intermediate~2h
Undo, Redo & How Durability Actually Works
The mechanics behind two guarantees you've likely taken for granted: that a rollback can undo your changes, and that a committed transaction survives a crash.
Learning objectives
- Explain what undo data is used for, beyond just ROLLBACK
- Explain how undo data enables read consistency for other sessions
- Explain what redo logs record and how they enable crash recovery
- Connect redo logging to the Durability guarantee in ACID without re-teaching ACID itself
- Distinguish undo (logical, reversible) from redo (physical, replayable) by purpose
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Undo, Redo & How Durability Actually Works