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

  • A.Commutative
  • B.Associative
  • C.idempotent
  • D.distributive

Answer: C

Correct answer: idempotent

Recovery may be interrupted and restarted, so an undo or redo may be applied more than once to the same record. The operations are therefore written to be idempotent: applying them twice leaves the same result as applying them once.

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