In a database management system (DBMS), a serializable schedule is a way of executing concurrent transactions in a way that produces the same result as if the transactions were executed serially (one after the other). In other words, a serializable schedule ensures that the concurrent execution of transactions preserves the integrity of the database, as if the transactions were executed one at a time.
A serializable schedule is achieved through the use of locks, which are used to prevent multiple transactions from accessing and modifying the same data simultaneously. When a transaction acquires a lock on a piece of data, no other transaction can access or modify that data until the lock is released. This ensures that the transactions are executed in a serial fashion, even though they are running concurrently.
Here is an example of how a serializable schedule might work in a DBMS:
- Transaction 1 begins and acquires a lock on data D.
- Transaction 2 begins and tries to acquire a lock on data D, but is blocked because Transaction 1 has a lock on D.
- Transaction 1 completes and releases the lock on D.
- Transaction 2 acquires the lock on D and begins executing.
In this example, Transaction 2 is executed after Transaction 1, even though they were running concurrently. This ensures that the integrity of the database is preserved, as if the transactions were executed one at a time.