and links against the course index.