ITPEC FE Morning October 2021 Question 58
In the event of a disk failure, which of the following is a method for recovering a database by restoring a full backup data onto a disk from a tape, and then reflecting, from logs, post-update copies after the full backup was taken?
Explanation
Roll forward — restore the backup, then reapply the after-images from the log up to the failure.
After a disk (media) failure the data on the disk is lost, so recovery starts from the last full backup and then reapplies, from the log, the post-update images of the transactions committed since that backup. The database returns to its state just before the failure.
Answer (c)
Why not others:
- •(a) Checkpoint restart — resumes a program or system from a checkpoint taken during processing, when the stored data is still intact; it does not restore a backup from tape.
- •(b) Reboot — restarts the system and recovers no lost data.
- •(d) Rollback — uses the before-images in the log to undo uncommitted transactions after a transaction or system failure, moving the database backward, not forward from a backup.
Key rule: A media failure needs the backup plus roll forward with after-images; a transaction or system failure with the disk intact needs rollback of uncommitted work with before-images.
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.