Amongst the ACID properties of a transaction, the 'Durability' property…
2005
Amongst the ACID properties of a transaction, the 'Durability' property requires that the changes made to the database by a successful transaction persist
- A.
Except in case of an Operating System crash
- B.
Except in case of a Disk crash
- C.
Except in case of a power failure
- D.
Always, even if there is a failure of any kind
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Correct answer: D
Answer: Always, even if there is a failure of any kind (subject to practical limitations).
Explanation:
Definition: Durability ensures that once a transaction commits, its effects are permanently recorded and will survive subsequent system failures.
Failures covered: Typical failures include process crashes, operating system crashes, and power failures. The DBMS uses recovery protocols (for example, write-ahead logging and careful flushing to non-volatile storage) so committed data can be restored after restart.
Practical limitation: Durability cannot protect against complete physical destruction or loss of the storage medium (for example, severe disk hardware failure, fire, or theft). To tolerate such events you need redundancy strategies such as replication, RAID, off-site backups, or distributed storage.
Typical mechanisms: write-ahead logging, commit record flushes, checkpoints, and replication help the DBMS ensure durability in the face of crashes.
Simple example: If a transaction commits and the DBMS has flushed the necessary log records and data to stable storage, then a subsequent power outage will not remove that transaction’s effects; on restart, recovery makes those changes visible.