The lost update anomaly is said to occur if a transaction Tj reads a data item, then another transaction Tk writes the data item (possibly based on a previous read), after which Tj writes the data item. The update performed by Tk has been lost, since the update done by Tj ignored the value written by Tk.

a. Give an example of a schedule showing the lost update anomaly.

b. Give an example schedule to show that the lost update anomaly is possible with the read committed isolation level.

c. Explain why the lost update anomaly is not possible with the repeatable read isolation level.

T T4 T5 T T3