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GATE CSE 2015 Set 2 | Question: 46

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Consider a simple checkpointing protocol and the following set of operations in the log.

(start, T4); (write, T4, y, 2, 3); (start, T1); (commit, T4); (write, T1, z, 5, 7);

(checkpoint);

(start, T2); (write, T2, x, 1, 9); (commit, T2); (start, T3); (write, T3, z, 7, 2); 

If a crash happens now and the system tries to recover using both undo and redo operations, what are the contents of the undo list and the redo list?

  1. Undo: T3, T1; Redo: T2
  2. Undo: T3, T1; Redo: T2, T4
  3. Undo: none; Redo: T2, T4, T3, T1
  4. Undo: T3, T1, T4; Redo: T2
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