#DBMS #View Serializability

Question

Suppose a schedule is not conflict serializable but has blind writes, only this condition is sufficient to declare the schedule as view serializable or we have to manually check for view serializability???

Answer 1

Consider the schedule:

T1        T2

---------------------

R(A)

         W(A)

W(A)

 

Now, T2 is performing blind write. But the dependencies are follows to check for view serializability:

1)  T1->T2     for the W(A) operation of T2 after the initial R(A) operation of T1.

2)  T2->T1     for the final W(A) operation of T1 after the W(A) operation of T2.

Now, we have a cycle and hence, not view seriazable.

Answer 2

Having blind writes is not sufficient condition to declare View Serializability. We need to draw polygraph and check if there are'nt any cycles in the polygraph, then only we can declare its View Serializable.

Comments

Can you tell how to draw polygraphs.??