Question

Identify the correct option about timestamp from the following:
a) Suppose Ti issues write(Q),then it TS(Ti) >R-timestamp(Q) then write operation rejected and Ti is rolled back.
b) Suppose Ti issues write(Q),then it TS(Ti) W-timestamp(Q) then read operation rejected and Ti is rolled back.

Answer 1

Answer:

Explanation:

The timestamp ordering protocol ensures that any conflicting  read / write operations are executed in timestamp order. This is to resolve the conflict.

Suppose a transaction Ti issues a read(Q)

 1.  If TS(Ti) ≤ W-timestamp(Q), then Ti needs to read a value of Q        

      that was already overwritten. Hence, the read operation is        

      rejected, and Ti  is rolled back.

 2.  If TS(Ti) ≥ W-timestamp(Q), then the read operation is  

      executed, and R-timestamp(Q) is set to the maximum of R-

      timestamp(Q) and TS(Ti).

Suppose that transaction Ti issues write(Q).

If TS(Ti) < R-timestamp(Q), then the value of Q that Ti is producing was needed previously, and the system assumed that that value would never be produced. Hence, the write operation is rejected, and Ti is rolled back.

Otherwise, the  write operation is executed, and W-timestamp(Q) is set to TS(Ti).