ITPEC FE Subject A October 2024 Question 21
Source exam: ITPEC FE Subject A October 2024Topic: Databases
ITPEC FE Subject A October 2024 — Question 21 of 60
Rollback Recovery — uses pre-update log data to undo an incomplete transaction.
When a transaction fails mid-update, the DBMS performs a rollback using before-image data from the log file.
- •Pre-update (before image) — state before the change; used for rollback (undo)
- •Post-update (after image) — state after the change; used for roll-forward (redo)
- •Backup file — full database copy for disaster recovery, not single-transaction rollback
- •Snapshot — point-in-time image of the system, not used for transaction-level recovery
Key rule: Rollback = undo = pre-update log info. Roll-forward = redo = post-update log info.
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