Consider the following schedules and find out the irrecoverable schedule:
S₁ = W₁(A)W₂(B)W₂(C)C₂R₁(A)W₁(B)C₁R₃(B)W₃(C)C₃.
S₂ = R₁(A)W₁(A)R₂(A)W₂(A)C₂C₁.
(A) S₁ is irrecoverable schedule.
(B) S₂ is irrecoverable schedule.
(C) Both are irrecoverable schedules.
(D) Both are recoverable schedule.


Answer: (B)

Explanation: S₁ = W₁(A)W₂(B)W₂(C)C₂R₁(A)W₁(B)W₂(C)C₂C₁R₃(B)W₃(C)C₃.
S₁ is recoverable since there is only one updated read which is also after other transaction got committed.
S₂ = R₁(A)W₁(A)R₂(A)W₂(A)C₂C₁.
T₂ in S₂ is reading updated value of A from T₁ and T₁ is not committed yet, T₂ must wait to commit till T₁ is not not committed
S is a recoverable schedule but it does not avoid cascaded rollback and it is not a serial schedule also.
So, option (B) is correct.

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