A Level Computer Science OCR Practice Exam

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Which aspect of ACID ensures that once a transaction has completed, it will persist even in the case of a system failure?

Atomicity
Consistency
Isolation
Durability

The correct answer is: Durability

The correct answer, Durability, refers to the property of ACID that guarantees once a transaction has been committed, it will remain in the system even in the event of a failure, such as a power outage or crash. This means that the changes made by the transaction are permanent and will survive subsequent system failures. When a transaction is marked as complete, the system ensures that the state resulting from that transaction is stored safely, often through mechanisms like logging and backups, so that it can be recovered in the case of a failure. This provides confidence to users and systems that their data is secure after a transaction. The other concepts of ACID contribute to reliable transaction processing but do not specifically address the idea of data persistence after a transaction has been completed.