An optimistic concurrency control mechanism without freezing for distributed database systems

Optimistic concurrency control mechanisms have the tendency of freezing the system in order to validate a transaction at the end of the transaction´s execution phase. This paper presents an optimistic concurrency control that does not freeze the database system. According to the property of conflicting transactions, concurrency control is divided into two counterparts. While one part is exercised at the data object, which responds instantly to consistency violation, the other part is exercised by messages flowing between transactions as background tasks. The whole system need not stop during the time concurrency control is exercising, nor during the time the system is restoring its state when consistency is violated. This makes the mechanism more attractive, since a higher degree of parallelism is provided between consistency control and transaction execution. An object-based model is used to present the mechanism in a distributed database system, in which communication relies heavily on message passing.