ENHANCING THE SUCCESS RATIO OF DISTRIBUTED REAL-TIME NESTED TRANSACTIONS 1 M. Abdouli, B. Sadeg, L. Amanton and A. Berred Laboratoires LIH, LMAH, UFR des Sciences et Techniques du Havre, 25 rue P. Lebon, BP 540, 76058 Le Havre cedex, FRANCE Key words: Nested Transaction, Distributed System, Concurrency Control, RTDBS Abstract: The traditional transaction models are not suited to real-time database systems (RTDBSs). Indeed, many current applications managed by these systems necessitate a kind of transactions where some of the ACID 2 properties must be ignored or adapted. In this paper, we propose a real-time concurrency control protocol and an adaptation of the Two-Phase Commit Protocol based on the nested transaction model where a nested transaction is viewed as a collection of both essential and non-essential subtransactions: the essential subtransaction has a firm 3 deadline, and the non-essential one has a soft 4 deadline. We show through simulation results, how our protocol based on this assumption, allows better concurrency between transactions and between subtransactions of the same transaction, enhancing then the success ratio 5 and the RTDBS performances, i.e., more transactions may meet their deadlines. 1 The authors would like to thank the French Research Ministry and the University of Le Havre for their financial support (ACI No 1055 and RTT project, respectively). 2 Atomicity, Consistency, Isolation, Durability 3 A transaction is aborted as soon as it misses its deadline 4 A transaction may provide useful results after its deadline, but the Quality of Service (QoS) decreases 5 Number of transactions that meet their deadline/Total number of transactions 1 INTRODUCTION RTDBSs are generally defined as the database systems supporting time-constrained transactions. The timing constraints are usually expressed in the form of transaction deadlines. The first requirement in RTDBSs is to maintain the database consistency by enforcing the concurrency control between the active transactions. The second requirement is to satisfy the real-time constraints of the transactions in order to meet their individual deadlines. In the earlier models of traditional RTDBSs, a transaction is considered as a single flat unit of tasks [Haritsa and Ramamritham, 1997, Ramamritham, 1993], which consists of a sequence of primitive actions (e.g., read and write of data-items). If one operation of the transaction fails, then the whole work done by transaction is rolled-back. Most of the previous work [Bernstein and Goodman, 1987, Krzyzagorski and Morzy, 1995] on RTDBSs have used flat transaction as the underlying transaction model, but these approaches are not suitable to many new database applications. Some applications have changed from traditional applications to more advanced and complex applications, such as computer aided design (CAD), cooperative applications and multimedia applications. The nested transaction model, originally introduced to increase transaction reliability in distributed systems [Moss, 1986], is proved to be more appropriate for these new applications. The first nested transaction model has been proposed by Moss [Moss, 1986]. A nested transaction is considered as a hierarchy of subtransactions, and each subtransaction may contain either other subtransactions, or the atomic database operations (read or write). Furthermore, a nested transaction is 233 Abdouli M., Sadeg B., Amanton L. and Berred A. (2004). ENHANCING THE SUCCESS RATIO OF DISTRIBUTED REAL-TIME NESTED TRANSACTIONS. In Proceedings of the Sixth International Conference on Enterprise Information Systems, pages 233-240 DOI: 10.5220/0002615002330240 Copyright c  SciTePress