How COMMIT and ROLLBACK Work
A transaction groups multiple updates into a single unit. The updates are not yet finalized, and stay invisible to others until then. It ends either by COMMIT, which finalizes every update, or by ROLLBACK, which undoes every one of them — a property called atomicity. ACID stands for the four properties a transaction should satisfy: atomicity, consistency, isolation, and durability.
GOAL
Explain how a transaction finalizes or undoes a group of updates as a single unit, and what atomicity means in ACID.
Choosing to end with COMMIT, what are the final balances of A and B?