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Specification and Management of QoS in Real-Time Databases Supporting Imprecise Computations
Linköping University, Department of Computer and Information Science, RTSLAB. Linköping University, The Institute of Technology.
Linköping University, Department of Computer and Information Science, RTSLAB. Linköping University, The Institute of Technology.
Dept. of Computer Science, University of Virginia, Charlottesville, USA.
2006 (English)In: IEEE Transactions on Computers, ISSN 0018-9340, Vol. 55, no 3, 304 - 319 p.Article in journal (Refereed) Published
Abstract [en]

Real-time applications such as e-commerce, flight control, chemical and nuclear control, and telecommunication are becoming increasingly sophisticated in their data needs, resulting in greater demands for real-time data services that are provided by real-time databases. Since the workload of real-time databases cannot be precisely predicted, they can become overloaded and thereby cause temporal violations, resulting in damage or even a catastrophe. Imprecise computation techniques address this problem and allow graceful degradation during overloads. In this paper, we present a framework for QoS specification and management consisting of a model for expressing QoS requirements, an architecture based on feedback control scheduling, and a set of algorithms implementing different policies and behaviors. Our approach gives a robust and controlled behavior of real-time databases, even for transient overloads and with inaccurate runtime estimates of the transactions. Further, performance experiments show that the proposed algorithms outperform a set of baseline algorithms that uses feedback control.

Place, publisher, year, edition, pages
2006. Vol. 55, no 3, 304 - 319 p.
Keyword
Real-time and embedded systems, real-time data services, imprecise computation, feedback control, modeling techniques
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-12635DOI: 10.1109/TC.2006.45OAI: oai:DiVA.org:liu-12635DiVA: diva2:16748
Available from: 2007-10-17 Created: 2007-10-17 Last updated: 2009-02-10
In thesis
1. QoS Control of Real-Time Data Services under Uncertain Workload
Open this publication in new window or tab >>QoS Control of Real-Time Data Services under Uncertain Workload
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Real-time systems comprise computers that must generate correct results in a timely manner. This involves a wide spectrum of computing systems found in our everyday life ranging from computers in rockets to our mobile phones. The criticality of producing timely results defines the different types of realtime systems. On one hand, we have the so-called hard real-time systems, where failing to meet deadlines may result in a catastrophe. In this thesis we are, however, concerned with firm and soft real-time systems, where missing deadlines is acceptable at the expense of degraded system performance. The usage of firm and soft real-time systems has increased rapidly during the last years, mainly due to the advent of applications in multimedia, telecommunication, and e-commerce. These systems are typically data-intensive, with the data normally spanning from low-level control data, typically acquired from sensors, to high-level management and business data. In contrast to hard real-time systems, the environments in which firm and soft real-time systems operate in are typically open and highly unpredictable. For example, the workload applied on a web server or base station in telecommunication systems varies according to the needs of the users, which is hard to foresee. In this thesis we are concerned with quality of service (QoS) management of data services for firm and soft real-time systems. The approaches and solutions presented aim at providing a general understanding of how the QoS can be guaranteed according to a given specification, even if the workload varies unpredictably. The QoS specification determines the desired QoS during normal system operation, and the worst-case system performance and convergence rate toward the desired setting in the face of transient overloads. Feedback control theory is used to control QoS since little is known about the workload applied on the system. Using feedback control the difference between the measured QoS and the desired QoS is formed and fed into a controller, which computes a change to the operation of the real-time system. Experimental evaluation shows that using feedback control is highly effective in managing QoS such that a given QoS specification is satisfied. This is a key step toward automatic management of intricate systems providing real-time data services.

Place, publisher, year, edition, pages
Institutionen för datavetenskap, 2007. 244 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1143
Keyword
real-time system, database, feedback control
National Category
Computer Science
Identifiers
urn:nbn:se:liu:diva-10016 (URN)978-91-85895-49-6 (ISBN)
Public defence
2007-11-15, Planck, Fysikhuset, Linköpings universitet, 13:15 (English)
Opponent
Supervisors
Available from: 2007-10-17 Created: 2007-10-17 Last updated: 2009-04-22

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Amirijoo, MehdiHansson, Jörgen

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