Explain what is meant by the constrained write rule, and explain how to test whether a schedule is serializable under the constrained write rule. Using the above method, determine whether the following schedule is serializable:
S = [R 1 (Z), R 2 (Y), W 2 (Y), R 3 (Y), R 1 (X), W 1 (X), W 1 (Z), W 3 (Y), R 2 (X), R 1 (Y), W 1 (Y),
W 2 (X), R 3 (W), W 3 (W)]
where R i (Z)/W i (Z) indicates a read/write by transaction i on data item Z.
Constrained write rule: transaction updates a data item based on its old value, which is first read
by the transaction. A precedence graph can be produced to test for serializability.
Cycle in precedence graph, which implies that schedule is not serializable.
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