Discuss how serializability is used to enforce concurrency control in a database system. Why is serializability sometimes considered too restrictive as a measure of correctness for schedules?

Start with the concept of serializability. It is a property of database transactions that ensures consistent behavior when multiple transactions are executed concurrently. Serializability ensures that the outcome of executing a set of transactions concurrently is equivalent to some execution where transactions are executed serially (one after the other). By enforcing serializability, database systems can control the concurrent execution of transactions and maintain consistency.

Now, it is time to explain how serializability enforces concurrency control in a database system. Serializability allows multiple transactions to be in process at the same time and still ensures data consistency. It controls the interleaving of instructions from different transactions in such a way that the end result is the same as if the transactions were executed one at a time, or serially. This prevents data inconsistency that might arise when transactions execute in an unrestricted manner.

Finally, discuss why serializability is sometimes seen as too restrictive for schedules. While serializability is crucial for maintaining data consistency, it might not be necessary or even desirable for all types of database operations. For example, there might be situations where certain interleavings of transactions could improve system performance without compromising data correctness. This is because serializability checks for all possible conflicts between transactions, although some conflicts might not actually affect the final state of the database. Hence, there may be schedules classified as non-serializable which are still correct. In such cases, enforcing serializability may limit the level of concurrency and affect system performance.