A buffer manager uses the STEAL and NO-FORCE policies. Which recovery actions must the log support?
Correct answer D. Both undo and redo
Explanation
STEAL lets uncommitted changes be written to disk, so after a crash those changes must be undone. NO-FORCE lets a transaction commit before its pages are written, so committed changes may be missing and must be redone. Supporting both gives the best runtime performance at the price of more complex recovery, which is what ARIES-style systems do. NO-STEAL with FORCE would need neither.
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