A Level Computer Science OCR Practice Exam

What happens if a transaction in a database processing fails?

1. Only the last operation is undone

2. The entire transaction is rolled back

3. All operations remain committed

4. It is logged but not undone

The correct answer is: The entire transaction is rolled back

When a transaction in a database processing fails, the entire transaction is rolled back. This means that all operations that were part of the transaction are undone, restoring the database to its state prior to the transaction. This ensures the integrity and consistency of the database, preventing partial updates that could lead to data anomalies or corruption. The rollback process is crucial in transaction management systems, especially within ACID (Atomicity, Consistency, Isolation, Durability) properties. Atomicity ensures that transactions are all-or-nothing; they cannot be partially completed. Therefore, if any part of the transaction fails, the system must revert to the original state to maintain data consistency. In contrast, if only the last operation were undone, or if operations remained committed, there could be inconsistencies in the data leading to further complications. Moreover, merely logging the transaction without executing a rollback does not resolve any issues that may arise from failures. Thus, the ability to roll back a failed transaction entirely is essential for maintaining the robustness of a database management system.