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What is Lock-based Protocol?

Lock-based protocol is a method by which any transaction cannot be read or write data until it acquires appropriate lock on database system. 

Locks are of two kinds:

1. Binary Locks: A lock on a data item can be in two states; it is either locked or unlocked.

2. Shared/exclusive Locks: This is when a lock is acquired on a data item to execute a write operation.

What is Simplistic Lock Protocol?

Simplistic lock-based protocols permit transactions to acquire a lock on every object before a 'write' operation is executed. 

What is Pre-claiming Lock Protocol?

Pre-claiming protocols estimate their operations and create a list of data items on which they need locks. Before starting an execution, the transaction requests the system for all the locks it needs beforehand. If all the locks are approved, the transaction performs and releases all the locks when all its operations are over. If all the locks are not approved, the transaction rolls back and waits until all the locks are granted.

What is Two-Phase Locking – 2pl?

This locking protocol separates the execution phase of a transaction into three parts. In the first part, when the transaction starts executing, it seeks permission for the locks it needs. The second part is where the transaction obtains all the locks. As soon as the transaction releases its first lock, the third phase starts. In this phase, the transaction cannot demand any new locks; it only releases the obtained locks.

Two-phase locking has two phases, one is growing, where all the locks are being obtained by the transaction; and the second phase is shrinking, where the locks held by the transaction are being released.
To claim an exclusive (write) lock, a transaction must first obtain a shared (read) lock and then upgrade it to an exclusive lock.

What is Strict Two-Phase Locking?

The first phase of Strict-2PL is same as 2PL. After obtaining all the locks in the first phase, the transaction continues to perform normally. But in contrast to 2PL, Strict-2PL does not release a lock after using it. Strict-2PL holds all the locks until the commit point and releases all the locks at a time.


Reference: Tutorials Point | Wikipedia

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