Check the view serializability for the given schedules(DBMS)

A schedule has view-serializability if it is viewed as equivalent to a serial schedule. A schedule is view serializable if the following three rules are satisfied −

• Rule 1 − If Ti reads data initially, after this Tj writes the same data, in the given schedule. This sequence must be followed in the transaction combination (read write operation).

• Rule 2 − If Ti writes data initially, after this Tj reads the same data, in the given schedule. This sequence must be followed in the transaction combination (write read operation).

• Rule 3 − If Ti writes data, after this Tj writes the data finally. This sequence must be followed in the transaction combination (write-write operation).

Problem

Check the view serializability for the schedules W3(X), R2(X), W2(Y), R1(Z), W3(Y), W1(Y).

Solution

We have three transactions, so the transaction combinations are as follows −

Here,

Rule 1 − T2 reads initially, after this number transaction writes the same data. So we keep all the transaction combinations.

Rule 2 − T3 writes initially, after this T1 reads the same data Z that means the transaction sequence must be “t3 followed by T1”. So remove the following combinations where “T3 is not allowed by T1”, that is T1 occurs before T3.

Rule 3 − T1 writes data finally, that means T1 must occur at last. So remove following combination where “T1 does not occur at last”

Hence, two combinations left to satisfy the view serializability are −

Conclusion

The given schedule is view serializable.