18173287
Performance of Fault-Tolerant Data and Compute Intensive Programs over a Network of Workstations
A well-known structuring technique for a wide class of parallel applications is the bag of tasks, which allows a computation to be partitioned dynamically between a collection of concurrent processes. This paper describes a fault-tolerant implementation of this structure using atomic actions (atomic transactions) to operate on persistent objects, which are accessed in a distributed setting via a Remote Procedure Call (RPC). The system developed is suited to parallel execution of data and compute intensive programs that require persistent storage and fault tolerance facilities. The suitability of the system is examined in the context of the measured performance of three specific applications; ray tracing, matrix multiplication and Cholesky factorisation. The measured performance compares well with that predicted by analysis of the applications based on benchmark measurement of hardware parameters. The same analysis allows modelling of hardware upgrades.
5328327
Fault-tolerant parallel applications using queues and actions
There are many techniques supporting execution of large computations over a network of workstations (NOW) but data intensive computations are usually run on high performance parallel machines. A NOW comprising individual user's machines typically has a low performance interconnect and suffers arbitrary changes of availability. Exploiting such resources to execute data intensive computations is difficult but even in a more constrained environment there is an unfulfilled need for fault-tolerance. The structuring approach presented fulfills this need. Performance exceeding 100 Mflop/s is demonstrated for large fault-tolerant out of core examples of matrix multiplication and Cholesky factorisation using five 133 MHz Pentium compute machines.
17495706
Fault-tolerance in distributed query processing
Fault-tolerance has long been a feature of database systems, with transactions supporting the structuring of applications so as to ensure continuation of updating applications in spite of machine failures. For read-only queries the perceived wisdom has been that support for fault-tolerance is too expensive to be worthwhile. Distributed query processing is coming to be seen as a promising way of implementing applications that combine structured data and analysis operations in dynamic distributed settings such as computational grids. Such a query may be long-running and having to redo the whole query after a failure may cause problems (e.g. if the result may trigger business or safety critical activities). This work describes and evaluates a new scheme for adding fault-tolerance to distributed query processing through a rollback-recovery mechanism. The high level expression of user requests in a physical algebra offers opportunities for tuning the fault-tolerance provision so as to reduce the cost, and give better performance than employment of generic fault-tolerance mechanisms at the lowest level of query processing. This paper outlines how the publicly-available OGSA-DQP computational grid-based distributed query processing system can be modified to include support for fault-tolerance and presents a performance evaluation which includes measurements of the cost of both protocol overheads and rollback-recovery, for a set of example distributed queries.
40619191
The Design, Implementation and Evaluation of an ODMG Compliant, Parallel Object Database Server
This paper describes the design, implementation and evaluation of a parallel object database server. While a number of research groups and companies now provide object database servers designed to run on uniprocessors, there has been surprisingly little work on the exploitation of parallelism to provide scalable performance in Object Database Management Systems (ODBMS). The work described in this paper takes as its starting-point the Object Database Management Group (ODMG) standard for object databases, thereby allowing the project to focus on research into parallelism, rather than on the ODBMS interfaces. The system is designed to run on a distributed memory parallel machine, and the paper describes the key issues and design decisions including: parallel query optimisation and execution, flow control, support for user-defined operations in queries, object distribution, cache management and navigational client access. The work shows that the significant differences between the object and relational database paradigms lead to significant differences in the designs of parallel servers to support these two paradigms. The paper presents an extensive performance analysis of the prototype systems which shows that good performance can be achieved on a cluster of linux PCs.
37610017
Validated Cost Models for Parallel OQL Query Processing
Query cost models are widely used, both for performance analysis and for comparing execution plans during query optimisation. In essence, a cost modelp redicts where time is being spent during query evaluation. Although many cost models have been proposed, for serial, parallel and distributed database systems, surprisingly few of these have been validated against real systems. This paper presents cost models for the parallel evaluation of ODMG OQL queries, which have been compared with experimental results obtained using the Polar object database system. The paper describes the validation of the cost model for a collection of queries, using three join algorithms over the OO7 benchmark database. The results show that the cost model generally both ranks alternative plans appropriately, and gives a useful indication of the response times that can be expected from a plan. The paper also illustrates the application of the cost model by highlighting the contributions of different features and operations to query response times.
13121681
A parallel algebra for object databases
The paper describes an algebra for use with parallel object databases, and in particular ODMG compliant databases with OQL. Although there have been many proposals for parallel relational database systems, there has been much less work on parallel object databases, and on parallel query processing for object databases. The parallel algebra presented in the paper is an extension of an existing physical algebra for OQL, and has an important role during query optimization, and for describing execution plans. The paper presents not only the algebra, but also its role in the architecture of a parallel database.
6609571
Efficient Techniques for Feature-Based Image/Video Access and Manipulation
Efficient, effective methods for indexing, searching, and retrieving images and videos from large archives are critical techniques required in visual information systems (VIS) applications. Users need a more powerful method for searching images than just traditional text-based query (e.g., keywords). Manual creation of keywords is too time-consuming for many practical applications. Subjective descriptions based on users’ input will be neither consistent nor complete. Also, the vocabulary used in describing visual contents is usually domain specific.
1598637
Dynamic resource management heuristics for minimizing makespan while maintaining an acceptable level of robustness in an uncertain environment
Heterogeneous parallel and distributed computing systems may operate in an environment where certain system performance features degrade due to unpredictable circumstances. Robustness can be defined as the degree to which a system can function correctly in the presence of parameter values different from those assumed. This paper presents a mathematical model for quantifying robustness in a dynamic environment where task execution times estimates are known to contain errors. This research proposes, evaluates, and compares ten different dynamic heuristics for their ability to maintain or maximize the proposed dynamic robustness metric in an uncertain environment. In addition, the makespan results of the proposed heuristics are compared to a lower bound
6489448
ABC: a hypermedia system for artifact-based collaboration
Abstract : Our project is studying the process by which groups of individuals work together to build large, complex structures of ideas, and we are developing a distributed hypermedia system to support the process. This description includes a brief overview of the system, but emphasizes three components: a hypermedia data management system or graph server, a set of browsers for working with graph objects, and a set of applications for working with data contents of graph nodes. A number of research issues are raised and discussed in context, including: composite objects; anchored links; scaling up for large applications; partitioning the hypermedia graph; consistency and completeness across subgraphs; and an open, extensible architecture for applications.
38357274
Algorithms for distributing telecommunication traffic on a multiple-ring SONET-based network
Abstract We examine a problem arising in the assignment of telecommunication traffic to a set of synchronous optical network (SONET) rings. Prior SONET design algorithms determine node-to-ring assignments while concurrently prescribing an assignment of traffic to the rings. However, due to uncertain voice and data demand among client nodes, it may become necessary to revise the planned routing scheme once the true values of this data are realized. We develop a minimum cost flow algorithm for the case in which demands may be split across multiple rings, and provide a transformation to a maximum flow problem for specially structured data. The case in which each demand pair may be routed on only one ring is proven to be NP-hard, and we accordingly provide a powerful heuristic and an effective standard valid inequality generation scheme to optimally solve this problem within reasonable computational limits. The effectiveness of our approach is demonstrated on a set of randomly generated test data.
17924974
Towards effective practitioner evaluation: an exploration of issues relating to skills, motivation and evidence
Although academics are increasingly expected to undertake studies of their practice, particularly where this involves the use of learning technology, experience to date suggests that meeting this expectation has proved difficult. This paper attempts to explain this difficulty. After reviewing literature that provides a rationale for practitioner evaluation, the experiences of three projects (EFFECTS, ASTER and SoURCE) which attempted to draw on this process are described. Three main areas of difficulty are discussed: the skills and motivations of the academics involved, and the kinds of evidence (and its analysis) that ‘count’ for a given evaluation. This discussion leads to the identification of a number of problems that inhibit practitioner evaluation, including ambiguity in the nature and purpose of evaluation, and a general feeling that the function of evaluation has already been served through existing quality mechanisms. Finally, the possible implications are considered of some or all of the steps in the evaluation process being undertaken by an evaluator working alongside the academic.