The authors investigate the problem of object allocation in a distributed environment with virtually replicated data. The traditional approach to improving data availability in a distributed system is to replicate dat...
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ISBN:
(纸本)0818625457
The authors investigate the problem of object allocation in a distributed environment with virtually replicated data. The traditional approach to improving data availability in a distributed system is to replicate data. A high degree of replication, however, imposes a serious burden to the system when updates are performed. Data inference can be used to reduce the degree of replication in the system while still providing high data availability. A model to allocate objects under such an environment is proposed. Rules based on application semantics are developed to reduce the search space for optimal allocation. Heuristic algorithms are proposed for allocation when the reduced search space is still prohibitively large. Examples are given to illustrate the effectiveness of the proposed algorithms.
The authors introduce a simple and basic distributed deadlock detection and resolution algorithm for the one-resource model of a distributeddatabase system. The distribution database model upon which the algorithm is...
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The authors propose a distributed shared memory model based on a paged segmented two-level address space and an extended set of memory operations. In addition to the traditional read and write operations, the memory m...
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ISBN:
(纸本)0818625457
The authors propose a distributed shared memory model based on a paged segmented two-level address space and an extended set of memory operations. In addition to the traditional read and write operations, the memory model includes operations which support mapping between local and global address spaces and mapping of processes to transactions. An architecture and associated algorithm are outlined for a virtual memory management unit to provide concurrency control for transactions. Although the traditional concept of the transaction is assumed, only the aspects of concurrency control and coherence are addressed.
This paper describes how the Mercury electronic library moved from a prototype to a full production system supporting the Carnegie Mellon community. The focus is on how a critical examination of technical and user int...
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ISBN:
(纸本)0938734695
This paper describes how the Mercury electronic library moved from a prototype to a full production system supporting the Carnegie Mellon community. The focus is on how a critical examination of technical and user interface problems in the first Library Information System (LIS) at Carnegie Mellon translated into the design of a second generation system, LIS II. Built on a platform of small, distributed computers rather than a large, central mainframe, LIS II demonstrates that a distributed electronic library is usable and affordable. Bibliographic and full text databases in LIS II reside on different RISC servers, transparent to the user. distributed retrieval is integrated with other network services, such as the file system, authentication and protection, electronic mail and printing. Different user interfaces are provided for different machines. LIS II delivers information in ASCII and bitmapped `page image' format to the user's desktop. It uses standards as much as possible, including the Z39.50 retrieval protocol, and supports two retrieval engines.
The authors implemented a parallel hash join algorithm on a Symmetry S81 shared-everything multiprocessor environment and evaluated the performance. They evaluated the input/output (I/O) performance on a multiple-disk...
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ISBN:
(纸本)0818625457
The authors implemented a parallel hash join algorithm on a Symmetry S81 shared-everything multiprocessor environment and evaluated the performance. They evaluated the input/output (I/O) performance on a multiple-disk environment, and showed linear performance increase up to eight disks. The performance of the implemented join operation was examined on each phase, and the effect of parallel processing by the multiprocessor and the multiple disks was clarified. It was concluded from the experimental result that on such a shared-everything multiprocessor system parallelism could be easily exploited for the construction of high-performance relational databasesystems.
The authors present a propagation mechanism, called the commit propagation mechanism (CPM), which increases the availability of data for read-only transactions. The proposed mechanism is piggy-backed on the messages u...
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ISBN:
(纸本)0818625457
The authors present a propagation mechanism, called the commit propagation mechanism (CPM), which increases the availability of data for read-only transactions. The proposed mechanism is piggy-backed on the messages used in the two-phase commit protocol. The CPM was combined with the standard quorum protocol in two different replicated databasesystems. In a fully replicated database, CPM allows any read-only transaction to execute locally at a single site without the need for any communication overhead. In a partially replicated database, CPM either ensures that the set of copies residing at a site are mutually consistent, or indicates which copies violate such consistency.
A range of architectures have emerged which support real-time cooperative user interfaces. These architectures have tended to centralize the management of the interface and thus provide only limited support for user-c...
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ISBN:
(纸本)0897915429
A range of architectures have emerged which support real-time cooperative user interfaces. These architectures have tended to centralize the management of the interface and thus provide only limited support for user-centred development and interface tailoring. This paper considers the problems associated with the development of tailorable cooperative interfaces and proposes an architecture which allows such interfaces to be developed using an incremental, user-centred approach. The architecture presented in this paper has emerged within the context of a project investigating cooperative interface development for UK air traffic control. We conclude that the architecture is equally applicable to other Command and Control domains, where a shared information space forms the focus for the work taking place.
In this paper, we describe a loose coupling approach to integrate molecular biology databases that is based on concepts from graphical user interfaces. The system allows the user to custom build a graphical environmen...
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ISBN:
(纸本)0818627557
In this paper, we describe a loose coupling approach to integrate molecular biology databases that is based on concepts from graphical user interfaces. The system allows the user to custom build a graphical environment in which a uniform set of commands is provided for all the databases chosen to be members of that environment. The paper also includes preliminary description of a system, currently under development, that provides this integration. The system is designed to satisfy a few principles that guarantee that no degradation of previously existing user skills will occur and that the system can be tailored to the needs of different classes of users. The design goals of the system also include operation and database extensibility and robustness in the sense that only a minimal amount of effort is required to accommodate changes in individual database.
We present two distributed algorithms for dynamic replication of a data-item in communication networks. The algorithms are adaptive in the sense that they change the replication scheme of the item (i.e. the set of pro...
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ISBN:
(纸本)0897915194
We present two distributed algorithms for dynamic replication of a data-item in communication networks. The algorithms are adaptive in the sense that they change the replication scheme of the item (i.e. the set of processors at which the data-item is replicated), as the read-write pattern of the processors in the network changes. Each algorithm continuously moves the replication scheme towards an optimal one, where optimality is defined with respect to different objective functions. One algorithm optimizes the communication cost objective function, and the other optimizes the communication time. We also provide a lower bound on the performance of any dynamic replication algorithm.
An active area of current research is the use of semantics in concurrency control. Simulations using a new concurrency control protocol, called complex two-phase locking, can quantify the benefits of using semantics w...
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ISBN:
(纸本)0897914724
An active area of current research is the use of semantics in concurrency control. Simulations using a new concurrency control protocol, called complex two-phase locking, can quantify the benefits of using semantics within long-duration transaction systems. It is then possible to determine if the benefits gained are worth the human effort required to obtain the semantics.
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