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Idea 1: Log undo information
- Make sure committed records are on disk.
- Force change to disk before commit.
- Log undo records for all changes.
Recovery from crash
- A: was not committed, and is not on disk. Nothing to undo.
- B: was committed, and is not on disk. Skip the undo.
- C: was committed, and is not on disk. Skip the undo.
- D: was not committed, and is on disk. Undo the change.
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