Which ACID property ensures that a transaction’s operations are all completed or none are?

• A. Atomicity
• B. Durability
• C. Consistency
• D. Isolation

Answer: (A)

All-or-nothing execution of a transaction is what Atomicity guarantees. This means a transaction is treated as a single indivisible unit: either every operation in it succeeds and the changes are committed, or if any part fails, none of the changes take effect and the system is rolled back to the state before the transaction began. This prevents partial updates, such as transferring money where only one account is debited. In practice, recovery mechanisms and logging ensure that either the entire set of operations is applied or none of them are. Durability is about preserving committed changes after a crash, Consistency ensures transitions lead to valid states, and Isolation prevents concurrent transactions from interfering with each other.