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We also present and evaluate in this paper an extension of the AED policy called Hierarchical Earliest Deadline (HED). The HED priority policy is designed to handle applications where transactions may be assigned different values and the goal of the real-time database system is to maximize the total value of the in-time transactions."
Many real-time systems rely on static scheduling algorithms. This includes cyclic scheduling, rate monotonic scheduling and fixed schedules created by off-line scheduling techniques such as dynamic programming, heuristic search, and simulated annealing. However, for many real-time systems, static scheduling algorithms are quite restrictive and inflexible. For example, highly automated agile manufacturing, command, control and communications, and distributed real-time multimedia applications all operate over long lifetimes and in highly non-deterministic environments. Dynamic real-time scheduling algorithms are more appropriate for these systems and are used in such systems. Many of these algorithms are based on earliest deadline first (EDF) policies. There exists a wealth of literature on EDF-based scheduling with many extensions to deal with sophisticated issues such as precedence constraints, resource requirements, system overload, multi-processors, and distributed systems. Deadline Scheduling for Real-Time Systems: EDF and Related Algorithms aims at collecting a significant body of knowledge on EDF scheduling for real-time systems, but it does not try to be all-inclusive (the literature is too extensive). The book primarily presents the algorithms and associated analysis, but guidelines, rules, and implementation considerations are also discussed, especially for the more complicated situations where mathematical analysis is difficult. In general, it is very difficult to codify and taxonomize scheduling knowledge because there are many performance metrics, task characteristics, and system configurations. Also, adding to the complexity is the fact that a variety of algorithms have been designed for different combinations of these considerations. In spite of the recent advances there are still gaps in the solution space and there is a need to integrate the available solutions. For example, a list of issues to consider includes: preemptive versus non-preemptive tasks, uni-processors versus multi-processors, using EDF at dispatch time versus EDF-based planning, precedence constraints among tasks, resource constraints, periodic versus aperiodic versus sporadic tasks, scheduling during overload, fault tolerance requirements, and providing guarantees and levels of guarantees (meeting quality of service requirements). Deadline Scheduling for Real-Time Systems: EDF and Related Algorithms should be of interest to researchers, real-time system designers, and instructors and students, either as a focussed course on deadline-based scheduling for real-time systems, or, more likely, as part of a more general course on real-time computing. The book serves as an invaluable reference in this fast-moving field.
Despite the growing interest in Real-Time Database Systems, there is no single book that acts as a reference to academics, professionals, and practitioners who wish to understand the issues involved in the design and development of RTDBS. Real-Time Database Systems: Issues and Applications fulfills this need. This book presents the spectrum of issues that may arise in various real-time database applications, the available solutions and technologies that may be used to address these issues, and the open problems that need to be tackled in the future. With rapid advances in this area, several concepts have been proposed without a widely accepted consensus on their definitions and implications. To address this need, the first chapter is an introduction to the key RTDBS concepts and definitions, which is followed by a survey of the state of the art in RTDBS research and practice. The remainder of the book consists of four sections: models and paradigms, applications and benchmarks, scheduling and concurrency control, and experimental systems. The chapters in each section are contributed by experts in the respective areas. Real-Time Database Systems: Issues and Applications is primarily intended for practicing engineers and researchers working in the growing area of real-time database systems. For practitioners, the book will provide a much needed bridge for technology transfer and continued education. For researchers, this book will provide a comprehensive reference for well-established results. This book can also be used in a senior or graduate level course on real-time systems, real-time database systems, and database systems or closely related courses.
In summary, this thesis sheds light on issues involved in real- time transaction scheduling, and presents new scheduling algorithms that come closer to meeting the challenges of the real-time domain."
In recent years, tremendous research has been devoted to the design of database systems for real-time applications, called real-time database systems (RTDBS), where transactions are associated with deadlines on their completion times, and some of the data objects in the database are associated with temporal constraints on their validity. Examples of important applications of RTDBS include stock trading systems, navigation systems and computer integrated manufacturing. Different transaction scheduling algorithms and concurrency control protocols have been proposed to satisfy transaction timing data temporal constraints. Other design issues important to the performance of a RTDBS are buffer management, index accesses and I/O scheduling. Real-Time Database Systems: Architecture and Techniques summarizes important research results in this area, and serves as an excellent reference for practitioners, researchers and educators of real-time systems and database systems.
This book provides an overview of both experimental and commercial real-time database systems (RTDBs) and a systematic approach to understanding, designing, and implementing them. To this end, the book is composed of four chapters: Chapter 1 “An Overview of Real-Time Database Systems” delves into the realm of RTDBs and discusses the specific requirements, transaction models, and scheduling algorithms that set RTDBs apart from conventional DBMs. Chapter 2 on “Experimental Real-Time Databases” presents various experimental RTDBs developed in academia with their architectures, features, and implementations, while chapter 3 on “Commercial Real-Time Databases” does so for systems developed and offered by commercial vendors as products or services. Eventually, chapter 4 on “Applications of Real-Time Database Systems” showcases various applications of RTDBs across different domains. This book will help researchers, graduate students and advanced professionals to get an overview of the area and to understand the main challenges and systems available.
Database systems of the next generation are likely to be inherently very complex due to the diversity of requirements placed on them. Incorporating active, real time, and temporal virtues in one database system is an arduous effort but is also a commend able one. This book presents the proceedings of the Second International Workshop on Active, Real Time, and Temporal Database Systems (ARTDB 97), held in Como, Milan, in September 1997. The aim of the workshop was to bring researchers together from the active and real time research communities, and to examine the current state of the art in active, real time, and temporal database systems. This book offers a collection of papers presented at the ARTDB 97 workshop. The papers, many of them representing proficient and tenable results, illuminate the feasibility of building database system supporting reactive behavior, while enforcing timeliness and predictability. The book contains nine papers carefully reviewed and accepted by the program committee, three invited papers written by prominent researchers in the field, and two summaries of the panel discussions held at the workshop. The program committee received seventeen submissions, where each submission was reviewed by at least three program committee members. The two panel sessions focused on predictability issues and on practical experience of active, real time, and temporal database systems. The ARTDB 97 workshop was held in cooperation with the IEEE Technical Committees on Real Time Systems and Complexity in Computing, and the ACM Special Interest Group on Manipulation of Data.
Our results reveal that the Earliest Deadline scheduling principle, upon which a number of existing priority assignment policies are based, discriminates significantly against longer transactions. This observation has motivated the development of a new dynamic priority assignment scheme that improves the chances for long transactions to meet their time constraints, thereby providing a fairer mechanism for use in multiclass RTDBS transaction scheduling."