DBMS Concurrency Control

The process of managing simultaneous operation against a database so that data integrity is maintained and operation do not interfere with each other in a multi user environment.

A database without concurrency control will be compromised due to interference between users.

Two basic approaches to concurrency control

• Pessimistic approach 

               Involving lock someone who is pessimistic think that bad things are going to happen.

• Optimistic approach

               Involving versioning

Concurrency Control Action

The actions that must be taken to ensure that data integrity is maintained are called concurrency control action.

Lost update

Multiple users attempt to update a database without adequate concurrency control called lost update.

Locking mechanism are the most common type of concurrency control mechanism.

Purpose of concurrency control

• To enforce isolation ( isolation means -one transaction is not interleaving with another transaction)
• To preserve database consistency
• To resolve read-write and write-write conflicts 

Concurrency Control Techniques 

• Lock based protocol
• Timestamp methods
• Optimistic methods