Question 14145 – Database-Management-System
March 26, 2024Question 5086 – Communication
March 26, 2024Question 14082 – Database-Management-System
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?
Correct Answer: A
Question 862 Explanation:
As T1 & T3 are not yet committed they must be undone. The transactions which are after the latest checkpoint must be redone. So T2 must be redone. No need to redo the records which are before the last checkpoint, so T4 need not be redone.
Undo : T3, T1; Redo T2
Undo : T3, T1; Redo T2, T4
Undo : none; Redo T2, T4, T3 T1
Undo : T3, T1, T4; Redo T2
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