ITPEC FE Subject A April 2026 Question 23
ITPEC FE Subject A April 2026 — Question 23 of 60
A log file records the before and after values of every update, and is used to recover the database.
Those two values support the two directions of recovery:
- •Rollback (undo) — restore the before values of a transaction that failed to commit
- •Roll-forward (redo) — reapply the after values of committed transactions lost when the system stopped
Answer (d)
Why not others:
- (a) — describes mirroring / replication, keeping a live duplicate on another disk or site
- (b) — describes a backup (dump), a whole-database copy taken periodically
- (c) — describes a checkpoint, flushing updated buffers to disk to shorten recovery
Key rule: Backup restores an old whole-database state; the log supplies the changes made since then. Recovery normally needs both — restore the backup, then roll the log forward.
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