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Chapter 18: Problem 1

What is the two-phase locking protocol? How does it guarantee serializability?

Short Answer

Expert verified
The Two-Phase Locking Protocol is a concurrency control method that ensures database transactions are executed serially, thereby preventing data inconsistencies and conflicts. It works in two phases- the growing phase, where a transaction acquires all needed locks and the shrinking phase, where all locks are released. By maintaining the order of lock acquisition and release, it guarantees serializable schedules, meaning that the concurrent execution of transactions yields the same result as if those transactions had been executed sequentially.

Step by step solution

01

Define Two-Phase Locking Protocol

The two-phase locking protocol is a concurrency control method that ensures database transactions are executed serially, thereby preventing problems such as dirty reads, non-repeatable reads, and phantom reads.
02

Explain the Working of the Two-phase Locking Protocol

This protocol works in two distinct phases: the Growing Phase and the Shrinking Phase.\n\nThe Growing Phase is when a transaction acquires all the locks it needs, without releasing any. The transaction can obtain locks as needed, but once it releases a lock, it cannot obtain new ones.\n\nIn the Shrinking Phase, the transaction releases all its locks and can't request any new locks. Once all locks have been released, the transaction has been committed. This order of lock acquisition and release ensures that the transactions behave as if they were executed in some serial order.
03

Explain How Two-phase Locking Protocol Guarantees Serializability

Serializability means that the concurrent execution of a series of transactions yields the same result as if those transactions had been executed one after the other, in some order. The two-phase locking protocol achieves this by ensuring no two transactions overlap in a way that could produce inconsistent results. It does this by maintaining the lock on a data item until the transaction is fully completed. As a result, other transactions that may need this data item will have to wait, hence ensuring the integrity and consistency of the database, and guaranteeing serializable schedules.

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Most popular questions from this chapter

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