A Hybrid Approach for Improving Concurrency of Frequently Disconnecting Transactions

Transaction management in different contexts, such as a mobile environment, is still a challenging task. In this paper we propose an efficient integrated method in order to improve concurrency of long lived transactions. Differently from other techniques presented in the literature, we design a hybrid approach between optimistic and pessimistic models. From one hand, our basic idea consists in the modification of the well known 2PL protocol, in order to take into account frequent disconnections or inactivity periods of mobile devices and, from the other one, we consider the semantic related to operations produced by transactions. The first condition is necessary in order to avoid an indefinite or long resource locking, by disconnecting (or idle) transactions or a high rate of preventive aborts; in the opposite, a transaction "semantic compatibility" is exploited in order to increase the concurrency of reconcilable operations on the same resources. We have implemented a middleware with the aims of emulating a classical transactional scheduler, and several experiments have been carried out.