Suppose that we use the deferred update protocol for the example in Figure 22.6. Show how the log would be different in the case of deferred update by removing the unnecessary log entries; then describe the recovery process, using your modified log. Assume that only REDO operations are applied, and specify which operations in the log are redone and which are ignored.

Figure 22.6

[start_transaction, T;] [read_item, T,, A] [read_item, T,, D] [write_item, T,, D, 20, 25] [commit, T,] [checkpoint] [start_transaction, T3] [read_item, T2, B] [write_item, T2, B, 12, 18] [start_transaction, Ta] [read_item, T4, D] [write_item, T4, D, 25, 15] [start_transaction, T3] [write_item, T3, C, 30, 40] [read_item, T4, Al] [write_item, T4, A, 30, 20] [commit, T4) [read_item, T2, D] [write_item, T2, D, 15, 25] System crash