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# Consider schedules S1 and S2 below. S1: r1(X), r2(Y), r1(Z), w2(Y), r3(X), w1(Z), r3(Y), r2(Z), r3(Z), r1(Y),

w1(Y), w2(Z), w3(X), w3(Z) S2: r2(X), r2(Z), r3(Y), r3(X), w2(Z), r1(Y), w3(X), r1(X), w1(X), r3(Z), w3(Z), r1(Z), w1(Y), w1(Z) (a) Apply the basic timestamp ordering (BTO) algorithm to schedules S1 and S2. Determine whether or not the algorithm allows the execution of the schedules, and discuss cascading rollback (if any). Hints: each operation takes one time unit, and timestamp of each transaction is the time associated to its first operation. For example, timestamps of transactions T1, T2, and T3 in schedule S1 are 3, 7, and 1 (respectively). [20 marks] (b) Testing the serializability of S1 and S2 by serialization graph technique to prove that the successful execution of a schedule under BTO will ensure the serializability of the schedule. [15 marks] (c) Examine the recoverable characteristic of S1 and S2. What schedule (S1 or S2) can be executed under the strict timestamp ordering (STO) algorithm and write an equivalent strict schedule for it? We assume that a transaction will be be committed or aborted right after its last operation. [15 marks] (d) Examine the two-phase locking (2PL) technique on S1 and S2with an assumption of unlock operations being done as late as possible. Are BTO schedules also 2PL schedules?

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