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Why may this phenomenon lead to an incorrect concurrent execution despite the use of the two-phase locking protocol?

The phantom phenomenon arises when two transaction logically conflict even though they do not lock a common data item.

This usually happens due to insertion or deletion...

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Phantom Read occurs when two same queries are executed, but the rows retrieved by the two, are different. For example, suppose transaction T1 retrieves a set of rows that satisfy some search criteria. Now, Transaction T2 generates some new rows that match the search criteria for transaction T1. If transaction T1 re-executes the statement that reads the rows, it gets a different set of rows this time.

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