Testing of Serializability , Serializability of Schedule, Conflict and Serializable Schedule

Testing for serializability is an essential aspect of concurrency control in a database management system (DBMS). It involves verifying that a schedule of transactions is serializable, meaning that the schedule produces the same result as if the transactions were executed sequentially, one after another.

There are two main methods for testing serializability: the precedence graph method and the transaction equivalence method. The precedence graph method constructs a graph of transactions and their conflicting operations to determine if the schedule is serializable. The transaction equivalence method compares the conflicts of each transaction in the schedule with the conflicts of a serial schedule to determine if the schedule is serializable.

A serializable schedule is a schedule that can be transformed into a serial schedule without changing the final result. In other words, the order in which transactions are executed does not affect the final result of the database.

A conflict in a schedule occurs when two transactions perform conflicting operations on the same data item. A conflicting operation is an operation that reads or writes a data item that is also being read or written by another transaction. A conflict serializable schedule is a schedule that is conflict equivalent to some serial schedule.

A serializable schedule is always conflict serializable, but not all conflict serializable schedules are serializable. For example, a schedule that contains a cycle of dependencies between transactions cannot be transformed into a serial schedule, even though it is conflict serializable.

A serializable schedule is always conflict serializable, but not all conflict serializable schedules are serializable. For example, a schedule that contains a cycle of dependencies between transactions cannot be transformed into a serial schedule, even though it is conflict serializable.

To summarize, testing for serializability involves verifying that a schedule of transactions is serializable, meaning that the schedule produces the same result as if the transactions were executed sequentially. A schedule is conflict serializable if it is conflict equivalent to some serial schedule, and a conflict serializable schedule is not necessarily serializable. Conflicts occur when two transactions perform conflicting operations on the same data item.