Which ACID property guarantees that changes are preserved across crashes?

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

Answer: (D)

Durability is the property that guarantees committed changes survive crashes or power failures. When a transaction commits, its effects are written to non-volatile storage (often with a commit log or write-ahead log) and flushed to disk. This means that even if the system crashes immediately after the commit, recovery can use the durable records to reconstruct the committed state, so the changes are not lost. This is different from atomicity (all-or-nothing behavior within the transaction), consistency (data respects constraints), and isolation (transactions don’t interfere with each other). For example, after a money transfer commits, the updated balances remain correct after a restart because those changes were durably recorded.