Suppose when a crash occurred, the log in the stable storage has the following records in the given order (where T1, T2 and T3 represent different transactions):
,,,,,,,,
(a) If the deferred database modification recovery technique is used, what should be done to T1, T2 and T3 (the choices are "no action", "redo" and "undo")? Before the crash, what are the values of A, B, and D as can be seen by other database users with access privilege? After the recovery is completed, what are the values of A,B and D in the database? (b) If the immediate database modification recovery technique is used and the real database is updated as soon as possible (assume that for all log records in the stable storage, the corresponding changes have been made to the real database), what should be done to T1, T2 and T3? Before the crash, what are the values of A, B, and D as can be seen by other database users with access privilege? After the recovery is completed, what are the values of A,B and D in the database?
