Optimistic Concurrency Control (OCC)

Optimistic concurrency control (OCC) is a concurrency control method that was first proposed in 1981 by Kung et al.H. T. Kung and J. T. Robinson, “On optimistic methods for concurrency control,” ACM Transactions on Database Systems, Volume 6, Issue 2, 1981., where transactions can access data items without acquiring locks on them.

In this method, transactions execute in the following three phases:

• Begin
• Read & modify
• Validate & commit/rollback

Begin phase

In this phase, transactions are assigned a unique timestampA timestamp is a monotonically increasing number, often based on the system clock. that marks the beginning of the transaction referred to as the start timestamp.

Read & modify phase

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