Buffer Pool Checkpoint

Trace pin counts, recency, dirty state, and the WAL boundary.

Get every question correct to pass this checkpoint. You can review feedback, revise your answers, and submit again.

1. Capacity 1: fetch A, fetch A, unpin A, fetch B. What happens on the final fetch?

Select one answer.

A is evicted clean The fetch fails because A still has one pin The second fetch of A created another frame A becomes dirty and is evicted

2. Capacity 2: fetch/unpin A; fetch/unpin B; fetch/unpin A; unpin B again; fetch C. Which page is evicted?

Select one answer.

A, because B was unpinned last Neither, because both are pinned B, because only fetch changes recency C, because it is newest

3. A is unpinned with dirty=true, later fetched, then unpinned with dirty=false. Its next eviction reports:

Select one answer.

Dirty=true; the later unpin does not undo the earlier modification Dirty=false; the last flag wins Dirty=false; fetching implicitly flushes the page No eviction is permitted for dirty pages

4. The oldest resident page is pinned; the next oldest is unpinned and dirty. A miss fills no free frame. What does this simulator do?

Select one answer.

Evicts the oldest page regardless of pin count Fails because the only unpinned page is dirty Clears the oldest page pin count Evicts the next oldest page and reports its dirty flag

5. In a real WAL-backed engine, a dirty page has pageLSN=42 while the durable log ends at 39. Before writing that page, the engine must:

Select one answer.

Write the page first, then flush the log Make WAL durable through at least LSN 42 Wait for every transaction in the database to finish Reset pageLSN to 39

6. A solution returns all expected eviction IDs and dirty flags. Which property remains outside what this API can verify?

Select one answer.

That a pinned frame was not evicted That fetch updates recency That WAL was flushed before dirty page bytes reached storage That earlier evictions are retained when a fetch fails

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