Relative Time Correctness for Mobile Real-Time Transactions and Its Implementation

With the rapid advances in mobile computing technology, there is an increasing demand for processing real time transactions in a mobile environment. Due to the intrinsic limitation of a mobile environment, there can be a large time latency for a data accessing. Sometimes the data can even be unavailable due to the network disconnection. All these have a negative impact on the timing constraint satisfaction for a mobile real time transaction. For a mobile real time transaction, the deadline satisfaction is more important than the absolute correctness for the logical result. In this paper, a relative time correctness criterion for mobile real time transactions is proposed. As long as the staleness for the accessed data of a transaction is in a controlled scope, it is unnecessary to require that all the accessed data be valid when a mobile real time transaction commits. Then a transaction execution model is introduced together with the policy to implement the transaction relative time correctness. All these strategies reduce the concurrency control costs. Extensive experiments show that the proposed relative time correctness criterion can increase the ratio for transactions that meet their deadlines and thus the system performance is improved greatly.