Consider the following protocol for concurrency control. The database system assigns each transaction a unique and strictly increasingly id at the start of the transaction. For each data item, the database system also keeps the id of the last transaction that has modified the data item, called the transaction-id of the data item. Before a transaction T wants to read or write on a data item A, the database system checks whether the transaction-id of A is greater than the id of T . If this is the case, the database system allows T to read/write A. Otherwise, the database system aborts and restarts T.

Question1:

Does this protocol allow only a serializable schedule for transactions? If not, you may suggest a change to the protocol so that all schedules permitted by this protocol are serializable. You should justify your answer.

Question 2:

Propose a change to this protocol or the modified version you have designed for part (a) that increases its degree of concurrency, i. e., it allows more serializable schedules.