Option A
Thomas Write Rule:
Transaction Ti issues a Read then below condition should be checked.
If (TS(Ti) < WTS(Q)), Ti would read a value of Q that was already overwritten by a newer transaction Tj <> Ti . Hence, this read is rejected and Ti will be rolled back.
If TS(Ti) ≥ WTS(Q), the read is approved, and we set RTS(Q) := max{RTS(Q),TS(Ti)}Data item A.
Transaction Ti issues a Write then below condition should be checked.
If(RTS(Q)>TS(Ti)) THEN rollback.
If(TS(Ti) < WTS(Q)) THEN Ignore the write and continue the transaction else
Initially RTS =0, WTS=0 For all Data Items.
1. Read request by Transaction T1 R(A), after applying above condition seems to be true,
then RTS=1,WTS=0
2. Read request by Transaction T1 R(B), after applying above conditions seems to be true,
then RTS=1,WTS=0
3. Read request by Transaction T1 R(C), after applying above conditions seems to be true,
then RTS=1,WTS=0
4. Again Read request by Transaction T2 R(A)
RTS =1,WTS=0 ,when read done by transaction T1 ,RTS and WTS updated
after applying the condition for Read request made by Transaction T2,
then RTS = 2 ,WTS=0 updated.
5. Again Read request by Transaction T2 R(B)
RTS =1,WTS=0 ,when read done by transaction T1 ,RTS and WTS updated
after applying the condition for Read request made by Transaction T2,
then RTS = 2 ,WTS=0 updated.
6.I am choosing the Option A, W(B) request made by transaction T2,
As of now RTS =2,WTS=0, now apply the condition for write request
RTS = 2,WTS= 2 and it is successfully because the conditions seems true, So write request is been granted.
7.Write request W(C) in option A by Transaction T1,
As of now RTS=1,WTS=0 , now apply the condition
RTS = 1,WTS =1 and it seems true ,so write request is granted.
8.Read request made by Transaction T2 R(C)
As of now RTS =1, WTS=1 , now apply the condition
RTS= 2,WTS=2 and it seems to be true ,so read request is granted.
By this Option A is correct ,Similarly Check For Option B.
So W(A) write request by Transaction T2 is granted but W(A) request made by transaction T1 is not granted.
So A option.
