Recognizing the impact of reconfiguration on the QoS of running systems is especially necessary for choosing an appropriate approach to dealing with dynamic evolution of mission-critical or non-stop business systems. The rationale is that the impaired QoS caused by inappropriate use of dynamic approaches is unacceptable for such running systems. To predict in advance the impact, the challenge is two-fold. First, a unified benchmark is necessary to expose QoS problems of existing dynamic approaches. Second, an abstract representation is necessary to provide a basis for modeling and comparing the QoS of existing and new dynamic reconfiguration approaches. Our previous work [8] has successfully evaluated the QoS assurance capabilities of existing dynamic approaches and provided guidance of appropriate use of particular approaches. This paper reinvestigates our evaluations, extending them into concurrent and parallel environments by abstracting hardware and software conditions to design an evaluation context. We report the new evaluation results and conclude with updated impact analysis and guidance.

A major challenge of dynamic reconfiguration is Quality of Service (QoS) assurance, which is meant to reduce application disruption to the minimum for the system's transformation. However, this problem has not been well studied. This paper investigates the problem for component-based software systems from three points of view. First, the whole spectrum of QoS characteristics is defined. Second, the logical and physical requirements for QoS characteristics are analyzed and solutions to achieve them are proposed. Third, prior work is classified by QoS characteristics and then realized by abstract reconfiguration strategies. On this basis, quantitative evaluation of the QoS assurance abilities of existing work and our own approach is conducted through three steps. First, a proof-of-concept prototype called the reconfigurable component model is implemented to support the representation and testing of the reconfiguration strategies. Second, a reconfiguration benchmark is proposed to expose the whole spectrum of QoS problems. Third, each reconfiguration strategy is tested against the benchmark and the testing results are evaluated. The most important conclusion from our investigation is that the classified QoS characteristics can be fully achieved under some acceptable constraints.

Abstract The significance of QoS‐assurance is being increasingly recognized by both the research and wider communities. In the latter case, this recognition is driven by the increasing adoption by business of 24/7 software systems and the QoS decline that end‐users experience when these systems undergo dynamic reconfiguration. At the beginning of 2006, the author set up a project named DynaQoS©‐RDF (QoS‐assurance of Dynamic Reconfiguration on Reconfigurable Dataflow Model), which was then sponsored by the CQ University Australia. Over the last two years, the author has investigated QoS‐assurance for dataflow systems, which are characterized by the pipe‐and‐filter architecture. The research has addressed issues such as: the global consistency of protocol transactions, the necessary and sufficient conditions for QoS‐assurance, execution overhead control for reconfiguration, state transfer for stateful components, and the design of a QoS benchmark. This paper discusses these research issues. It also proposes various QoS strategies and presents a benchmark for evaluating QoS‐assurance strategies for the dynamic reconfiguration of dataflow systems. This benchmark is implemented using the DynaQoS©‐RDF v1.0 software platform. Various strategies, including those from the research literature are benchmarked, and the best efforts for QoS‐assurance are identified. Copyright © 2008 John Wiley & Sons, Ltd.

In this paper, we firstly review the concerned issues on dynamic reconfiguration of non-stop dataflow systems with QoS requirement and what the related work have been done on these issues. Then we present our research by focusing on reconfiguration automation – automated reconfiguration planning and automated execution scheduling with taking the concerned issues on board. Significantly the automated planning removes the reliance of reconfiguration correctness on change administrators. Structures, such as Version-Visibility, Restrict-Segment and Route-Map, along with planning and scheduling algorithms, are proposed in this paper as the fundamentals to automate reconfiguration for maintaining the system’s QoS and preserving the application integrity. All the proposed structures and algorithms have been fully implemented as an architectural meta-model called the RDF (Reconfigurable Dataflow) model. In this paper a dataflow system: the DEDSS (Data Encryption & Digital Signature System) is studied as a typical case on the RDF to demonstrate the effectiveness of our approaches to automating seamless and QoS-ensured reconfiguration of non-stop dataflow systems.

Although many approaches to dynamic reconfiguration have been proposed, how the impact of reconfiguration on system QoS can be controlled has not been addressed adequately so far. In this paper, we propose an approach to dynamic reconfiguration of distributed data flow systems. It is an improvement of our previous work for dynamic reconfiguration with QoS management into distributed environment. Our approach has three features. First, it uses version control, flow trace, and reconfiguration scheduling to avoid logical and physical impact on system QoS. Second, it plans a reconfiguration in a totally automatic way. Third, it executes a reconfiguration by a decentralized protocol to reduce reconfiguration time in distributed environment. We adopt our approach to the reconfiguration of a real world application, the data encryption and digital signature system. Experimental results show that our approach has significant advantages in impact control comparing with other existing approaches.

Metacomputing aims at using the computing power of computers linked by networks for various applications, which used to be tackled by dedicated supercomputers a few years ago. Web-based metacomputing offers a cheap and efficient solution for parallel and distributed computing by exploiting idle cycles from the Internet. Research literatures have been published to report the state of the art of metacomputing by addressing the developed prototypes – architecture, support methodologies and technologies, programming APIs, example benchmarks and experimental performances. This paper tries to answer the question: why the metacomputing system is undesirable in performance, applicability and reliability. In this paper, the system’s components are modelled as three roles: Client, Worker and Manager. Their performances are individually investigated in terms of the Theory of Constraint: Objectives, Requirements, Prerequisites, Conflicts and Injections for identifying core problems and exploring efficient solutions. The main contribution of this paper is to be a very first literature as conceptual guidelines for design and optimisation of metacomputing systems.