An Agent Based Transaction Manager for Multidatabase Systems

A multidatabase system (MDBMS) is a facility that allows users to access data located in multiple autonomous database management systems (DBMSs) at different sites. To ensure global atomicity for multidatabase transactions, a reliable global atomic commitment protocol is a possible solution. In this protocol a centralized transaction manager (TM) receives global transactions, submits subtransactions to the appropriate sites via AGENTS. An AGENT is a component of MDBS that runs on each site; AGENTS after receiving subtransactions from the transaction manager perform the transaction and send the results back to TM. We have presented a unique proof-of-concept, a JAVA application for an Agent Based Transaction Manager that preserves global atomicity. It provides a user friendly interface through which reliable atomic commitment protocol for global transaction execution in multidatabase environment can be visualized. We demonstrated with three different test case scenarios how the protocol works. This is useful in further research in this area where atomicity of transactions can be verified for protocol correctness

Transaction execution in multidatabase systems

Ankara : Department of Computer Engineering and Information Science and Institute of Engineering and Science, Bilkent Univ., 1996.Thesis (Master's) -- Bilkent University, 1996.Includes bibliographical references leaves 80-82.Most work in the multiclatabase systems (MDBSs) area has focused on the issues of transaction management and concurrency control. It is difficult to implement traditional transaction management techniques in a MDBS due to the heterogeneity and autonomy of the connected local sites. In this thesis, we present a new transaction execution model that captures the formalism and semantics of various extended transaction models and adopts them to a MDBS environment. The proposed model covers nested transactions, various dejjendenc}' types among subtransactions, and commit-independent transactions. The execution model does not make any assumption regarding the concurrency control protocols executed at the local sites connected to the MDBS. VVe also present a detailed simulation model of a MDBS to aiiiilyze the performance of the proposed model. The performances of both the traditional transaction model and the proposed transaction model are evaluated under a range of workloads and system configurations. The performance impact of global transactions’ behavior on local transactions is also discussed.Devirmiş, TimuçinM.S

Rigorous Design of Distributed Transactions

Database replication is traditionally envisaged as a way of increasing fault-tolerance and availability. It is advantageous to replicate the data when transaction workload is predominantly read-only. However, updating replicated data within a transactional framework is a complex affair due to failures and race conditions among conflicting transactions. This thesis investigates various mechanisms for the management of replicas in a large distributed system, formalizing and reasoning about the behavior of such systems using Event-B. We begin by studying current approaches for the management of replicated data and explore the use of broadcast primitives for processing transactions. Subsequently, we outline how a refinement based approach can be used for the development of a reliable replicated database system that ensures atomic commitment of distributed transactions using ordered broadcasts. Event-B is a formal technique that consists of describing rigorously the problem in an abstract model, introducing solutions or design details in refinement steps to obtain more concrete specifications, and verifying that the proposed solutions are correct. This technique requires the discharge of proof obligations for consistency checking and refinement checking. The B tools provide significant automated proof support for generation of the proof obligations and discharging them. The majority of the proof obligations are proved by the automatic prover of the tools. However, some complex proof obligations require interaction with the interactive prover. These proof obligations also help discover new system invariants. The proof obligations and the invariants help us to understand the complexity of the problem and the correctness of the solutions. They also provide a clear insight into the system and enhance our understanding of why a design decision should work. The objective of the research is to demonstrate a technique for the incremental construction of formal models of distributed systems and reasoning about them, to develop the technique for the discovery of gluing invariants due to prover failure to automatically discharge a proof obligation and to develop guidelines for verification of distributed algorithms using the technique of abstraction and refinement

Priority-based speculative locking protocols for distributed real-time database systems.

With globalization, multinational networked organizations' need for exchange of information has led to the emergence of applications that are heavily dependent on globally distributed and constantly changing data. Such applications include, stock trading, Computer Aided Design and Manufacturing (CAD/CAM), online reservation systems, telecommunication systems, e-commerce systems and real time navigation systems. These applications introduce the need for distributed real time database systems (DRTDBS) which must access/manipulate data spread over a network in addition to meeting the real time constraints and maintaining database consistency. In order to improve performance within DRTDBS, attention needs to be given to concurrency control mechanism and transaction's time constraints. A number of protocols have been suggested in recent years to address these issues. One of the proposed protocols, Speculative Locking (SL), has especially demonstrated the capability of improving performance within Distributed Database System by allowing parallelism between conflicting transactions without violating serializability. This research extends SL by giving it the capability of taking a transaction's priority into consideration when scheduling transactions. In addition, a nested transaction model is used to access the data that is distributed across the network. We propose two new Priority-based Speculative Locking protocols: (1) Preemptive Speculative Locking (PSL) and (2) Priority inheritance Speculative Locking (PiSL). PSL extends SL by allowing any incoming higher priority transaction to preempt and abort any lower priority transaction in case of lock conflict thus giving the higher priority transaction a chance to meet the deadline. PiSL, on the other hand, attempts to prevent any wasted work by avoiding preemption by a higher priority transaction. Instead, the lower priority transaction inherits the priority of the blocked transaction. This gives both transactions an opportunity to meet their deadline whenever possible.The original print copy of this thesis may be available here: http://wizard.unbc.ca/record=b159863

Mobile Datenbanken - heute, morgen und in 20 Jahren. Tagungsband zum 8. Workshop des GI-Arbeitskreises "Mobile Datenbanken und Informationssysteme" am 28.2.2005 im Rahmen der BTW 2005 in Karlsruhe

Der Workshop Mobile Datenbanken heute, morgen und in 20 Jahren ist der nunmehr achte Workshop des GI Arbeitskreises Mobile Datenbanken und Informationssysteme. Der Workshop findet im Rahmen der BTW 2005, der GI Fachtagung für Datenbanksysteme in Business, Technologie und Web, vom 28. Februar bis zum 01. März 2005 in Karlsruhe statt. Das Workshopprogramm umfasst zwei eingeladene Vorträge sowie sieben wissenschaftliche Beiträge, die vom Programmkomitee aus den Einreichungen ausgewählt wurden. Für den zweiten Workshoptag, der im Zeichen intensiver Diskussionen stehen soll, wurden zwei weitere Einreichungen als Diskussionsgrundlage ausgewählt. Inhaltlich spannt der Workshop einen weiten Bogen: Von fast schon klassischen Fragen aus dem Kernbereich mobiler Datenbanken, wie etwa der Transaktionsbearbeitung in diesen Systemen, bis hin zu neuen Multimediaanwendungen auf mobilen Geräten und von der Anfragebearbeitung in Ad-hoc-Netzen bis zur Analyse des Stands der Technik beim Entwurf mobiler Anwendungen. Diese Breite spiegelt die Breite der Fragestellungen, die bei der Betrachtung von mobiler Informationsnutzung zu Tage treten, wider. Wir hoffen mit unserem Workshop einen Beitrag zum besseren Verständnis dieser Fragestellungen zu liefern und ein Forum zum Austausch von Fragen, Lösungsansätzen und Problemstellungen zwischen Praktikern und Forschern aus dem universitären Umfeld zu bieten

Transaction management for mobile objects using optimistic concurrency control

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1994.Includes bibliographical references (p. 89-93).by Atul Adya.M.S