Concurrency Control for Time-constrained Transactions in Distributed Databases Systems

The design of concurrency control protocols for time-constrained transactions is complicated due to the requirements to maintain the database consistency and to satisfy the timing constraints of the transactions. In the past few years, various real-time locking protocols have been proposed for different real-time database systems (RTDBS). However, the use of these protocols for distributed real-time database systems (DRTDBS) has received much less attention, even though many RTDBS are distributed in nature. In this paper, two efficient real-time locking protocols are proposed for DRTDBS. The first one, based on dynamic locking, is called Distributed Hybrid Two Phase Locking (DHb2PL). Its performance has been compared in detail with three other distributed real-time locking protocols. The performance results indicate that DHb2PL is much better than the other protocols as a result of a better approach to resolving lock conflicts and its deadlock free property. The second one, called DRT-S2PL, is based on static locking where the locks required by a transaction are assumed to be known before its execution. Its relative performance as compared with DHb2PL is dependent on the proportion of remote locks required by a transaction. DRT-S2PL is more suitable for systems with transactions which have to set a large proportion of remote locks.