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Lesson plan 19: Atomic transactions and logging
Define transaction states and distinguish execution, commit decision, durable acknowledgment, and visibility.
Placement: Part 4: Transactions, concurrency, and recovery.
Prerequisites: Lesson 18: Computation boundaries, plus the earlier dependency chain.
Learning outcomes
- Define transaction states and distinguish execution, commit decision, durable acknowledgment, and visibility.
- Explain undo, redo, and WAL ordering under explicitly stated buffer policies.
- Follow a crash at each boundary without committing an incomplete logical transaction.
- Separate a general mechanism, a documented implementation choice, and an illustrative numerical assumption.
Teaching sequence
- Establish the motivating situation: A transfer debits one account just before a crash; recovery must not preserve half a transfer.
- Introduce the vocabulary and the correctness obligation before an optimization. Define transaction states, commit boundaries, undo.
- Develop the mechanism: Define private versus installed writes; distinguish a durable commit decision from page installation.
- Follow the complete worked example: A batch of 40 commits sharing a 2 ms flush amortizes flush work to 50 microseconds per commit. Explain the assumptions, intermediate units, and limiting interpretation.
- Extend the scenario to changed load, skew, or failure, explaining redo, WAL, failure ordering.
- 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 transaction-and-log timeline labels update records, durable log position, commit record, page write, and reply, with a failure interpretation for each gap. 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.