Define the two phase locking protocol, Database Management System

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Define the Two Phase Locking Protocol

This is a protocol that is used to make sure serializability of transactions. This protocol needs that every transaction issue lock and unlock requests in two phases:

Growing Phase: A transaction may acquire locks, but may not release any lock.

Shrinking Phase: A transaction may release locks, but may not acquire any new locks. Basically, a transaction is in growing phase. The transaction obtains locks as required. Just one time the transaction releases a lock, it comes in the shrinking phase, and it can issue no more lock requests. Two-phase locking makes sure conflict serializability, but does not make sure freedom from deadlock.


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