Browsing by Subject "Real Time Systems"

Now showing 1 - 5 of 5

Open Access
Efficient fast hartley transform algorithms for hypercube-connected multicomputers
(IEEE, 1995) Aykanat, Cevdet; Derviş, A.
Although fast Hartley transform (FHT) provides efficient spectral analysis of real discrete signals, the literature that addresses the parallelization of FHT is extremely rare. FHT is a real transformation and does not necessitate any complex arithmetics. On the other hand, FHT algorithm has an irregular computational structure which makes efficient parallelization harder. In this paper, we propose a efficient restructuring for the sequential FHT algorithm which brings regularity and symmetry to the computational structure of the FHT. Then, we propose an efficient parallel FHT algorithm for medium-to-coarse grain hypercube multicomputers by introducing a dynamic mapping scheme for the restructured FHT. The proposed parallel algorithm achieves perfect load-balance, minimizes both the number and volume of concurrent communications, allows only nearest-neighbor communications and achieves in-place computation and communication. The proposed algorithm is implemented on a 32-node iPSC/21 hypercube multicomputer. High-efficiency values are obtained even for small size FHT problems. © 1995 IEEE
Open Access
An evaluation of real-time transaction management issues in mobile database systems
(Oxford University Press, 1999) Kayan, E.; Ulusoy, Özgür
A critical issue in mobile data management is to respond to real-time data access requirements of the supported application. However, it is difficult to handle real-time constraints in a mobile computing environment due to the physical constraints imposed by the mobile computer hardware and the wireless network technology. In this paper, we present a mobile database system model that takes into account the timing requirements of applications supported by mobile computing systems. We provide a transaction execution model with two alternative execution strategies for mobile transactions and evaluate the performance of the system considering various mobile system characteristics, such as the number of mobile hosts in the system, the handoff process, disconnection, coordinator site relocation and wireless link failure. Performance results are provided in terms of the fraction of real-time requirements that are satisfied.
Open Access
Research issues in real-time database systems . Survey paper
(Elsevier, 1995) Ulusoy, Özgür
Today's real-time systems are characterized by managing large volumes of data. Efficient database management algorithms for accessing and manipulating data are required to satisfy timing constraints of supported applications. Real-time database systems involve a new research area investigating possible ways of applying database systems technology to real-time systems. Management of real-time information through a database system requires the integration of concepts from both real-time systems and database systems. Some new criteria need to be developed to involve timing constraints of real-time applications in many database systems design issues, such as transaction/query processing, data buffering, CPU, and IO scheduling. In this paper, a basic understanding of the issues in real-time database systems is provided and the research efforts in this area are introduced. Different approaches to various problems of real-time database systems are briefly described, and possible future research directions are discussed. © 1995.
Open Access
A study of two transaction-processing architectures for distributed real-time data base systems
(Elsevier, 1995) Ulusoy, Özgür
A real-time data base system (RTDBS) is designed to provide timely response to the transactions of data-intensive applications. Processing a transaction in a distributed RTDBS environment presents the design choice of how to provide access to remote data referenced by the transaction. Satisfaction of the timing constraints of transactions should be the primary factor to be considered in scheduling accesses to remote data. In this article, we describe and analyze two different alternative approaches to this fundamental design decision. With the first alternative, transaction operations are executed at the sites where required data pages reside. The other alternative is based on transmitting data pages wherever they are needed. Although the latter approach is characterized by large message volumes carrying data pages, it is shown in our experiments to perform better than the other approach under most of the work loads and system configurations tested. The performance metric used in the evaluations is the fraction of transactions that satisfy their timing constraints. © 1995.
Open Access
Transaction processing in distributed active real-time database systems
(Elsevier, 1998) Ulusoy, Özgür
An active real-time database system (ARTDBS) is designed to provide timely response to the critical situations that are defined on database states. Although a number of studies have already addressed various issues in ARTDBSs, little attention has been paid to scheduling transactions in a distributed ARTDBS environment. In this paper, 2 we describe a detailed performance model of a distributed ARTDBS and investigate various performance issues in time-cognizant transaction processing in ARTDBSs. The experiments conducted evaluate the performance under various types of active workload and different distributed transaction-processing architectures. The performance metric used in the evaluations is the fraction of transactions that violate their timing constraints. We also describe and evaluate a nested transaction execution scheme that improves the real-time performance under high levels of active workload. © 1998 Elsevier Science Inc. All rights reserved.