Determining Strict 2PL

Question

Which of the following schedules are allowed by strict 2pl with shared and xclusive locks -

1. r1(A); r2(B); r3(C); w1(B); c1; w2(C); c2; w3(D); c3
2. r1(A); r2(B); r3(C); r1(B); r2(C); r3(D); c3; w1(C); c1; w2(D); c2
3. r1(A); r2(B); r3(C); w1(B); w2(C); w3(A); c1; c2; c3
4. None of the above

The solution given is 3). But how can the solution be 3) as it is not conflict serializable?

Is this the correct procedure to determine if a schedule is strict 2pl -

Check for conflict serializablility and strict recoverability and both must be satisfied.

In the above 1) and 2) satisfy conflict serializablility and strict recoverability. Then which is the correct solution?

Comments

I think ques should be which is not allowed in strict 2PL
both 1 & 2 are allowed in strict 2PL
and only 3rd is not allowed

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Answer – D.

because they are not even following basic time stamp protocol .there is conflict between growing and shrinking phase of transactions .so answer is none of the above