2567437
Dynamic Query Operator Scheduling for Wide-Area Remote Access
Distributed databases operating over wide-area networks such as the Internet, must deal with the unpredictable nature of the performance of communication. The response times of accessing remote sources can vary widely due to network congestion, link failure, and other problems. In such an unpredictable environment, the traditional iterator-based query execution model performs poorly. We have developed a class of methods, called query scrambling, for dealing explicitly with the problem of unpredictable response times. Query scrambling dynamically modifies query execution plans on-the-fly in reaction to unexpected delays in data access. In this paper we focus on the dynamic scheduling of query operators in the context of query scrambling. We explore various choices for dynamic scheduling and examine, through a detailed simulation, the effects of these choices. Our experimental environment considers pipelined and non-pipelined join processing in a client with multiple remote data sources and delayed or possibly bursty arrivals of data. Our performance results show that scrambling rescheduling is effective in hiding the impact of delays on query response time for a number of different delay scenarios.
6459671
Extensible data management in the middle-tier
Current data management solutions are optimized for intra-enterprise, client-server applications. They depend on predictability, predefined structure and universal administrative control, and cannot easily cope with change and lack of structure. However, modern e-commerce applications are dynamic, unpredictable, organic, and decentralized, and require adaptability. eXtensible Data Management (XDM) is a new approach that enables rapid development and deployment of networked, data-intensive services by providing semantically-rich, high-performance middle-tier data management, and allows heterogeneous data from different sources to be accessed in a uniform manner. We discuss how middle tier extensible data management can benefit an enterprise, and present technical details and examples from the Index Fabric, an XDM engine we have implemented.
1844352
Supporting aggregate queries over ad-hoc wireless sensor networks
We show how the database community's notion of a generic query interface for data aggregation can be applied to ad-hoc networks of sensor devices. As has been noted in the sensor network literature, aggregation is important as a data reduction tool; networking approaches, however, have focused on application specific solutions, whereas our in-network aggregation approach is driven by a general purpose, SQL-style interface that can execute queries over any type of sensor data while providing opportunities for significant optimization. We present a variety of techniques to improve the reliability and performance of our solution. We also show how grouped aggregates can be efficiently computed and offer a comparison to related systems and database projects.
17986347
Data caching tradeoffs in client-server DBMS architectures
In this paper, we examine the performance tradeoffs that are raised by caching data in the client workstations of a client-server DBMS. We begin by presenting a range of lock-based cache consistency algorithms that arise by viewing cache consistency as a v~iant of the well-understood problem of replicated data management. We then use a detailed simulation model to study the performance of these algorithm over a wide range of workloads end system resource configurations. The results illustrate the key performance tradeoffs related to clientserver cache consistency, and should be of use to designers of next-generation DBMS prototypes and products.
7889988
Crash recovery in client-server EXODUS
In this paper, we address the correctness and performance issues that arise when implementing logging and crash recovery in a page-server environment. The issues result from two characteristics of page-server systems: 1) the fact that data is modified and cached in client database buffers that are not accessible by the server, and 2) the performance and cost trade-offs that are inherent in a client-server environment. We describe a recovery system that we have implemented for the client-server version of the EXODUS storage manager. The implementation supports efficient buffer management policies, allows flexibility in the interaction between clients and the server, and reduces the server load by generating log records at clients. We also present a preliminary performance analysis of the implementation.
2815522
Efficient Filtering of XML Documents for Selective Dissemination of Information
Information Dissemination applications are gaining increasing popularity due to dramatic improvements in communications bandwidth and ubiquity. The sheer volume of data available necessitates the use of selective approaches to dissemination in order to avoid overwhelming users with unnecessaryinformation. Existing mechanisms for selective dissemination typically rely on simple keyword matching or “bag of words” information retrieval techniques. The advent of XML as a standard for information exchangeand the development of query languages for XML data enables the development of more sophisticated filtering mechanisms that take structure information into account. We have developed several index organizations and search algorithms for performing efficient filtering of XML documents for large-scale information dissemination systems. In this paper we describe these techniques and examine their performance across a range of document, workload, and scale scenarios.
61655346
Statistics on Logic Simulation
The high costs associated with logic simulation of large VLSI based systems have led to the need for new computer architectures tailored to the simulation task. Such architectures have the potential for significant speedups over standard software based logic simulators. Several commercial simulation engines have been produced to satisfy needs in this area. To properly explore the space of alternative simulation architectures, data is required on the simulation process itself. This paper presents a framework for such data gathering activity by first examining possible sources of speedup in the logic simulation task, examining the sort of data needed in the design of simulation engines, and then presenting such data. The data contained in the paper includes information on subtask times found in standard discrete event simulation algorithms, event intensities, queue length distributions and simultaneous event distributions.
22695314
VLSI Performance Comparison of Banyan and Crossbar Communications Networks
The performance characteristics of banyan and crossbar communications networks are compared in a VLSI environment, where it is assumed that the entire network resides on a single VLSI chip and operates in a circuit switched mode. A high-level model of the space (area) and time (delay) requirements for these networks is developed and relative performance comparisons are made based on a space-time product measure. The results differ significantly from those obtained with more traditional analyses which are usually based on switch aggregate comparisons and SSI-based delay calculations. The analysis presented shows that the area required by both networks grows as 0(N2). Time delay grows as 0(N) for the crossbar, and approximately 0[ Na(log2N)2] for the banyan where 0 < a < 1. This contrasts with traditional results which yield 0(N log N) and 0(log N) switch and delay growth for banyan networks.
5720179
Enhancing privacy and trust in electronic communities
A major impediment to using recommendation systems and collective knowledge for electronic commerce is the reluctance of individuals to reveal preferences in order to find groups of people that share them. An equally important barrier to fluid electronic commerce is the lack of agreed upon trusted third parties. We propose new non-third party mechanisms to overcome these barriers. Our solutions facilitate finding shared preferences, discovering communities with shared values, removing disincentives posed by liabilities, and negotiating on behalf of a group. We adapt known techniques from the cryptographic literature to enable these new capabilities.
14976201
A General Matrix Iterative Model for Dynamic Load Balancing
Abstract Many applications require some form of load balancing in order to obtain good performance on parallel computing systems. A number of load balancing algorithms have been proposed, and implemented on real systems. However, application developers are in need of a performance tool that compares and evaluates various balancing algorithms, and helps select the best algorithm for a given application and computing platform. In this paper, we propose a matrix iterative model that can represent a wide range of dynamic load balancing algorithms. The model captures the change in task distribution over the processors due to both the application imbalance and load balancing algorithm. We also define performance measures that capture the costs of executing the parallel application and load balancing algorithm on a given computing platform. The model and the performance measures are used to compare and evaluate various load balancing algorithms. In this paper, the model is parameterized to represent three load balancing algorithms — the random, diffusion and redistribution algorithms. Model predictions and experimental measurements are compared for the parallel N -body simulation application. This application is representative of a wide class of scientific applications where time-varying workload distributions are present. The model predictions are within 20% of measured values. The performance of the three algorithms are compared, and optimal algorithm parameters are derived showing how the model can be used to both select an algorithm and set its parameters.
210844
Predictive scheduling of network processors
To provide flexibility in deploying new protocols and services, general-purpose processing engines are being placed in the datapath of routers. Such network processors (NPs) are typically simple RISC multiprocessors that perform forwarding and custom application processing of packets. The inherent unpredictability of execution time of arbitrary instruction code poses a significant challenge in providing service guarantees for data flows that compete for such processing resources in the network. However, we show that network processing workloads are highly regular and predictable, which can be exploited for scheduling purposes. We present two such predictive processor scheduling algorithms that aim at providing service guarantees as well as improving the performance of the NP by increasing the instruction data locality. Simulation results show that these algorithms provide significantly better performance than processor scheduling algorithms that do not take packet processing times into consideration.