ACID transactions and all-or-nothing updates

≈ 45 min

ACID transactions and all-or-nothing updates

A transaction is a protected unit of work in a database. When an online shop records a payment and reduces stock, the two changes belong together. If power fails after one change but before the other, the system needs a rollback rather than a half-finished story. Atomicity means all-or-nothing; consistency preserves stated rules; isolation manages concurrent work; durability keeps committed results after failure.

Transactions are not a substitute for correct business rules. A transaction can reliably commit an incorrect update if the logic is wrong. First state the invariant, such as stock must not be negative or a payment cannot be recorded twice. Then decide which reads and writes must happen as one unit and what the system does when a conflict or error occurs.

Worked reasoning. A learner buys the last laboratory kit. The database checks quantity, inserts an order, decreases stock and records payment inside one transaction. If the payment gateway rejects the payment, the order and stock update roll back. If two buyers try at once, isolation or a locking rule prevents both from receiving the single item.

Exam lens. Explain transactions using a concrete before-and-after invariant. Listing ACID letters without an example earns less than showing what inconsistency is prevented.

Which statement is the most defensible principle for ACID transactions and all-or-nothing updates?

A transaction groups related changes so partial failure cannot leave records disagreeing.

Treat an implementation detail as more important than the stated rule.

Assume one successful run proves the system is correct in every case.

Avoid recording assumptions, limits or failure conditions.

Enter the key term for ACID transactions and all-or-nothing updates. Which transaction property means a grouped update either fully succeeds or fully fails?

A payment record exists but the subscription entitlement was not granted after a crash. Which transaction property was violated in the visible outcome?

Atomicity was not achieved because the linked updates were left only partly applied.

Use a larger class or broader permission without stating a rule.

Trust the first output and skip a boundary or failure check.

Hide the decision so affected people cannot inspect it.

Name the concise safeguard or principle that completes this lesson’s scenario: A payment record exists but the subscription entitlement was not granted after a crash. Which transaction property was violated in the visible outcome?