serializability

Question

Comments

Q finally written by ??

Answer 1

option d

as the precedence graph has a cycle T1----T2---T1 so not conflict serializable

it violates the view serializable first condition i.e T1 read(q) initially but T2 or T3 didnt read(q)

Answer 2

Option A

Its a view serializable but not conflict serializable (i assume T3 write the value last ) .

Answer 3

Clearlyit is not conflict serialisable..

For View Serialisibility we need information about final Write of Q..

If Q finally written by T3 then it is View serialisable & Sequence is T1 --> T2 --> T3 otherwise not View Serialisable (Either initial read or Final write fails)..

Answer 4

option (A) is correct

precedence graph contain cycle so it is not conflict serializable

but the same schedule is view serializable because due to presence of BLIND WRITE IN transaction  T2 ,T3.!! :)

Comments

Is the presence of blind writes alone is sufficient to check whether or not a schedule is view serializable or not..?

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i don't think it is sufficient?? but this concept should be used, if examiner asked both view serializable and conflict serializable! as in this question.. 

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Here which write(Q) occurs first from T1 and T3?