ITPEC FE Morning April 2018 Question 26
Which of the following properties of database transactions refers to the ability of the system to recover a committed transaction when either the system or the storage media fails?
Explanation
Durability — once a transaction has committed, its result must survive a system crash or a media failure.
The four ACID properties each guard against a different problem:
- •Atomicity: a transaction is carried out completely or not at all
- •Consistency: a transaction leaves the database in a state that satisfies its constraints
- •Isolation: concurrent transactions do not see each other's intermediate results
- •Durability: committed updates are never lost
The DBMS provides durability with the log and backups: after a system failure it rolls committed work forward from the log, and after a media failure it restores a backup and reapplies the logged updates.
Answer (c)
Why not others:
- •(a) Atomicity — concerns undoing an unfinished transaction, not keeping a committed one
- •(b) Consistency — concerns the rules the data must obey, not surviving a failure
- •(d) Isolation — concerns transactions running at the same time interfering with each other
Key rule: Durability is about committed data surviving failures; atomicity is about uncommitted work leaving no trace.
Databases · AI-written, may contain errors
This question comes from an official ITPEC past paper. ITPEC Practice is an independent study tool and is not affiliated with ITPEC. See the official FE past-paper collection or Report an issue.