分布式缓存系统中一种优化缓存部署的图算法

数据缓存技术可以有效地减少网络拥塞,减轻服务器负载,加快信息访问速度.通过部署一组地域分布的缓存节点相互协作处理用户请求,可以进一步提高系统性能.在分布式缓存系统中,一个值得关注的问题是优化缓存的放置,使访问开销最小化.首先建立了一个理论模型来分析缓存副本放置对系统访问开销的影响.基于这个模型,缓存放置问题可以形式化地描述成一个最优化问题,提出了一种图算法来解决该问题.图算法使用修改的Dijkstra算法在访问代价图中寻找一条最短路径,该路径对应一种最优的缓存部署.理论上证明了图算法的正确性,并使用仿真实验对其性能进行评估.实验结果表明,图算法的性能优于大部分现有的分布式缓存机制.     

分布式缓存系统中一种优化缓存部署的图算法

数据缓存技术可以有效地减少网络拥塞,减轻服务器负载,加快信息访问速度.通过部署一组地域分布的缓存节点相互协作处理用户请求,可以进一步提高系统性能.在分布式缓存系统中,一个值得关注的问题是优化缓存的放置,使访问开销最小化.首先建立了一个理论模型来分析缓存副本放置对系统访问开销的影响.基于这个模型,缓存放置问题可以形式化地描述成一个最优化问题,提出了一种图算法来解决该问题.图算法使用修改的Dijkstra算法在访问代价图中寻找一条最短路径,该路径对应一种最优的缓存部署.理论上证明了图算法的正确性,并使用仿真实验对其性能进行评估.实验结果表明,图算法的性能优于大部分现有的分布式缓存机制.     

一种P2P网络信息分类检索模型研究

P2P是在分布式自治系统与异构系统之间直接进行资源、服务和信息共享的系统,分布式P2P模型中存在安全性差、流量大和搜寻时间长等弱点,为了解决这些问题,利用"局部访问"原理,提出了一种能够根据历史访问的统计的分类搜索的分布式P2P模型的搜索方法,改善了分布式P2P模型的信息搜索性能,从而为解决上述问题提供了一种有效的途径.     

可伸缩分布式动态区间映射算法

提出一种支持权重分布数据的可伸缩分布式动态区间映射算法.该算法能够在存储节点发生变化时,根据可用的资源情况立即重新均衡数据对象分布,从所有存储节点中并行迁移数据对象,且迁移的数据对象数目是最少的.在此基础上提出分布式节点地址计算算法,支持计算节点通过视图校正算法自主学习,自动适应新的系统规模,消除了现有的集中式访问性能瓶颈,使系统具有高可伸缩性.     

一种自组织资源发现模型和算法

针对具有动态性和不稳定性资源的网格计算环境的资源发现问题,提出一种基于资源索引节点的自组织资源发现模型,该模型采用了基于组的分层资源组织方式,通过信息节点管理组内资源信息,所有信息节点形成树型覆盖网络,可以在信息节点树型覆盖网络实现分布式资源定位.并提出以资源索引节点索引所有信息节点中资源的关键属性,设计了基于资源索引节点的智能资源发现算法,实验结果表明,该算法在系统负栽变化情况下,能保持稳定的性能,相比集中式资源发现算法、结构化P2P资源发现算法和分布式资源算法性能更优.     

蓝鲸分布式文件系统的分布式分层资源管理模型

为了高效地管理海量分布式存储资源,蓝鲸分布式文件系统抛弃了传统的集中式资源管理方式。实现了分布式分层资源管理模型．该模型可以管理多个存储服务器,还能支持多个元数据服务器组成的集群进行分布式元数据处理,支持各种元数据和数据的负载平衡策略．同时,该模型中的带外数据传输功能克服了系统的性能瓶颈。提高了系统支持并发访问的能力．理论分析和实际测试结果都表明此模型能够满足多种不同的需求,提供很好的性能和良好的扩展性．     

基于二维协调空间的网格工作流调度算法研究

传统的网格工作流模型中分布式工作流管理器之间没有合作,因此可能发生源调度冲突问题,另外,在现有的工作流调度算法中,参与工作流调度的工作流管理器依托于集中或半集中的层次式的资源信息服务体系,导致系统的扩展性差.为了解决这些问题,在文中,提出了一个分布式的协同工作流调度算法.该算法基于二维协调空间来管理网格中的工作流管理器.二维协调空间负责资源发现和协调调度等功能.该算法不仅可以避免性能瓶颈,而且可以增强系统的可扩展性和自主性.     

分布式OA系统中数据分布算法

在分布式OA系统中,数据资源的分布会影响整个OA系统的效率。为了能够合理进行数据资源分布,提高OA系统的效率,提出了一种基于分布式数据资源的分布模型及算法,该算法给出了可减少网络流量、降低整个分布式系统开销的数据分布方案,由此提高OA系统的整体性能,使之更能适应OA应用需要。     

基于分布式协同缓存机制的Web Proxy研究

提出了一种基于全局内存对象缓冲池的高性能分布式Web Proxy模型,通过在系统范围内构建类似于分布式共享存储器系统的缓冲池,并将分布式Web Proxy系统中访问最频繁的Web对象置于其中,则Web对象的平均服务时间缩短,提高了系统性能。通过实际Proxy服务器的访问日志进行了系统性能仿真,结果表明,该机制可以提高分布式Web Proxy服务器的性能。     

基于P2P框架的网格资源发现算法研究

由于资源数量的巨大,典型网格系统中的资源发现问题就成为关键,而现有网格中有许多的资源发现算法主要是集中或分层方法.P2P已经被认为是一种合适的分布式模型,它具有动态性、可伸缩等优点.在现有网格之上提出了一个P2P虚拟层,并据此提出了一个用于网格资源发现的分布式算法,从而解决现有网格系统中资源发现效率低、性能差、不具有伸缩性和可扩展性等一系列问题.     

面向存储服务的分布式缓存系统研究

针对分布式环境下高频率异地数据访问造成的系统性能下降的问题,对SBM模型进行改进,提出分布式缓存系统D-Cache,给出基于最优价值度的缓存文件替换算法——OCV。数字模拟实验结果证明,与DartCache系统相比,D-Cache系统能更有效地减少系统访问延迟,增加吞吐量,提高分布式环境下系统的性能。     

Memory and Network Architecture Interaction in an Optically Interconnected Distributed Shared Memory System

This paper develops a performance model of an optically interconnected parallel computer system operating in a distributed shared memory environment. The performance model is developed to reflect the impact of low level optical media access protocol and optical device switching latency on high level system performance. This enables the model to predict the performance impact of supporting distributed shared memory with different address allocation schemes and media access protocols. The passive star-coupled photonic network operates through wavelength division multiple access. Two media access protocols are examined for this WDM network, both are designed to operate in a multiple-channel multiple-access environment and require each node to possess a wavelength tunable transmitter and a fixed (or slow tunable) receiver. A semi-Markov model has been developed to study the interaction of the distributed shared memory architecture and the two access protocols of the photonic network. This analytical model has been validated by extensive simulation. The model is then used to examine the system performance with varying numbers of nodes and wavelength channels and varying, memory and channel access times.     

分布式应用访问控制策略精化冲突分析

随着云技术的发展,分布式应用平台朝着弹性资源和环境动态变迁的方向发展。分布式应用访问控制策略精化计算与资源和环境相关,也需要较强的性能与这种动态性相适应。现有的访问控制策略空间冲突分析方法虽然可以用于分布式访问控制策略精化中的策略冲突分析,但是该类算法以权限赋值单元为单位计算,计算粒度过细导致性能较低。提出了基于集合求交递推算法,以权限赋值单元集合为单位计算策略冲突来提高计算粒度。理论分析与实验结果表明该算法具有较高性能, 适用于云平台策略精化计算的高性能的需求。     

网络疑似入侵环境下的最优接口访问控制模型仿真

在网络疑似入侵环境下通过最优接口访问控制实现网络入侵的可靠性拦截,保障网络安全。传统方法采用自由链路分散控制模型进行网络入侵检测和接口访问控制,在受到较大的特征干扰下,入侵访问控制和拦截性能不好。提出一种基于自适应循环堆栈接口调度的网络疑似入侵环境下的最优接口访问控制模型。进行接口访问控制模型总体设计及组件模块分析,接口访问控制系统包括通信库、协议库、核心控制库和资源库,采用小波包自适应波束调制方法进行入侵检测算法设计,作为接口访问控制系统软件核心。通过SDICmdCon寄存器设置网络疑似入侵环境下的最优接口的内核,在嵌入式Linux环境下通过自适应循环堆栈接口调度实现接口访问控制的软件开发。仿真结果表明,采用该模型进行网络入侵检测,准确检测性能较好,通过最优接口访问控制,实现对网络入侵数据的准确识别和拦截。     

DCSACA: distributed constraint service-aware collaborative access algorithm based on large-scale access to the Internet of Things

With the rapid development of the smart city and the Internet Plus-themed multi-network applications, it is becoming increasingly difficult for the data access center for the Internet of Things (DACIOT) to meet large-scale users’ service requirements with low latency and high quality while sending service access requests. This paper first converts the problem of a large number of access requests to DACIOT into a distributed constraint optimization problem. Then, in order to address the optimization problem, a dynamic multi-constraint service-aware collaborative access algorithm is proposed based on dynamic load feedback from the access nodes, which can effectively reduce network congestion through load feedback and improve access performance. The algorithm firstly defines the dynamic context load sensing model, which is able to detect the load metrics of access clusters and assist access servers to work together to improve the availability of DACIOT, then it uses a heuristic falling search algorithm to search for the optimal resource on the basis of this model, after which it analyzes the convergence of the access algorithm. Experimental results show that the algorithm can effectively improve the rate of success, lower the network delay of access requests and reduce network jitter when accessing DACIOT.     

Transaction Processing in a Mobile,Multi-Database Environment

Current distributed and multi-database systems are designed to allow timely and reliable access to large amounts of data distributed at different locations. Changes in current technology now allow users to access this data via a wide variety of devices through a diverse communication medium. A mobile data access system is an environment in which a wireless-mobile computing environment is superimposed upon a multi-database environment in order to realize anywhere, anytime access capability. As a potentially large number of users may siultaneously access the available data, there are several issues involved in the ability to concurrently manage transactions. Current multi-database concurrency control schemes do not efficiently manage these accesses because they do not address the limited bandwidth and frequent disconnections associated with wirelessnetworks.This paper first introduces the so-called mobile data access system (MDAS) and then proposes a new hierarchical concurrency control algorithm. The proposed concurrency control algorithm, v-lock, uses global locking tables created with semantic information contained within the hierarchy. The locking tables are subsequently used to serialize global transactions, and detect and remove global deadlocks. The performance of the new algorithm is simulated and the results are presented. In addition (through simulation) the performance of the proposed algorithm has been compared and contrasted against the site graph method, the potential conflict graph method, and the forced conflict method     

Techniques for Scheduling I/O in a High Performance Multimedia-on-Demand Server

One of the key components of a multiuser multimedia-on-demand system is the data server. Digitalization of traditionally analog data such as video and audio, and the feasibility of obtaining network bandwidths above the gigabit-per-second range, are two important advances that have made possible the realization, in the near future, of interactive distributed multimedia systems. Secondary-to-main memory I/O technology has not kept pace with advances in networking, main memory, and CPU processing power. Consequently, the performance of the server has a direct bearing on the overall performance of such a system. In this paper, we present a highperformance solution to the I/O retrieval problem in a distributed multimedia system. We develop a model for the architecture of a server for such a system. Parallelism of data retrieval is achieved by striping the data across multiple disks. We present the algorithms for server operation when servicing a constant number of streams, as well as the admission control policy for accepting requests for new streams. The performance of any server ultimately depends on the data access patterns. Two modifications of the basic retrieval algorithm are presented to exploit data access patterns in order to improve system throughput and response time. Finally, we present preliminary performance results of these algorithms on the IBM SP1 and Intel Paragon parallel computers.     

Efficient LRU-based buffering in a LAN remote caching architecture

The possibility of fast access to the main memory of remote sites has been advanced as a potential performance improvement in distributed systems. Even if a page is not available in local memory, sites need not do a disk access. Instead, the sites can use efficient mechanisms that support rapid request/response exchanges in order to access pages that are currently buffered at a remote site. Hardware and software support in such a remote caching architecture must also include algorithms that determine which pages should be buffered at what sites. When each site uses the classic LRU replacement algorithm, performance can be much worse than optimal in many system configurations. Because sites do not coordinate individual decisions, overall system buffering/caching decisions yield very inefficient global configurations. This paper proposes an easily implementable modification of the LRU replacement algorithm for LAN environments that reduces replication. The algorithm substantially improves hit-ratios-and thus performance-over a wide range of parameters. The relatively simple LAN topology implies that much less state information need be available for good replacement decisions compared to general network topologies. Two implications of two variations of the algorithm are explored. In an environment where the network is not a performance bottleneck, and where performance is memory-limited, performance of the proposed replacement algorithm is shown to be close to optimal     

Formal approach to fault diagnosis in distributed discrete event systems with OBDD

In this paper, we study the fault diagnosis problem for distributed discrete event systems. The model assumes that the system is composed of distributed components which are modeled in labeled Petri nets and interact with each other via sets of common resources (places). Further, a component’s own access to a common resource is an observable event. Based on the diagnoser approach proposed by Sampath et al., a distributed fault diagnosis algorithm with communication is presented. The distributed algorithm assumes that the local diagnosis process can exchange messages upon the occurrence of observable events. We prove the distributed diagnosis algorithm is correct in the sense that it recovers the same diagnostic information as the centralized diagnosis algorithm. Furthermore, we introduce the ordered binary decision diagrams (OBDD) in order to manage the state explosion problem in state estimation of the system.