Transaction Recovery After Rollback: Commit vs Rollback vs Flashback vs Redo

In database systems, rollback undoes the effects of a transaction that has not been committed (or reverts changes within the scope of a failed/aborted operation), while redo is part of the recovery process used to re-apply changes after a failure (e.g., during crash recovery). Flashback features allow you to view or revert to a prior state using specialized mechanisms rather than a traditional rollback. Commit finalizes a transaction so its changes become durable and are not undone by rollback.

For the question: “Which of the following is used to get back all the transactions back after rollback?” the best answer among the options is (iv) Redo, because redo is used to restore/re-apply changes during recovery so that the system returns to the correct state after undo/rollback-type steps in the recovery workflow.

Key terms introduced next: Rollback Redo Flashback Commit.

Conceptual recovery model (Undo vs Redo)

Many recovery approaches can be understood as separating “undoing wrong/unwanted effects” from “re-applying correct effects.” In that mental model:

• Rollback/Undo addresses the effects of transactions that should not remain (e.g., aborted work).
• Redo ensures the effects that must persist (e.g., committed work, or changes recorded in logs) are re-applied to reach the correct database state after failure.

This aligns with how exam questions usually test transaction recovery: after rollback/undo, the mechanism that “gets back” the intended history is redo.