2. Which of the following schedules is (conflict) serializable? For each seriali

Question

2. Which of the following schedules is (conflict) serializable? For each serializable schedule, determine the equivalent serial                    schedules.                 

(a) w1 (X); r2 (X); w1(X); r3(X); w2(X)                 

(b) r1 (X); r3 (X); w2(X); w1(X); r3(X)                 

(c) w3 (X); r2 (X); w3(X); r1(X); w1(X)                 

(d) r3 (X); r1 (X); r2(X); w3(X); w2(X)                 

(e) r1(x); r2(z); w3(x); r1(z); r2(y); r3(y); r1(x); w2(z); w3(y); w2(y)                 

(15 points)                 

3. Consider schedules S1, S2, and S3 below. Determine whether each schedule is strict, cascadeless,                    recoverable, or nonrecoverable. (Determine the strictest recoverability condition that each schedule satisfies.)                 

S1: w1(x); r2(z); r1(z); w3(x); r3(y); w1(x); c1; w3(y); c3; r2(y); w2(z); w2(y);c2                 

S2: r1(x); w2(z); r1(z); r3(x); r3(y); w1(x); w3(y); w2(y); w2(z); w2(y); c1; c2; c3;                 

S3: w1(x); r2(z); r3(x); r1(z); w2(y); r3(y); w1(x); w2(z); w3(y); w2(y); c3; c2;                 

(15 points)

Explanation / Answer

(b) This schedule is not serializable because T1 reads X (r1(X)) before T3 but T3 reads X

(r3(X)) before T1 writes X (w1(X)), where X is a common data item. The operation

r2(X) of T2 does not affect the schedule at all so its position in the schedule is

irrelevant. In a serial schedule T1, T2, and T3, the operation w1(X) comes after r3(X),

2.

s2

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