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Lesson plan 48: A complete architecture walkthrough
Carry explicit invariants through storage, logging, concurrency, replication, partitioning, and operational evolution.
Placement: Part 8: Architectural case studies and synthesis.
Prerequisites: Lesson 47: Contrasting workload priorities, plus the earlier dependency chain.
Learning outcomes
- Carry explicit invariants through storage, logging, concurrency, replication, partitioning, and operational evolution.
- Explain how the contended marketplace, multitenant service, and realtime world force different architectural branches.
- Produce a coherent capacity and failure argument that accounts for hot resources, durable acknowledgments, recovery, and overload.
- Separate a general mechanism, a documented implementation choice, and an illustrative numerical assumption.
Teaching sequence
- Establish the motivating situation: A reference engine evolves for a contended marketplace, partitionable SaaS, and realtime shared world.
- Introduce the vocabulary and the correctness obligation before an optimization. Define local storage, indexes, WAL.
- Develop the mechanism: Carry the same invariants through each evolution, state the new failure model, and explain when the architecture must diverge.
- Follow the complete worked example: 20000 transactions/s at 25 microseconds serial execution uses 50% of one execution resource before overhead. Explain the assumptions, intermediate units, and limiting interpretation.
- Extend the scenario to changed load, skew, or failure, explaining concurrency, replication, sharding, overload, operations.
- 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 staged reference-engine diagram adds one responsibility at a time, then branches into three workload-specific designs while retaining the same correctness obligations. 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.