Important properties of two phase locking protocol and its variants

Important properties of two phase locking protocol and its variants

Properties of   2PL

• Serializability 
• 2PL ensures conflict serializability.

• Growing phase
• All the data items must be locked with the required locks (either read lock or write lock) well before accessing those data items. [called Growing phase]
• Upgrading of locks can only be done during Growing phase.

• Shrinking phase
• Once the lock is released, the transaction cannot get any new locks during the execution of that particular transaction. [called Shrinking phase].
• Downgrading of locks can only be done during Shrinking phase.

• Lock point
• The end of growing phase (acquiring the final lock of a transaction) is called lock point.

• Deadlock
• 2PL does not guarantee freedom from deadlock. Deadlock may happen under two phase locking.

• Cascading rollback
• Cascading rollback may occur under 2PL.

• Variants of 2PL
• strict 2PL and rigorous 2PL.

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properties of two phase locking protocol page

important 2PL properties

facts about two phase locking protocol

simple, strict, and rigorous two phase locking protocol

upgrading and downgrading properties in 2pl

growing and shrinking phases in 2pl