DBMS · Question 10 · Medium
Which rule does Write-Ahead Logging (WAL) enforce?
- The log record for a change must reach stable storage before the modified data page is written to disk
- The modified data page must be written to disk before its log record
- Log records are written only after all data pages of the transaction are on disk
- Log records are kept only in main memory until the next checkpoint
Answer and explanation
Answer: A. The log record for a change must reach stable storage before the modified data page is written to disk
Explanation: Under WAL, the undo/redo information has to be in the stable log before the corresponding data block is written. That way, recovery after a crash can always undo or redo the change.
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