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Lesson plan 09: Memory and buffer management
Trace a page from cache lookup through pinning, modification, writeback, and eviction.
Placement: Part 2: Representing and locating data.
Prerequisites: Lesson 08: Physical representation, plus the earlier dependency chain.
Learning outcomes
- Trace a page from cache lookup through pinning, modification, writeback, and eviction.
- Explain how replacement, prefetching, and scan behavior interact with a working set.
- Compare buffer-pool ownership with page-cache, direct-I/O, and memory-mapped approaches.
- Separate a general mechanism, a documented implementation choice, and an illustrative numerical assumption.
Teaching sequence
- Establish the motivating situation: A reporting scan evicts a small hot transactional working set and raises latency.
- Introduce the vocabulary and the correctness obligation before an optimization. Define buffer pools, eviction, pinning.
- Develop the mechanism: Trace hit, miss, pin, eviction, writeback, and I/O completion; separate replacement from durability ordering.
- Follow the complete worked example: 98% hits at 1 microsecond and 2% misses at 200 microseconds average 4.98 microseconds. Explain the assumptions, intermediate units, and limiting interpretation.
- Extend the scenario to changed load, skew, or failure, explaining dirty pages, prefetch, direct I/O, mmap, working sets.
- 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 page lifecycle diagram marks clean, dirty, pinned, and evictable states and explains why dirty does not mean immediately replaceable. 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.