Question 8225 – Transactions
January 4, 2024Question 8165 – GATE 2015 [Set-1]
January 4, 2024Question 8263 – Transactions
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 13 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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