Pinwheel Scheduling for Fault-tolerant Broadcast Disks in Real-time Database Systems

The design of programs for broadcast disks which incorporate real-time and fault-tolerance requirements is considered. A generalized model for real-time fault-tolerant broadcast disks is defined. It is shown that designing programs for broadcast disks specified in this model is closely related to the scheduling of pinwheel task systems. Some new results in pinwheel scheduling theory are derived, which facilitate the efficient generation of real-time fault-tolerant broadcast disk programs.National Science Foundation (CCR-9308344, CCR-9596282

Exploiting Data Mining Techniques for Broadcasting Data in Mobile Computing Environments

Cataloged from PDF version of article.Mobile computers can be equipped with wireless communication devices that enable users to access data services from any location. In wireless communication, the server-to-client (downlink) communication bandwidth is much higher than the client-to-server (uplink) communication bandwidth. This asymmetry makes the dissemination of data to client machines a desirable approach. However, dissemination of data by broadcasting may induce high access latency in case the number of broadcast data items is large. In this paper, we propose two methods aiming to reduce client access latency of broadcast data. Our methods are based on analyzing the broadcast history (i.e., the chronological sequence of items that have been requested by clients) using data mining techniques. With the first method, the data items in the broadcast disk are organized in such a way that the items requested subsequently are placed close to each other. The second method focuses on improving the cache hit ratio to be able to decrease the access latency. It enables clients to prefetch the data from the broadcast disk based on the rules extracted from previous data request patterns. The proposed methods are implemented on a Web log to estimate their effectiveness. It is shown through performance experiments that the proposed rule-based methods are effective in improving the system performance in terms of the average latency as well as the cache hit ratio of mobile clients

Pervasive Data Access in Wireless and Mobile Computing Environments

The rapid advance of wireless and portable computing technology has brought a lot of research interests and momentum to the area of mobile computing. One of the research focus is on pervasive data access. with wireless connections, users can access information at any place at any time. However, various constraints such as limited client capability, limited bandwidth, weak connectivity, and client mobility impose many challenging technical issues. In the past years, tremendous research efforts have been put forth to address the issues related to pervasive data access. A number of interesting research results were reported in the literature. This survey paper reviews important works in two important dimensions of pervasive data access: data broadcast and client caching. In addition, data access techniques aiming at various application requirements (such as time, location, semantics and reliability) are covered

Prefetching techniques for client server object-oriented database systems

The performance of many object-oriented database applications suffers from the page fetch latency which is determined by the expense of disk access. In this work we suggest several prefetching techniques to avoid, or at least to reduce, page fetch latency. In practice no prediction technique is perfect and no prefetching technique can entirely eliminate delay due to page fetch latency. Therefore we are interested in the trade-off between the level of accuracy required for obtaining good results in terms of elapsed time reduction and the processing overhead needed to achieve this level of accuracy. If prefetching accuracy is high then the total elapsed time of an application can be reduced significantly otherwise if the prefetching accuracy is low, many incorrect pages are prefetched and the extra load on the client, network, server and disks decreases the whole system performance. Access pattern of object-oriented databases are often complex and usually hard to predict accurately. The ..

Interactive media server with media synchronized raid storage system

We propose an efficient placement algorithm and per-disk prefetching method to effectively support interactive operations in the media server. Our placement policy is incorporated with an encoder having a special bitcount control scheme that repeatedly tunes quantization parameters to adjust the bitcounts of video frames. This encoder can generate coded frames whose sizes are synchronized with the RAID stripe size, so that when various fast-forward levels are accessed we can reduce the seek and rotational latency and enhance the disk throughput of each disk in the RAID system. In the experimental results, the proposed placement policy and bitrate control scheme can significantly improve the average service time, which can enlarge the capacity of the interactive media server

Inter-program Optimizations for Disk Energy Reduction

Compiler support for power and energy management has been shown to be effective in reducing overall power dissipation and energy consumption of programs, for instance through compiler-directed resource hibernation and dynamic frequency and voltage scaling. The multi-programming model with virtual memory presents a virtualized view of the machine such that compilers typically take single programs as input, without the knowledge of other programs that may run at the same time on the target machine. This work investigates the benefits of optimizing sets of programs with the goal of reducing overall disk energy. The two key ideas are to synchronize the disk accesses across a group of programs thereby allowing longer disk idle periods, and to utilize execution context knowledge to allocate maximal buffer sizes. The compiler inserts runtime system calls for profiling the application and disk, uses execution context in allocating buffers, and synchronizes disk accesses with an inverse barrier policy. Data prefetching has been added to mitigate the overhead of synchronization. Experimental results are based on three streaming applications and their subsets. The experiments show that inter-program optimizations can have significant disk energy savings over individually optimized programs. Applying the most aggressive inter-program optimizations result in energy savings of up to 49%, and saving 34% on average

Galley: A New Parallel File System for Parallel Applications

Most current multiprocessor file systems are designed to use multiple disks in parallel, using the high aggregate bandwidth to meet the growing I/O requirements of parallel scientific applications. Most multiprocessor file systems provide applications with a conventional Unix-like interface, allowing the application to access those multiple disks transparently. This interface conceals the parallelism within the file system, increasing the ease of programmability, but making it difficult or impossible for sophisticated application and library programmers to use knowledge about their I/O to exploit that parallelism. In addition to providing an insufficient interface, most current multiprocessor file systems are optimized for a different workload than they are being asked to support. In this work we examine current multiprocessor file systems, as well as how those file systems are used by scientific applications. Contrary to the expectations of the designers of current parallel file systems, the workloads on those systems are dominated by requests to read and write small pieces of data. Furthermore, rather than being accessed sequentially and contiguously, as in uniprocessor and supercomputer workloads, files in multiprocessor file systems are accessed in regular, structured, but non-contiguous patterns. Based on our observations of multiprocessor workloads, we have designed Galley, a new parallel file system that is intended to efficiently support realistic scientific multiprocessor workloads. In this work, we introduce Galley and discuss its design and implementation. We describe Galley\u27s new three-dimensional file structure and discuss how that structure can be used by parallel applications to achieve higher performance. We introduce several new data-access interfaces, which allow applications to explicitly describe the regular access patterns we found to be common in parallel file system workloads. We show how these new interfaces allow parallel applications to achieve tremendous increases in I/O performance. Finally, we discuss how Galley\u27s new file structure and data-access interfaces can be useful in practice