A Concurrency Control Method Based on Commitment Ordering in Mobile Databases

Disconnection of mobile clients from server, in an unclear time and for an unknown duration, due to mobility of mobile clients, is the most important challenges for concurrency control in mobile database with client-server model. Applying pessimistic common classic methods of concurrency control (like 2pl) in mobile database leads to long duration blocking and increasing waiting time of transactions. Because of high rate of aborting transactions, optimistic methods aren`t appropriate in mobile database. In this article, OPCOT concurrency control algorithm is introduced based on optimistic concurrency control method. Reducing communications between mobile client and server, decreasing blocking rate and deadlock of transactions, and increasing concurrency degree are the most important motivation of using optimistic method as the basis method of OPCOT algorithm. To reduce abortion rate of transactions, in execution time of transactions` operators a timestamp is assigned to them. In other to checking commitment ordering property of scheduler, the assigned timestamp is used in server on time of commitment. In this article, serializability of OPCOT algorithm scheduler has been proved by using serializability graph. Results of evaluating simulation show that OPCOT algorithm decreases abortion rate and waiting time of transactions in compare to 2pl and optimistic algorithms.Comment: 15 pages, 13 figures, Journal: International Journal of Database Management Systems (IJDMS

An Efficient Concurrency Control Technique for Mobile Database Environment

Day by day wireless networking technology and mobile computing devices are becoming more popular for their mobility as well as great functionality Now it is an extremely growing demand to process mobile transactions in mobile databases that allow mobile users to access and operate data anytime and anywhere irrespective of their physical positions Information is shared among multiple clients and can be modified by each client independently However for the assurance of timely access and correct results in concurrent mobile transactions concurrency control techniques CCT happen to be very difficult Due to the properties of Mobile databases e g inadequate bandwidth small processing capability unreliable communication mobility etc existing mobile database CCTs cannot employ effectively With the client-server model applying common classic pessimistic techniques of concurrency control like 2PL in mobile database leads to long duration Blocking and increasing waiting time of transactions Because of high rate of aborting transactions optimistic techniques aren t appropriate in mobile database as well This paper discusses the issues that need to be addressed when designing a CCT technique for Mobile databases analyses the existing scheme of CCT and justify their performance limitations A modified optimistic concurrency control scheme is proposed which is based on the number of data items cached amount of execution time and current load of the database server Experimental results show performance benefits such as increase in average response time and decrease in waiting time of the transaction

Mobile Databases: a Selection of Open Issues and Research Directions

International audienceThis paper reports on the main results of a specific action on mobile databases conducted by CNRS in France from October 2001 to December 2002. The objective of this action was to review the state of progress in mobile databases and identify major research directions for the French database community. Rather than provide a survey of all important issues in mobile databases, this paper gives an outline of the directions in which the action participants are now engaged, namely: copy synchronization in disconnected computing, mobile transactions, database embedded in ultra-light devices, data confidentiality, P2P dissemination models and middleware adaptability

Single Phase Reliable Timeout Based Commit Protocol

The enormous progress in applications of distributeddatabase systems necessitates formulation of an efficient atomiccommitment protocol. The efficiency of these protocols is vitalwhen higher transaction throughput is to be supported. Theexisting blocking commit protocols affect over the capacity ofsystem resources, which worsens in distributed database system.This paper proposes the Non Blocking Single Phase ReliableTimeout Based Commit Protocol (SPRTBCP), an extension to theModified Reliable Timeout Based Commit Protocol (MRTBCP ),maintains the atomicity and supports off -line executions anddisconnections during commitment; it decreases the cost ofwireless communication by reducing it to a single phasecommitment operation and does not maintain log agent. Hence itreduces message complexity and average commit time . It alsosupports disconnections and handoff in mobile environment

Performances de protocoles transactionnels en environnement mobile

National audience. L'omniprésence d'unités mobiles et le développement des réseaux sans fil motivent des avancées en matière de supports d'exécution pour une grande variété d'applications en envi-ronnement mobile. Des efforts importants sont faits pour offrir une bonne gestion des données malgré les caractéristiques limitées de tels environnements. La notion de transaction a été ré-étudiée pour proposer des modèles et des protocoles permettant d'assurer certaines propriétés transactionnelles. Les algorithmes et protocoles proposés tentent d'optimiser l'utilisation des ressources des unités mobiles et de surmonter les limitations du réseau mobile. Dans cet article nous nous intéressons spécifiquement aux protocoles de validation de transactions réparties sur plusieurs unités dont certaines mobiles. Nous présentons ici les résultats d'un travail qui iden-tifie des propriétés qualitatives et des indices de performance quantitatifs, et étudie ceux-ci sur quatre protocoles (2PC, UCM, CO2PC et TCOT). Trois de ces protocoles sont des propositions spécifiques pour des environnements mobiles et sont représentatifs des propositions actuelles. Nous nous intéressons à la phase de validation des transactions, ainsi qu'à l'influence des dif-férents protocoles sur les performances du déroulement de l'ensemble des transactions. ABSTRACT. This is an abstract. The omnipresence of mobile devices and wireless networks lead to a growing interest in supporting a wide variety of applications in mobile environments. Numerous efforts in providing appropriate data managements for such environments are made. Transaction supports have been revisited to propose adapted transaction models and properties. Proposed algorithms and protocols try to optimise the use of mobile units resources and to overcome wireless network limitations. This work concerns protocols to commit transactions distributed over several mobile and fixed units. Results presented here concern the identification of qualitative properties and quantitative performance indices that are studied on four protocols (2PC, UCM, CO2PC et TCOT). Three of them are specifics propositions for mobile environments and are representative of current proposals. The analysis concerns the transaction validation phase as well as the impact of the protocols on the performances during a transaction execution itself. MOTS-CLÉS : transactions mobiles , evaluation de performances, protocoles de validation

An Efficient Concurrency Control Technique for Mobile Database Environment

Day by day, wireless networking technology and mobile computing devices are becoming more popular for their mobility as well as great functionality. Now it is an extremely growing demand to process mobile transactions in mobile databases that allow mobile users to access and operate data anytime and anywhere, irrespective of their physical positions. Information is shared among multiple clients and can be modified by each client independently. However, for the assurance of timely access and correct results in concurrent mobile transactions, concurrency control techniques (CCT) happen to be very difficult. Due to the properties of Mobile databases e.g. inadequate bandwidth, small processing capability, unreliable communication, mobility etc. existing mobile database CCTs cannot employ effectively. With the client-server model, applying common classic pessimistic techniques of concurrency control (like 2PL) in mobile database leads to long duration Blocking and increasing waiting time of transactions. Because of high rate of aborting transactions, optimistic techniques aren`t appropriate in mobile database as well. This paper discusses the issues that need to be addressed when designing a CCT technique for Mobile databases, analyses the existing scheme of CCT and justify their performance limitations. A modified optimistic concurrency control scheme is proposed which is based on the number of data items cached, amount of execution time and current load of the database server. Experimental results show performance benefits, such as increase in average response time and decrease in waiting time of the transactions

Adaptable Mobile Transactions and Environment Awareness

National audienceMobile environments are characterized by high variability (e.g. variable bandwidth, disconnections, different communication prices) as well as by limited mobile host resources. Such characteristics lead to high rates of transaction failures and unpredictable execution costs. This paper introduces an Adaptable Mobile Transaction model (AMT) that allows defining transactions with several execution alternatives associated to a particular context. The principal goal is to adapt transaction execution to context variations. An analytical study shows that using AMTs increases commit probabilities and that it is possible to choose the way transactions will be executed according to their costs. In addition, the middleware TransMobi is proposed. It manages environment awareness and implements the AMT model with suitable protocols.Les environnements mobiles sont caractérisés par une grande variabilité (bande passante variable, déconnexions, prix de communication différents, etc.) ainsi que par des uni-tés mobiles à ressources limitées. Ces caractéristiques entraînent un nombre important de défaillances transactionnels et des coûts d'exécution imprévus. Cet article introduit un modèle de transactions mobiles adaptables (AMT) permettant de définir des transactions avec plusieurs alternatives d'exécution. Le principal objectif est d'adapter l'exécution des transactions aux variations du contexte. Une étude analytique montre que les AMT augmentent la probabilité de validation et qu'il est possible de choisir le type d'exécution en fonction de son coût. Nous proposons également l'intergiciel TransMobi gérant la perception de l'environnement et implantant le modèle AMT à l'aide de protocoles appropriés