Let us assume that transaction T1 has arrived before transaction T2. Consider…
2018
Let us assume that transaction T1 has arrived before transaction T2. Consider the schedule
S=r1(A); r2(B) ; w2(A); w1(B) Which of the following is true?
- A.
Allowed under basic timestamp protocol.
- B.
Not allowed under basic timestamp protocols because T1 is rolled back
- C.
Not allowed under basic timestamp protocols because T2 is rolled back
- D.
None of these
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Correct answer: B
In the Timestamp Ordering Protocol, transactions are assigned timestamps upon arrival (TS(T1) < TS(T2)). The schedule involves T2 reading B before T1 writes to it. When r2(B) executes, the read timestamp of B (RTS(B)) is updated to TS(T2). Later, when T1 attempts w1(B), the protocol checks if TS(T1) < RTS(B). Since TS(T1) is less than TS(T2), T1 violates the protocol rule for writing to a data item already read by a newer transaction. Therefore, T1 must be aborted and rolled back.
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