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In standard log-based recovery, the order of operations is
Aundo all transactions first, then redo only committed ones
Bredo only committed transactions, then undo only aborted ones
Cundo uncommitted transactions first, then redo committed ones
Dredo ALL transactions (committed and not) first, then undo uncommitted
Answer & Solution
Correct answer: D. redo ALL transactions (committed and not) first, then undo uncommitted
Redo-all-first then undo-uncommitted is simpler to implement and correct: redoing uncommitted transactions is wasted work but harmless, since they get undone right after. The alternative (skip uncommitted during redo) requires careful tracking of which transactions to skip and complicates the algorithm. Production recovery (including ARIES) uses redo-all-first.
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