Q5 /20 Choose the correct description of database rollforward processing.
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Choose the correct description of database rollforward processing.
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Answer: B. Restore using a journal file after updating against a physical failure.
Rollforward processing is a recovery technique used after a physical failure (like a system crash or disk failure) to restore the database to a consistent state. It involves restoring a backup copy of the database and then reapplying all committed transactions recorded in the journal file that occurred after the backup was taken, effectively replaying the updates. This is distinct from rollback, which undoes uncommitted transactions, and it applies specifically to physical failures, not logical ones.
Step-by-step Derivation:
Rollforward recovery process:
- Identify the recovery scenario: Physical failure (hardware crash, media failure) vs. Logical failure (incorrect update, data corruption)
- Rollforward is used for PHYSICAL failures, not logical ones → eliminates options C and D
- Rollforward timing: It occurs AFTER the physical failure is detected and a backup is restored, then the journal file is used to replay committed transactions → eliminates option A
- Correct sequence: Backup restored → Journal file applied (after the failure point) → Database restored to pre-failure state with all committed transactions
- Answer: B (after updating against a physical failure)