Abstract: In a shared database system when several transactions are executed simultaneously, the consistency of database should be maintained. The techniques to ensure this consistency are concurrency control techniques. All concurrency-control schemes are based on the serializability property. The serializability properties requires that the data is accessed in a mutually exclusive manner; that means, while one transaction is accessing a data item no other transaction can modify that data item.

In this paper we had discussed various concurrency techniques, their advantages and disadvantages and making comparison of optimistic, pessimistic and multiversion techniques. We have simulated the current environment and have analysis the performance of each of these methods.

Keywords: Concurrency, Locking, Serializability