For correct behaviour during recovery, undo and redo operation must be

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• If                        are not obtained in undo operation it will cause problem in undo- phase.
•                        determines which transactions to undo, which pages were dirty at the time of the crash, and the LSN from which the redo pass should start.
•                      starts from a position determined during analysis, and performs a redo, repeating history, to bring the database to a state it was in before the crash.
• A special redo-only log record < Ti, Xj, V1> is written to the log, where V1 is the value being restored to data item Xj during the rollback. These log records are sometimes called
• Once the lower-level lock is released, the operation cannot be undone by using the old values of updated data items, and must instead be undone by executing a compensating operation; such an operation is called
• Redo operations are performed exclusively using
• The recovery scheme must also provide
• During recovery from a failure
•                              is used to minimize unnecessary redos during recovery.
• In order to undo the work of transaction after last commit which one should be used?