Object and process migration in a single-address-space distributed system

In a distributed system framework, program interactions can be modelled by using typed objects according to client/server relationships. The operations defined by a given type are the services that may be provided by an object of this type to a client process. When the process and the object are located in different nodes, migrations may represent valid alternatives to remote procedure calls. Migration of the server object causes the memory area storing the internal representation of this object to be copied into the node of the client process. Migration of the client process causes execution of this process to proceed in the node of the server object. This paper proposes migration paradigms with reference to a memory environment implementing the notion of a single address space. The discussion takes a number of salient issues into consideration, including performance, memory configurations for object storage, and the strategies for memory management.     

Techniques for update handling in the enhanced client-server DBMS

The Client-Server computing paradigm has significantly influenced the way modern Database Management Systems are designed and built. In such systems, clients maintain data pages in their main-memory caches, originating from the server's database. The Enhanced Client-Server architecture takes advantage of all the available client resources, including their long-term memory. Clients can cache server data into their own disk units if these data are part of their operational spaces. However, when updates occur at the server, a number of clients may need to not only be notified about these changes, but also obtain portions of the updates as well. In this paper, we examine the problem of managing server imposed updates that affect data cached on client disk managers. We propose a number of server update propagation techniques in the context of the Enhanced Client-Server DBMS architecture, and examine the performance of these strategies through detailed simulation experiments. In addition, we study how the various settings of the network affect the performance of these policies     

基于OS／2的客户／服务器体系结构

本文阐述了客户／服务器计算的特点，介绍了ＯＳ／２２．１操作系统为客户／服务器计算模式所提供的各类支持。最后，就以ＯＳ／２为操作系统构建客户／服务器结构的可能模式进行了分析与讨论。     

基于P2P网络的资源发现算法研究

P2P是从传统的旧客户端一服务器的模式中脱离出的一种新型网络体系结构,这种体系结构内的每一台计算机拥有着相同的能力,同时也肩负着同样的责任。P2P技术已经去除了集中式的服务器,让节点间实现直接交换服务和资源。文章基于P2P网络,研究了资源发现算法。     

Periodic broadcast and patching services - implementation,measurement and analysis in an internet streaming video testbed

Multimedia streaming applications can consume a significant amount of server and network resources. Periodic broadcast and patching are two approaches that use multicast transmission and client buffering in innovative ways to reduce server and network load, while at the same time allowing asynchronous access to multimedia streams by a large number of clients. Current research in this area has focussed primarily on the algorithmic aspects of these approaches, with evaluation performed via analysis or simulation. In this paper, we describe the design and implementation of a flexible streaming video server and client test bed that implements both periodic broadcast and patching, and explore the issues that arise when implementing these algorithms using laboratory and internet-based test beds. We present measurements detailing the overheads associated with the various server components (signaling, transmission schedule computation, data retrieval and transmission), the interactions between the various components of the architecture, and the overall end-to-end performance. We also discuss the importance of an appropriate server application-level caching policy for reducing the needed disk bandwidth at the server. We conclude with a discussion of the insights gained from our implementation and experimental evaluation.Subhabrata Sen: The work of this author was conducted while he was at the University of Massachusetts.     

The “Always Best Packet Switching” architecture for SIP-based mobile multimedia services

This paper presents a distributed architecture for the provision of seamless and responsive mobile multimedia services. This architecture allows its user applications to use concurrently all the wireless network interface cards (NICs) a mobile terminal is equipped with. In particular, as mobile multimedia services are usually implemented using the UDP protocol, our architecture enables the transmission of each UDP datagram through the “most suitable” (e.g. most responsive, least loaded) NIC among those available at the time a datagram is transmitted. We term this operating mode of our architecture Always Best Packet Switching (ABPS). ABPS enables the use of policies for load balancing and recovery purposes. In essence, the architecture we propose consists of the following two principal components: (i) a fixed proxy server, which acts as a relay for the mobile node and enables communications from/to this node regardless of possible firewalls and NAT systems, and (ii) a proxy client running in the mobile node responsible for maintaining a multi-path tunnel, constructed out of all the node's NICs, with the above mentioned fixed proxy server. We show how the architecture supports multimedia applications based on the SIP and RTP/RTCP protocols, and avoids the typical delays introduced by the two way message/response handshake of the SIP signaling protocol. Experimental results originated from the implementation of a VoIP application on top of the architecture we propose show the effectiveness of our approach.     

Toward Maximizing the Quality of Results of Dependent Tasks Computed Unreliably

This paper studies the problem of maximizing the number of correct results of dependent tasks computed unreliably. We consider a distributed system composed of a reliable server that coordinates the computation of a massive number of unreliable workers. Any worker computes correctly with probability p < 1. Any incorrectly computed task corrupts all dependent tasks. The goal is to determine which tasks should be computed by the (reliable) server and which by the (unreliable) workers, and when, so as to maximize the expected number of correct results, under a constraint d on the computation time. This problem is motivated by distributed computing applications that persist partial results of computations for future use in other computations and that want to ensure that the persisted results are of high quality. We show that this optimization problem is NP-hard. Then we study optimal scheduling solutions for the mesh with the tightest deadline. We present combinatorial arguments that describe all optimal solutions for two ranges of values of worker reliability p, when p is close to zero and when p is close to one.     

A computation offloading scheme on handheld devices

In this paper, we present a computation offloading scheme on handheld devices. This scheme partitions an ordinary program into a client–server distributed program, such that the client code runs on the handheld device and the server code runs on the server. Our partition analysis and program transformation guarantee correct distributed execution under all possible execution contexts. We give a polynomial time algorithm to find the optimal program partition for given program input data. We use an option-clustering approach to handle different program partitions for different program execution options. Experimental results show significant improvement of performance and energy consumption on an HP IPAQ handheld device through computation offloading.     

TRUSS: a reliable, scalable server architecture

Traditional techniques that mainframes use to increase reliability -special hardware or custom software - are incompatible with commodity server requirements. The Total Reliability Using Scalable Servers (TRUSS) architecture, developed at Carnegie Mellon, aims to bring reliability to commodity servers. TRUSS features a distributed shared-memory (DSM) multiprocessor that incorporates computation and memory storage redundancy to detect and recover from any single point of transient or permanent failure. Because its underlying DSM architecture presents the familiar shared-memory programming model, TRUSS requires no changes to existing applications and only minor modifications to the operating system to support error recovery.     

基于CPCI总线的串口服务器模块设计与实现

针对串口通信的局限性,为满足串口通信设备快速灵活接入TCP／IP网络需求,提出了一种基于CPCI总线的串口服务器模块的设计方案。给出了串口服务器模块的系统体系结构,并对硬件结构、板载嵌入式软件和客户端软件3方面做了详细介绍,最后比较了串口服务器模块与传统串口服务器的区别,分析了其主要应用模式。实现了RS232／422串口与TCP／IP网络之间数据的双向透明传输、远程配置管理和数据共享的功能。     

Evaluating ARM HPC clusters for scientific workloads

The power consumption of modern high‐performance computing (HPC) systems that are built using power hungry commodity servers is one of the major hurdles for achieving Exascale computation. Several efforts have been made by the HPC community to encourage the use of low‐powered system‐on‐chip (SoC) embedded processors in large‐scale HPC systems. These initiatives have successfully demonstrated the use of ARM SoCs in HPC systems, but there is still a need to analyze the viability of these systems for HPC platforms before a case can be made for Exascale computation. The major shortcomings of current ARM‐HPC evaluations include a lack of detailed insights about performance levels on distributed multicore systems and performance levels for benchmarking in large‐scale applications running on HPC. In this paper, we present a comprehensive evaluation of results that covers major aspects of server and HPC benchmarking for ARM‐based SoCs. For the experiments, we built an unconventional cluster of ARM Cortex‐A9s that is referred to as Weiser and ran single‐node benchmarks (STREAM, Sysbench, and PARSEC) and multi‐node scientific benchmarks (High‐performance Linpack (HPL), NASA Advanced Supercomputing (NAS) Parallel Benchmark, and Gadget‐2) in order to provide a baseline for performance limitations of the system. Based on the experimental results, we claim that the performance of ARM SoCs depends heavily on the memory bandwidth, network latency, application class, workload type, and support for compiler optimizations. During server‐based benchmarking, we observed that when performing memory intensive benchmarks for database transactions, x86 performed 12% better for multithreaded query processing. However, ARM performed four times better for performance to power ratios for a single core and 2.6 times better on four cores. We noticed that emulated double precision floating point in Java resulted in three to four times slower performance as compared with the performance in C for CPU‐bound benchmarks. Even though Intel x86 performed slightly better in computation‐oriented applications, ARM showed better scalability in I/O bound applications for shared memory benchmarks. We incorporated the support for ARM in the MPJ‐Express runtime and performed comparative analysis of two widely used message passing libraries. We obtained similar results for network bandwidth, large‐scale application scaling, floating‐point performance, and energy‐efficiency for clusters in message passing evaluations (NBP and Gadget 2 with MPJ‐Express and MPICH). Our findings can be used to evaluate the energy efficiency of ARM‐based clusters for server workloads and scientific workloads and to provide a guideline for building energy‐efficient HPC clusters. Copyright © 2015 John Wiley & Sons, Ltd.     

计算密集型大流量数据的接力计算与动态分流处理

针对当前大流量数据计算速度慢、服务器端计算压力大等问题,提出一套计算密集型大流量数据的接力计算与动态分流处理模型。首先,在分布式环境下,使用内存型数据存储技术确定计算任务的运算量与复杂等级,同时利用节点资源能力对节点进行排序;然后,动态分配任务到不同节点进行并行计算,并采用一种接力处理模式完成计算任务的分解,以有效保证高流量复杂运算任务的性能和精度要求。通过分析对比,可知在万级以上数据量的情况下,多个节点比单个节点的运行时间更短、计算速度更快;而且,将该模型应用于实际时,发现它不仅能在高并发场景下减少运行时间,而且也能节省更多计算资源。     

嵌入式通讯平台的设计与实现

介绍了一个基于客户/服务器模式下的嵌入式通讯平台的设计原理,分析了它的软硬件组成、Socket通信流程和串口类的封装,阐述了在Delphi环境下COM(component object model)的实现原理,以及如何利用套接字控件完成COM服务器和COM客户端之间的数据传递,此外,结合实例说明了串口通信的流程.     

Efficient distributed SAT and SAT-based distributed Bounded Model Checking

SAT-based Bounded Model Checking (BMC), though a robust and scalable verification approach, still is computationally intensive, requiring large memory and time. Even with the recent development of improved SAT solvers, the memory limitation of a single server rather than time can become a bottleneck for doing deeper BMC search for large designs. Distributing computing requirements of BMC over a network of workstations can overcome the memory limitation of a single server, albeit at increased communication cost. In this paper, we present (a) a method for distributed SAT over a network of workstations using a Master/Client model where each Client workstation has an exclusive partition of the SAT problem and uses knowledge of partition topology to communicate with other Clients, (b) a method for distributing SAT-based BMC using the distributed SAT. For the sake of scalability, at no point in the BMC computation does a single workstation have all the information. We experimented on a network of heterogeneous workstations interconnected with a standard Ethernet LAN. To illustrate, on an industrial design with ∼13 K FFs and ∼0.5 million gates, the non-distributed BMC on a single workstation (with 4 GB memory) ran out of memory after reaching a depth of 120; on the other hand, our SAT-based distributed BMC over 5 similar workstations was able to go up to 323 steps with a communication overhead of only 30%.     

面向瘦客户端的分布式动态二进制翻译系统

传统的动态二进制翻译系统不适合直接用于瘦客户端,因为瘦客户端（如手机等）大多存在资源受限的问题,而动态二进制翻译过程会消耗较多的计算和内存资源。针对上述问题,提出一个适用于瘦客户端的分布式动态二进制翻译系统,用远程服务器完成二进制翻译,客户端只要执行翻译好后的代码即可。CPUSPEC2000的实验结果表明,在瘦客户端上使用该系统相对于使用传统的动态二进制翻译器可以带来更高的性能和更小的开销。     

因特网上基于节点角色的计算资源共享平台——RB-CRSP

提出了因特网上基于节点角色的计算资源共享平台——RB-CRSP。设计时充分考虑节点的角色性和功能性,把因特网上的网络资源按照角色划分为服务器端节点、协调节点、工作机节点与客户机节点四类实体,通过配合RB-CRSP的应用编程模式,完成并行分布式计算。分析了RB-CRSP中的自适应资源调度策略,该策略考虑了节点的硬件信息与可信誉机制,实现了平台的负载均衡性;在动态的因特网环境下,利用面向工作机的容错方式保证了平台的可靠性。案例程序选择了典型的并行BenchMark程序：N皇后问题,测试结果表明,RB-CRSP可以方便聚集异构环境下的空闲计算资源,平台的性能与机器硬件条件和可靠性密切相关。     

基于无线传感器网络的移动数据库体系结构的研究

无线传感器网络数据需要数据库的管理,用户有随时随地查询数据的要求,提出了一种基于无线传感器网络的移动数据库,它为三层体系结构,介绍了无线传感器网络普通节点层、汇聚节点处移动数据库服务器端和移动客户端这三层的功能组成.     

On private Hamming distance computation

Finding similarities between two datasets is an important task in many research areas, particularly those of data mining, information retrieval, cloud computing, and biometrics. However, maintaining data protection and privacy while enabling similarity measurements has become a priority for data owners in recent years. In this paper, we study the design of an efficient and secure protocol to facilitate the Hamming distance computation between two semi-honest parties (a client and a server). In our protocol design, both parties are constrained to ensure that no extra information will be revealed other than the computed result (privacy is protected) and further, the output of the protocol is according to the prescribed functionality (correctness is guaranteed). In order to achieve these requirements, we utilize a multiplicative homomorphic cryptosystem and include chaff data into the computation. Two experimental results in this paper demonstrate the performance of both the client and the server.     

The Distributed Workflow Management System — FlowAgent

While mainframe or 2-tier client/server system have serious problems in flexibility and scalability for the large-scale business processes,3-tier client/server architecture and object-oriented system modeling which construct business process on service components seem to bring software system some scalability.As enabling infrastructure for object-oriented methodology,distributed WFMS(Workflow Management System)can flexibly describe business rules among autonomous service tasks,and support scalability of large-scale business process.But current distributed WFMS still have difficulty to manage a large number of distributed tasks,the Multi-Task DOmain‘architecture of FlowAgent will try to solve this problem,and bring a dynamic and distributed environment for task-scheduling.