GATE CS 2015 Set 3 — Question 54

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?