A financial database system ensures that once a transaction is committed, the data changes are permanently stored and will survive any subsequent system failure, such as a power outage or crash. Which property of ACID transactions does this describe?
Durability ensures that once a transaction is committed, its effects are permanent and survive system failures.
Why this answer
D is correct because durability guarantees that once a transaction is committed, the changes persist permanently, even in the event of a system failure like a power outage or crash. In SQL Server, this is implemented via the write-ahead log (WAL) and checkpoint processes, ensuring committed data is flushed to disk before acknowledging success.
Exam trap
The trap here is that candidates confuse durability with atomicity, thinking 'permanent storage' relates to the all-or-nothing nature of a transaction, but atomicity only guarantees that partial changes are rolled back, not that committed data survives crashes.
How to eliminate wrong answers
Option A is wrong because atomicity ensures that a transaction is treated as an all-or-nothing unit, not that committed data survives failures. Option B is wrong because consistency ensures that a transaction brings the database from one valid state to another, preserving integrity constraints, not permanent storage. Option C is wrong because isolation ensures that concurrent transactions do not interfere with each other, not that committed data is durable.