69 research outputs found

    Design and evaluation of a new transaction execution model for multidatabase systems

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    Cataloged from PDF version of article.In this paper, we present a new transaction execution model that captures the formalism and semantics of various extended transaction models and adopts them to a multidatabase system (MDBS) environment. The proposed model covers nested transactions, various dependency types among transactions, and commit independent transactions. The formulation of complex MDBS transaction types can be accomplished easily with the extended semantics captured in the model. A detailed performance model of an MDBS is employed in investigating the performance implications of the proposed transaction model. © Elsevier Science Inc. 1997

    A comparative study of transaction management services in multidatabase heterogeneous systems

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    Multidatabases are being actively researched as a relatively new area in which many aspects are not yet fully understood. This area of transaction management in multidatabase systems still has many unresolved problems. The problem areas which this dissertation addresses are classification of multidatabase systems, global concurrency control, correctness criterion in a multidatabase environment, global deadlock detection, atomic commitment and crash recovery. A core group of research addressing these problems was identified and studied. The dissertation contributes to the multidatabase transaction management topic by introducing an alternative classification method for such multiple database systems; assessing existing research into transaction management schemes and based on this assessment, proposes a transaction processing model founded on the optimal properties of transaction management identified during the course of this research.ComputingM. Sc. (Computer Science

    An Agent Based Transaction Manager for Multidatabase Systems

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    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

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    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

    Concurrency Control in Multidatabases

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    Computer Science

    Transaction management in mobile multidatabases.

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    This dissertation studies transaction management in the mobile Multidatabase environment. That is, it studies the management of transactions within the context of the mobile and Multidatabase environments. Two new transaction management techniques for the mobile Multidatabase environment i.e., the PS and Semantic-PS techniques are proposed. These techniques define two now states (Disconnected and Suspended) to address the disconnectivity of the mobile user. A new Partial Global Serialization Graph algorithm is introduced to verify the isolation property of global transactions. This algorithm verifies the serializability of a global transaction by constructing a partial global serialization graph. This algorithm relies on the propagation of (serialization) information to ensure that the partial graph contains sufficient information to verify serializability of global transactions. The unfair treatment of mobile transactions due to their prolonged execution time is minimized through pre-serialization. Pre-serialization allows mobile transactions to establish their serialization order prior to completing their execution.The Internet and advances in wireless communication technology have transformed many facets of the computer environment. Virtual connectivity through the internet has lead to a new genre of software systems, i.e., cooperating autonomous systems---systems that cooperate with each other to provide extended services to the user. Multidatabase systems---a set of databases that cooperate with each other in order to provide a single logical view of the underlying information---is an example of such systems. Advances in wireless communication technology dictate that the services available to the wired user be made available to the mobile user.Finally, analytical evaluation and simulation is carried out to study the performance of these techniques and to compare their performance to that of the Kangaroo [DHB97] technique. Although the PS and Semantic-PS techniques enforce the isolation property, the evaluation results establish that the service time for these techniques in not significantly greater than that of the Kangaroo technique. In addition, the simulation establishes that pre-serialization effectively minimizes the unfair treatment of mobile transactions

    Global scheduling for flexible transactions in heterogeneous distributed database systems

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    An object query language for multimedia federations

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    The Fischlar system provides a large centralised repository of multimedia files. As expansion is difficult in centralised systems and as different user groups have a requirement to define their own schemas, the EGTV (Efficient Global Transactions for Video) project was established to examine how the distribution of this database could be managed. The federated database approach is advocated where global schema is designed in a top-down approach, while all multimedia and textual data is stored in object-oriented (O-O) and object-relational (0-R) compliant databases. This thesis investigates queries and updates on large multimedia collections organised in the database federation. The goal of this research is to provide a generic query language capable of interrogating global and local multimedia database schemas. Therefore, a new query language EQL is defined to facilitate the querying of object-oriented and objectrelational database schemas in a database and platform independent manner, and acts as a canonical language for database federations. A new canonical language was required as the existing query language standards (SQL: 1999 and OQL) axe generally incompatible and translation between them is not trivial. EQL is supported with a formally defined object algebra and specified semantics for query evaluation. The ability to capture and store metadata of multiple database schemas is essential when constructing and querying a federated schema. Therefore we also present a new platform independent metamodel for specifying multimedia schemas stored in both object-oriented and object-relational databases. This metadata information is later used for the construction of a global schemas, and during the evaluation of local and global queries. Another important feature of any federated system is the ability to unambiguously define database schemas. The schema definition language for an EGTV database federation must be capable of specifying both object-oriented and object-relational schemas in the database independent format. As XML represents a standard for encoding and distributing data across various platforms, a language based upon XML has been developed as a part of our research. The ODLx (Object Definition Language XML) language specifies a set of XMLbased structures for defining complex database schemas capable of representing different multimedia types. The language is fully integrated with the EGTV metamodel through which ODLx schemas can be mapped to 0-0 and 0-R databases

    Transaktionen in föderierten Datenbanksystemen unter eingeschränkten Isolation Levels

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    Atomarität und Isolation von Transaktionen sind Schlüsseleigenschaften fortgeschrittener Anwendungen in föderierten Systemen, die aus verteilten, heterogenen Komponenten bestehen. Während Atomarität von praktisch allen realen Systemen durch das Zweiphasen- Commitprotokoll gewährleistet wird, unterstützt kein System eine explizite föderierte Concurrency Control. In der Literatur wurden zwar zahlreiche Lösungsansätze vorgeschlagen, doch sie haben wenig Einfluss auf Produkte genommen, weil sie die weitverbreiteten Isolation Levels nicht berücksichtigen, die Applikationen Optimierungsmöglichkeiten auf Kosten einer eingeschränkten Kontrolle über die Konsistenz der Daten erlauben. Diese Arbeit vergleicht zunächst existierende Definitionen für Isolation Levels und entwickelt eine neuartige, formale Charakterisierung für Snapshot Isolation, dem Isolation Level des Marktführers Oracle. Anschließend werden Algorithmen zur föderierten Concurrency Control vorgestellt, die beweisbar auch unter lokaler Snapshot Isolation die korrekte Ausführung föderierter Transaktionen gewährleisten, und Isolation Levels für föderierte Transaktionen diskutiert. Die Algorithmen sind in ein prototypisches föderiertes System integriert. Performancemessungen an diesem Prototyp zeigen ihre praktische Einsetzbarkeit.Atomicity and isolation of transactions are key requirements of advanced applications in federated systems consisting of distributed and heterogeneous components. While all existing federated systems support atomicity using the two-phase commit protocol, they lack support for federated concurrency control. Many possible solutions have been proposed in the literature, but they failed to make impact on real systems because they completely ignored the widely used concept of isolation levels, which offer optimization options to applications at the cost of less rigorous control over data consistency. This thesis compares existing definitions for isolation levels and develops a new characterization for Snapshot Isolation, an isolation level provided by Oracle, the market leader in the database field. We present algorithms for federated concurrency control that provably guarantee the correct execution of federated transactions even under local Snapshot Isolation, and discuss isolation levels for federated transactions. The algorithms are integrated into a federated system prototype. Performance measurements with this prototype show the practical viability of the developed methods

    Transaktionen in föderierten Datenbanksystemen unter eingeschränkten Isolation Levels

    Get PDF
    Atomarität und Isolation von Transaktionen sind Schlüsseleigenschaften fortgeschrittener Anwendungen in föderierten Systemen, die aus verteilten, heterogenen Komponenten bestehen. Während Atomarität von praktisch allen realen Systemen durch das Zweiphasen- Commitprotokoll gewährleistet wird, unterstützt kein System eine explizite föderierte Concurrency Control. In der Literatur wurden zwar zahlreiche Lösungsansätze vorgeschlagen, doch sie haben wenig Einfluss auf Produkte genommen, weil sie die weitverbreiteten Isolation Levels nicht berücksichtigen, die Applikationen Optimierungsmöglichkeiten auf Kosten einer eingeschränkten Kontrolle über die Konsistenz der Daten erlauben. Diese Arbeit vergleicht zunächst existierende Definitionen für Isolation Levels und entwickelt eine neuartige, formale Charakterisierung für Snapshot Isolation, dem Isolation Level des Marktführers Oracle. Anschließend werden Algorithmen zur föderierten Concurrency Control vorgestellt, die beweisbar auch unter lokaler Snapshot Isolation die korrekte Ausführung föderierter Transaktionen gewährleisten, und Isolation Levels für föderierte Transaktionen diskutiert. Die Algorithmen sind in ein prototypisches föderiertes System integriert. Performancemessungen an diesem Prototyp zeigen ihre praktische Einsetzbarkeit.Atomicity and isolation of transactions are key requirements of advanced applications in federated systems consisting of distributed and heterogeneous components. While all existing federated systems support atomicity using the two-phase commit protocol, they lack support for federated concurrency control. Many possible solutions have been proposed in the literature, but they failed to make impact on real systems because they completely ignored the widely used concept of isolation levels, which offer optimization options to applications at the cost of less rigorous control over data consistency. This thesis compares existing definitions for isolation levels and develops a new characterization for Snapshot Isolation, an isolation level provided by Oracle, the market leader in the database field. We present algorithms for federated concurrency control that provably guarantee the correct execution of federated transactions even under local Snapshot Isolation, and discuss isolation levels for federated transactions. The algorithms are integrated into a federated system prototype. Performance measurements with this prototype show the practical viability of the developed methods
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