Unrepeatable reads-problems of concurrent transactions, Database Management System

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Unrepeatable reads: Assume T7 reads X twice during its implementation. If it did not update X itself it could be very disturbing to see a dissimilar value of X in its next read. But this could occur if, among the two read operations, another transaction modifies X.

T7	T8	Assumed value of X=2000
T7	T8	T7	T8
READ X		2000
	UPDATE X		3000
READ X		3000

Therefore, the inconsistent values are read and results of the transaction may be in fault.

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