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Lesson plan 17: Execution engines
Compare iterator, vectorized, compiled, parallel, and asynchronous execution paths.
Placement: Part 3: Turning requests into execution.
Prerequisites: Lesson 16: Cost-based planning, plus the earlier dependency chain.
Learning outcomes
- Compare iterator, vectorized, compiled, parallel, and asynchronous execution paths.
- Calculate the amortization threshold for batching or compilation and identify first-result costs.
- Explain SIMD, intermediate materialization, scheduling, and memory bandwidth as separate limits.
- Separate a general mechanism, a documented implementation choice, and an illustrative numerical assumption.
Teaching sequence
- Establish the motivating situation: A short lookup pays compilation cost while a long analytical scan benefits from specialized loops.
- Introduce the vocabulary and the correctness obligation before an optimization. Define iterator, vectorized execution, compilation.
- Develop the mechanism: Compare control flow and data flow through row-at-a-time, batched, and compiled pipelines.
- Follow the complete worked example: A 2 ms compilation cost amortizes over 1 million rows as 2 ns per row. Explain the assumptions, intermediate units, and limiting interpretation.
- Extend the scenario to changed load, skew, or failure, explaining SIMD, parallel execution, async execution, materialization.
- 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
An execution pipeline contrasts tuple-at-a-time dispatch with a block of values and marks where state materializes or crosses a worker boundary. 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.