How do optimistic concurrency control techniques differ from other concurrency control techniques? Why they are also called validation or certification techniques? Discuss the typical phases of an optimistic concurrency control method.

Optimistic Concurrency Control (OCC) techniques differ from other concurrency control techniques, such as pessimistic concurrency control, in their approach to handling conflicts.

1. Approach to Handling Conflicts:

   • In pessimistic concurrency control, locks are used to prevent conflicts from occurring. This means that if a transaction wants to access a data item that is already being used by another transaction, it must wait until the other transaction releases it. This can lead to delays and inefficiencies, especially in systems with high contention.
   • On the other hand, OCC assumes that conflicts are rare and allows transactions to proceed without locks. Instead, it checks for conflicts at the end of each transaction. If a conflict is detected, the transaction is aborted and restarted.

2. Why are they called validation or certification techniques?

   • OCC techniques are also known as validation or certification techniques because they validate or certify that a transaction has not caused any conflicts before it is committed. This is done in the validation phase, where the system checks if the transaction has read any data items that were modified by other transactions that committed during its execution. If such a conflict is detected, the transaction is aborted and restarted.

3. Phases of an Optimistic Concurrency Control Method:

   • Read Phase: The transaction reads from the database without acquiring any locks. Any changes made by the transaction are made to a local copy of the database.
   • Validation Phase: The system checks if the transaction has read any data items that were modified by other transactions that committed during its execution. If such a conflict is detected, the transaction is aborted and restarted.
   • Write Phase: If the transaction passes the validation phase, it is allowed to write its changes to the database. This is done atomically to ensure consistency.

In summary, OCC techniques are more optimistic in their approach to handling conflicts, assuming that they are rare and allowing transactions to proceed without locks. They are called validation or certification techniques because they validate or certify transactions before they are committed. The typical phases of an OCC method are the read phase, validation phase, and write phase.