(i) Write down the system log for the following schedule. The symbol ci stands for commit event of the ith transaction.

r2(X); r1(Z); r3(X); w3(X); c3; w2(X); c2; w1(Z); c1; [4 Marks]

(ii) The figure below shows the log corresponding to a particular schedule at the point of a system crash for four transactions T1, T2, T3, and T4. Suppose that we use the deferred update protocol with check pointing. Describe the recovery process from the system crash. Specify which transactions are rolled back, which operations in the log are redone and which (if any) are undone. [6 Marks]

[start_transaction, T4]

[read_item, T4, D]

[read_item, T4, B]

[checkpoint]

[write_item, T4, B, 400, 800]

[commit, T4]

[start_transaction, T3]

[read_item, T3, C]

[write_item, T3, C, 700, 1000]

[start_transaction, T2]

[read_item, T2, B]

[write_item, T2, B, 800, 1600]

[start_transaction, T1]

[write_item, T1, A, 5500, 6000]

[read_item, T2, D]

[write_item, T2, D, 890, 600]

[commit, T4]

[read_item, T3, B]

[write_item, T3, B, 1600, 2000] <-- System crash