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timestamps

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Operation X Y Z Result R W R W R W R2(Z) Reads R2(Y) Reads W2(Y) Writes R3(Y) Reads R3(Z) Reads R1(X) Reads W1(X) Writes W3(Y) Writes W3(Z) Writes R2(X) Reads R1(Y) REJECT Fill in the timestamps in the above table to show why R1(X) fails. Reject conditions: For Read(X) in Ti: Reject if TS(Ti) < write_TS(X) For Write(X) in Ti: Reject if TS(Ti) < read_TS(X) Assume TS (Ti) = i

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Operation X Y Z Result R W R W R W R2(Z) 2 Reads R2(Y) 2 Reads W2(Y) 2 2 Writes R3(Y) 3 Reads R3(Z) 3 Reads R1(X) 1 Reads W1(X) 1 Writes W3(Y) 3 Writes W3(Z) 3 Writes R2(X) 2 Reads R1(Y) REJECT Reject because 1< write_TS (Y) (equal to 3)
R3(Y) R3(Z) R1(X) W1(X) W3(Y) W3(Z) R2(Z) R1(Y) W1(Y) R2(Y) W2(Y) R2(X) W2(X) a) Is the above schedule serializable? If yes (or no), draw a precedence graph to explain your answer. If yes, what is the serialization order? b) If it is serializable, is it accepted by the timestamp protocol?

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Unformatted text preview: Prove your answer by showing the read and write timestamps of each variable during transaction execution. c) If it is serializable, is it accepted by the 2PL protocol? Prove your answer by showing where lock and unlock statements should be inserted. T 1 T 2 T 3 < T 1 < T 2 X, Y T 3 Y Y, Z Not allowed in TS (Obvious by serialization order of T3 < T1 < T2) Operation X Y Z R W R W R W R3(Y) 3 R3(Z) 3 R1(X) 1 W1(X) 1 W3(Y) 3 W3(Z) 3 R2(Z) Rejected Accepted by 2PL T1 T2 T3 LX(Y) LX(Z) R(Y) R(Z) LX(X) R(X) W(X) W(Y) W(Z) UN(Y)(unlock) UN(Z)(unlock) LS(Z) R(Z) LX(Y) R(Y) W(Y) UN(Y)(unlock) UN(X)(unlock) LX(Y) R(Y) W(Y) LX(X) R(X) W(X) UN(Y)(unlock) UN(X)(unlock) UN(Z)(unlock)...
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