Consider the following four transactions:

*Transaction T1: read_item(A); read_item(D); write_item(D);

*Transaction T2: read_item(B); write_item(B); read_item(D); write_item(D);

*Transaction T3: read_item(C); write_item(C);

*Transaction T4: read_item(D); write_item(D); read_item(A); write_item(A);

Following is a log corresponding to a particular schedule at the point of a system crash.

[start_transaction, T1]

[read_item, T1, A]

[read_item, T1, D]

[write_item, T1, D, 20, 25]

[commit, T1]

[checkpoint]

[start_transaction, T2]

[read_item, T2, B]

[write_item, T2, B, 12, 18]

[start_transaction, T4]

[read_item, T4, D]

[write_item, T4, D, 15, 25]

[start_transaction, T3]

[write_item, T3, C, 30, 40]

[read_item, T4, A]

[write_item, T4, A, 30, 20]

[commit, T4]

[read_item, T2, D]

[write_item, T2, D, 15, 25] <-System Crash

Suppose that we use the immediate update protocol with checkpointing. Specify the following:

a. Which transaction will not be involved in the recovery process and why?

b. Which transactions are rolled back?

c. Which operations in the log are redoneand why?

d. Which operations in the log are undone? List the operations in the correct order that were undone.