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In the following T1 and T2 are transaction and A is an object ,which of the following  has the potential of becoming of irrecoverable schedules?

A)  T2 writes A after T1 wrote A; T1 is uncommitted

B) T2 reads A after T1 wrote A;  T1 is uncommitted

C )  T2 writes A after T1 wrote A; T1 is committed

D)   T2 reads A after T1 read A; T1 is uncommitted
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B must be the answer.

Irrecoverability is when a committed transaction has to be rolled back .

A cannot be the answer , since T2 is writing A irrespective of the changes made by T1(This is called Blind Write).

B has to be the answer , since T2 is reading what T1 wrote and T1 is not committed till now . So there's a potential chance that T2 would be needed to rollback if T1 failed , to maintain consistency.

C cannot be answer since transaction is committed and D cannot be answer since Read Read are not conflicting opertations

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