Capstone Checkpoint

Explain compensation records, completed rollback, slot reuse, and model limits.

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

1. T1 commits key=10; T2 writes 99 and aborts; T3 commits 30; the engine crashes. What must recovery return?

Select one answer.

10, because T2 never committed 99, because redo includes all updates An absent key, because one transaction aborted 30, because completed rollback must not erase a later commit

2. A rollback reverses an update originally logged at LSN 8. What LSN should its compensating page write use?

Select one answer.

8 again A new LSN later than the current log end 0, because undo is not a write The page's previous LSN minus one

3. A transaction deletes key A, reuses its slot for key B, then aborts. The insertion of B must log which before-image?

Select one answer.

The actual tombstoned A record in that slot An empty record because B is a new key The final committed map of the entire database Only B's key

4. Why is rebuilding the index after rollback valid in this capstone?

Select one answer.

A map automatically survives crashes Index entries do not depend on slot contents The key-to-location index is derived by scanning live page records Recovery never changes record locations or visibility

5. What does a durable abort record prove?

Select one answer.

Every affected page has already been restored The transaction committed no changes, so no recovery is needed The transaction's records may be removed immediately Rollback has been requested; a completion marker is needed to prove it finished

6. Which guarantee fits the capstone's declared input model?

Select one answer.

Arbitrary concurrent writers need no locks Repeated crashes between atomic operations preserve completed serial transactions Recovery may be interrupted anywhere without extra bookkeeping Page writes may tear without checksums or recovery support

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