Concurrency Control Mechanism
What is Concurrency Control?
Pessimistic Concurrency Control
Lock-Based Protocols
Pitfalls of Lock-Based Protocols
The Two-Phase Locking Protocol
Lock Conversions
Automatic Acquisition of Locks
Implementation of Locking
Lock Table

The Two-Phase Locking Protocol

Two-phase locking does not ensure freedom from deadlocks
Cascading roll-back is possible under two-phase locking. To avoid this, follow a modified protocol called strict two-phase locking. Here a transaction must hold all its exclusive locks till it commits/aborts.
Rigorous two-phase locking is even stricter: here all locks are held till commit/abort. In this protocol transactions can be serialized in the order in which they commit.