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Lesson plan 35: Capacity and multitenancy
Convert workload demand into CPU, memory, storage, and network budgets.
Placement: Part 6: Scaling execution and state delivery.
Prerequisites: Lesson 34: Tail latency and overload, plus the earlier dependency chain.
Learning outcomes
- Convert workload demand into CPU, memory, storage, and network budgets.
- Explain hot keys, tenant quotas, noisy neighbors, and failover headroom.
- Evaluate autoscaling against a particular bottleneck and distinguish isolation from average utilization.
- Separate a general mechanism, a documented implementation choice, and an illustrative numerical assumption.
Teaching sequence
- Establish the motivating situation: One tenant’s scan and compaction workload pushes unrelated transactional tenants beyond their latency targets.
- Introduce the vocabulary and the correctness obligation before an optimization. Define CPU, memory, storage.
- Develop the mechanism: Build a per-operation resource vector and distinguish spare capacity from isolation.
- Follow the complete worked example: 80000 operations/s at 40 microseconds CPU each needs 3.2 fully utilized CPU-seconds per second. Explain the assumptions, intermediate units, and limiting interpretation.
- Extend the scenario to changed load, skew, or failure, explaining network, hot keys, isolation, quotas, noisy neighbors, autoscaling.
- 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 resource-budget table and node-loss scenario show how nominal spare capacity disappears during failure and maintenance. 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.