At the time of a system crash, let the log segment (in the undo/redo logging scheme) be as follows:
(START S);
(S, X, 10, 20);
(COMMIT S);
(START T);
(T, X, 20, 30);
(START CKPT(T));
(T, Y, 10, 20);
(START U);
(COMMIT T);
(U, X, 30, 40);
(END CKPT);
(U, Y, 20, 30);
(START V);
(START CKPT(U,V));
(COMMIT U);
(V, Y, 30, 40)
Assume that there has been a system crash, and recovery is about to begin based on the log given to you. Return all the possible values of X and Y after the system crash but before the recovery started. You are required to submit detailed explanations of your solution.