What does the write-ahead logging (WAL) rule require?
Correct answer B. Log records describing a change must reach stable storage before the changed data page does
Explanation
Under WAL, a modified data page may be written to disk only after the log records describing that modification have been flushed. Then, after a crash, the log always holds enough information to undo or redo any change found on disk. The first option reverses the rule. Writing all data pages at commit is the FORCE policy, which WAL lets the DBMS avoid.
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