Effects of shaping characteristics on the performance of nested transactions Assmaa A. El-Sayed a , Hossam S. Hassanein b, * , Mohamed E. El-Sharkawi c a Kuwait University Computing Services, P.O. Box 5969, Safat 13060, Kuwait b Department of Computing and Information Science, Queen's University, Kingston, Ont., Canada K7L 3N6 c Department of Information Systems, Faculty of Computers and Information, Cairo University, Orman, Giza, Egypt Received 14 November 2000; revised 2 February 2001; accepted 4 April 2001 Abstract The nested transaction model was introduced to satisfy the requirements of advanced database applications. Moreover, it is currently the basic transaction model for new database applications like work¯ow systems and new database systems like mobile databases and object- relational databases. Though there are several performance evaluation studies of different concurrency control mechanisms in nested transactions, the effects of transaction parameters on the overall system performance have not received any attention. In this paper, we study the effects of transactions characteristics on system performance. We developed a detailed simulation model and conducted several experiments to measure the impact of transactions characteristics on the performance. First, the effect of the number of leaves on the performance of nested transactions is investigated under different shaping parameters. Also, effects of the depth of the transaction tree on the system performance are investigated. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Nested transactions; Two-phase locking; Performance evaluation; Simulation 1. Introduction Since the mid 80's database applications have changed from the traditional record-keeping applications to more advanced and complex applications, like computer aided design CAD) systems and of®ce information systems. The nested transaction model [16], originally introduced to increase transaction reliability in distributed systems, proved to be more appropriate for these new applications. Transactions in advanced database applications are characterized by being long and complex [12,13]. The conventional ¯at transaction model cannot support all the requirements of these advanced applications [3,4,10,25]. Applications that use nested transactions are diverse and include engineering design [11], cooperative work [18,19], and computer-based publications [17]. The basic nested transaction model has been extended in Ref. [22], by allowing early release of locks, in order to meet require- ments of heterogeneous distributed applications. In addition to the numerous applications requiring the use of nested transactions, the nested transaction model and its extensions are currently the basic underlying models for several advanced database systems. The transaction models in work¯ow systems [24] and mobile databases [5,15] are nested transactions. At the data model level, transactions in the object-oriented model are nested. A method applied on an object may invoke another method constituting a hierarchy of method invocations [8]. A nested transaction is a hierarchy of subtransactions, where each subtransaction may contain other subtrans- actions, or contain the atomic database operations read and write. In other words, a nested transaction is a collection of subtransactions that are composed together to form one whole atomic unit of execution [9,16]. A nested transaction is represented as a tree, called transaction tree. In the basic nested transaction model and the basic two-phase locking [16], only leaves of the transaction tree can perform read and write operations. Each leaf subtransaction is viewed as a normal ¯at transaction in the system. The leaves are executed independently. Inner subtransactions cannot request any lock on any data item. Non-leaf subtransactions only organize the control ¯ow and determine when to invoke subtransactions. Several extensions to this basic 2PL mechanism have been proposed for a recent proposal see Ref. [20]). However, the basic 2PL mechanism for Information and Software Technology 43 2001) 579±590 0950-5849/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S0950-584901)00164-1 www.elsevier.com/locate/infsof * Corresponding author. Tel.: 11-613-533-6050; fax: 11-613-533-6513. E-mail addresses: assmaa@kuc01.kuniv.edu.kw A.A. El-Sayed), hossam@cs.queensu.ca H.S. Hassanein), mel_sharkawi@hotmail.com M.E. El-Sharkawi).