《分布式系统》全册配套完整教学课件3.pptx

1、分布式系统全册配套完整分布式系统全册配套完整教学课件教学课件3分布式系统课程课程范围教材共教材共1313章，我们课程介绍章，我们课程介绍1212章；章；第一章：引言第一章：引言第二章第二章第九章：原理部分第九章：原理部分第十章第十章第十三章：范例第十三章：范例基本内容Chapter 1 IntroductionChapter 2 Communication(RPC/RMI/MOM)Chapter 3 Distributed Computing ParadigmChapter 4 Processes(虚拟化；代码迁移的模型；进程虚拟化；代码迁移的模型；进程/处理机的分配方法处理机的分配方法)Ch

2、apter 5 NamingChapter 6 SynchronizationChapter 7 Consistency and Replication(DATA-CENTRIC/CLIENT-CENTRIC CONSISTENCY MODELS)Chapter 8 Fault ToleranceChapter 9 SecurityChapter 10 Distributed File SystemsChapter 11 Distributed Object-based SystemsChapter 12 Distributed Web-Based Systems 基本要求基本要求 基本概念基

3、本概念; 基本原理基本原理; 应用范例应用范例;IntroductionChapter 11.1 Definition of a Distributed System A distributed system is a collection of A distributed system is a collection of independent computers that appears to its independent computers that appears to its users as a single coherent system.users as a single

4、coherent system. 硬件角度：各个计算机是自治的，通过网络互联；硬件角度：各个计算机是自治的，通过网络互联； 软件角度：用户看到的是一台逻辑计算机。软件角度：用户看到的是一台逻辑计算机。（互联、协作、单一视图）（互联、协作、单一视图） 分布式计算是指在分布式系统上执分布式计算是指在分布式系统上执行的计算。诸如网络服务和网络应用等。行的计算。诸如网络服务和网络应用等。像像WWWWWW、EmailEmail、FTPFTP、企业计算、聊天室、企业计算、聊天室和网络游戏等。和网络游戏等。 （并发，并行，分布）（并发，并行，分布） 1.1 Concept of a Distributed

5、Computing 分布式计算的最早形态出现在分布式计算的最早形态出现在8080年代末年代末的的IntelIntel公司，他们利用局域网上工作站的公司，他们利用局域网上工作站的空闲时间为芯片设计进行计算。空闲时间为芯片设计进行计算。 随着随着InternetInternet的迅速发展和普及，分布的迅速发展和普及，分布式计算的研究在式计算的研究在9090年代后达到了高潮。互联年代后达到了高潮。互联网上的应用本身就是一种分布式计算应用。网上的应用本身就是一种分布式计算应用。1.1 Concept of a Distributed Computing 产生的背景：产生的背景：应用驱动和技术支撑应用驱

6、动和技术支撑. . 一、应用驱动一、应用驱动 1 1、客观世界的组织活动本身具有分布客观世界的组织活动本身具有分布特性，例如：制造、销售、银行、仓储特性，例如：制造、销售、银行、仓储以及互联网世界等以及互联网世界等业务分布。业务分布。 2 2、性价比高、资源共享、坚定性高和、性价比高、资源共享、坚定性高和可伸缩性。可伸缩性。二、技术支撑二、技术支撑 20 20世纪世纪8080年代中期，两个技术的进步年代中期，两个技术的进步在硬件上为分布式系统提供了基础：在硬件上为分布式系统提供了基础： 1 1、微处理机的出现（价格低廉）。、微处理机的出现（价格低廉）。 2 2、高速网络的出现。、高速网络的出现

7、。互联网平台的特征互联网平台的特征开放性开放性多变性多变性动态性动态性n无统一控制的无统一控制的“真真”分布性分布性n节点的高度自治性和不可预测性节点的高度自治性和不可预测性n节点链接的开放性和灵活性节点链接的开放性和灵活性n网络连接方式的多样性网络连接方式的多样性n使用方式的个性化和多样性使用方式的个性化和多样性 n人、设备和软件的多重异构性人、设备和软件的多重异构性 大型机大型机-终端终端客户机客户机-服务器服务器微机微机-局域网局域网互联网互联网按需按需/普适计算普适计算第一阶段第一阶段第二阶段第二阶段第三阶段第三阶段第四阶段第四阶段初期普及阶段初期普及阶段 更多专家以更多专家以及一般用

8、户开始及一般用户开始使用，用户要很使用，用户要很好地使用需要深好地使用需要深入了解计算机知入了解计算机知识。识。 对对国国民民经经济济和和社社会会发发展展的的影影响响目前阶段目前阶段专家阶段专家阶段 计算机仅供少计算机仅供少数专家和专业人员数专家和专业人员使用，社会公众很使用，社会公众很难用上。难用上。 公众认识阶段公众认识阶段 因特网和因特网和Web时代，信息技术时代，信息技术已在公众中流行已在公众中流行起来，但用户仍起来，但用户仍然需要知道一些然需要知道一些计算机和信息技计算机和信息技术的知识。术的知识。 广泛普及阶段广泛普及阶段 用户已经看用户已经看不见技术，也不不见技术，也不需要知道技

9、术，需要知道技术，只要看得到技术只要看得到技术带来的好处。带来的好处。其他其他: 云计算云计算,物物联网等联网等.时间时间计算环境演化计算环境演化M-to-1 1-to-1 1-to-M专业人员专业人员 有专业要求的人员有专业要求的人员 任何人员任何人员Mainframe PCs/Handhelds LAN Internet IoT.Calculations Information Services 计算为中心计算为中心 信息为中心信息为中心 用户为中心用户为中心计算模型：计算模型：封闭可控封闭可控 开放不确定开放不确定Gartner：2011十大战略技术十大战略技术 云计算居首云计算居首 计

10、算模式大爆炸计算模式大爆炸系统软件的作用系统软件的作用 图灵机模型图灵机模型应用系统应用系统 计算机硬件计算机硬件/网络网络 系统软件系统软件操作系统：主机操作系统：主机OS、桌面、桌面OS、网络、网络OS、中间件系统、中间件系统、WebOS、VMM、网构网构编程方面：机器语言、汇编语言、面向编程方面：机器语言、汇编语言、面向过程、面向对象、面向构件、过程、面向对象、面向构件、Eclipse、Agent.其他其他计算为中心计算为中心信息为中心信息为中心用户为中心用户为中心GAP实实虚虚不变不变/变化的地方变化的地方 无论计算环境如何变化，系统软件的2个基础作用不变：u运行时支撑；u设计时支撑；

11、用户体验已经作为系统软件成功与否的关键因素：u运行支撑环境：高效能、高可靠、高可用、可信、低成本、低能耗、界面；u设计支撑：抽象层次越来越高；例1：系统由多个工作站（终端）和1个共享处理机池(pool of processor)经网络联结组成，系统为用户提供单一的文件系统，空闲的工作站和处理机动态分配。 这个从系统整体上看以及运行起来看都像一个典型的单处理机分时系统，实际上是一个分布式系统（分布并行计算）。 例2：一个在世界各地有数百个分支机构的大银行。每个分支机构有一台主计算机存储当地帐目和处理本地事务。此外，每台计算机还能与其他分支机构的计算机及总部的计算机对话。 如果交易不管顾客和帐目在

12、哪里都能够进行，而且用户也不会感到当前这个系统与被替代的老的集中式主机有何不同，那么这个系统也被认为是一个分布式系统（分布式事务处理）。 例3：分布式文档处理，如WWW系统。 通过URL，实现对分布文档以位置透明的方式访问，分布式文档处理。 分布式计算的主要缺点：多点故障：一台（条）或多台多点故障：一台（条）或多台（条）（条）计算机（网计算机（网络链路）的故障会导致分布式系统出现问题。络链路）的故障会导致分布式系统出现问题。安全问题：分散式管理使安全策略的实现和增强安全问题：分散式管理使安全策略的实现和增强变得更为困难。变得更为困难。 分布式系统的实现方式分布式系统的实现方式: :低级编程低级

13、编程; ;操作系统操作系统( (分布式分布式););中间件技术中间件技术; ;低级编程：低级编程： 利用网络协议和操作系统等提供的低级服务来构利用网络协议和操作系统等提供的低级服务来构造各种分布式应用系统。开发效率低，软件的质造各种分布式应用系统。开发效率低，软件的质量难以保证。量难以保证。操作系统操作系统( (分布式分布式) )： 兼容现存软件适应开放异构性适应应用多样兼容现存软件适应开放异构性适应应用多样性等方面存在不足。性等方面存在不足。中间件技术：中间件技术： 对广泛的一类问题具有较好的适用性。它可支持对广泛的一类问题具有较好的适用性。它可支持广泛一类应用软件的高效和高质量的开发。广泛

14、一类应用软件的高效和高质量的开发。1.1A distributed system organized as middleware.Note that the middleware layer extends over multiple machines.1.2 GOALS: 1. Connecting Users and Resources: to make it easy for users to access remote resources, and to share them with other users in a controlled way. 2. Transparency:

15、to hide the fact that its processes and resources are physically distributed across multiple computers. 3. Openness: to offers services according to standard rule that describe the syntax and semantics of those services.(e.g. IDL-Interface Definition Language) 4. Scalability: in size, geographically

16、, and administrativelyTransparency in a Distributed SystemDifferent forms of transparency in a distributed system.TransparencyDescriptionAccessHide differences in data representation and how a resource is accessedLocationHide where a resource is locatedMigration Hide that a resource may move to anot

17、her locationRelocationHide that a resource may be moved to another location while in useReplicationHide that a resource is replicatedConcurrencyHide that a resource may be shared by several competitive usersFailureHide the failure and recovery of a resourcePersistenceHide whether a (software) resour

18、ce is in memory or on diskScalability ProblemsExamples of scalability limitations.ConceptExampleCentralized servicesA single server for all usersCentralized dataA single on-line telephone bookCentralized algorithmsDoing routing based on complete information There are basically only three techniques

19、for scaling:1. Hiding communication latencies (asynchronous communication)2. Distribution(e.g. DNS)3. Replication(leads to consistency problems)Scaling Techniques (1)1.4The difference between letting:a) a server orb) a client check forms as they are being filledScaling Techniques (2)1.5An example of

20、 dividing the DNS name space into zones.1.3 Hardware Concepts计算机系统的分类（按Flynn的分类）： 1、SISD（Single Instruction stream，Single Data stream）单处理机计算机。 2、SIMD（Single Instruction stream， Multiple Data stream），一些超级计算机。 3、MISD（Multiple Instruction stream，Single Data stream）。此类型计算机有多条指令流，一条数据流。目前计算机中没有属于这一类。 4、M

21、IMD（Multiple Instruction stream， Multiple Data stream），分布式系统属于此类型。计算机系统的分类（续）： 紧耦合型(tightly coupled)系统计算机之间发送信息的时延很短、数据传输速率高。 松耦合型(loosely coupled) 系统机器间信息传送延迟大，数据传输速率也低。1.6Different basic organizations and memories in distributed computer systemsMultiprocessors (1)A bus-based multiprocessor.1.7存储器相

22、关(Coherent)Multiprocessors (2)1.8交叉开关 交换网络Homogeneous Multicomputer Systems1-9GridHypercubeHeterogeneous Multicomputer Systemsa.基于总线 b.基于交换并行及分布式计算机系统分类：并行分布式计算机多处理机(共享存储器)多计算机(私有存储器)总线开关总线开关紧耦合松耦合MIMD sequent 超级计算机 LAN工作站 超立方体 Encor RP3 Transputer交换交换基于总线: 广播方式; 基于交换: 路由方式1.4 Software Concepts软件系统：

23、软件系统：紧耦合型紧耦合型( (tightly coupled)tightly coupled)系统系统单系统映象单系统映象（single-system imagesingle-system image）。往往称为分布式。往往称为分布式操作系统操作系统. .松耦合型松耦合型( (loosely coupled)loosely coupled) 系统系统松耦合的软松耦合的软件允许分布式系统的机器和用户基本上各自独件允许分布式系统的机器和用户基本上各自独立，但是也在必要的情况下进行一定程度的相立，但是也在必要的情况下进行一定程度的相互作用。往往称为网络操作系统互作用。往往称为网络操作系统. . A

24、n overview between DOS (Distributed Operating Systems) NOS (Network Operating Systems) MiddlewareSystemDescriptionMain GoalDOSTightly-coupled operating system for multi-processors and homogeneous multicomputersHide and manage hardware resourcesNOSLoosely-coupled operating system for heterogeneous mu

25、lticomputers (LAN and WAN)Offer local services to remote clientsMiddlewareAdditional layer atop of NOS implementing general-purpose servicesProvide distribution transparencyDistributed Operating Systems(1. Uniprocessor Operating Systems) DOS在功能上同UOS2. Multiprocessor Operating Systems ?3. Multicomput

26、er Operating Systems Uniprocessor Operating Systems 单机操作系统可以有多种结构实现，目的是管理整个计算机系统的资源，并为用户提供使用上的方便。 操作系统的结构： 模块结构； 层次结构； 微内核结构； 面向对象等。Uniprocessor Operating Systems Separating applications from operating system code through a microkernel.1.11Multiprocessor Operating Systems (1) Multiprocessor Operatin

27、g Systems aim to support high performance through multiple CPUs. An important goal is to make the number of CPUs transparent to the application. Achieving such transparency is relatively easy because the communication between different parts of application uses the same primitives as those in multit

28、asking uniprocessor operating systems. Two important primitives are semaphores and monitors (只需保护数据不在同一时刻受到多个访问)Multiprocessor Operating Systems (1)A monitor to protect an integer against concurrent access.monitor Counter private:int count = 0;public: int value() return count; void incr () count = c

29、ount + 1; void decr() count = count 1;Multiprocessor Operating Systems (2) A monitor to protect an integer against concurrent access, but blocking a process.monitor Counter private: int count = 0; int blocked_procs = 0; condition unblocked;public: int value () return count; void incr () if (blocked_

30、procs = 0) count = count + 1; else signal (unblocked); void decr() if (count =0) blocked_procs = blocked_procs + 1; wait (unblocked); blocked_procs = blocked_procs 1; else count = count 1; Multicomputer Operating Systems (1)General structure of a multicomputer operating system(through message passin

31、g)松耦合硬件上的紧耦合软件，系统目标是使用户产生一个视觉：整个计算机网络是一个分时系统，而不是一个互不相同的机器的集合。(没有共享存储, 只能消息传递) 1.14Multicomputer Operating Systems (2)Alternatives for blocking and buffering in message passing. (four possibly synchronization points. if the operating system blocks a sender until messages arrive at either S3 or S4, it

32、 must guarantee reliable communication. more complex)1.15Multicomputer Operating Systems (3)Relation between blocking, buffering, and reliable communications.Synchronization pointSend bufferReliable comm. guaranteed?Block sender until buffer not full(满时阻塞发送进程满时阻塞发送进程)YesNot necessaryBlock sender unt

33、il message sentNoNot necessaryBlock sender until message receivedNoNecessaryBlock sender until message deliveredNoNecessary同步点与消息传递语义理解(消息可靠性)Distributed Shared Memory Systems (1)a)Pages of address space distributed among four machinesb)Situation after CPU 1 references page 10c)Situation if page 10

34、is read only and replication is usedWhen a processor references an address that is not present locally, a trap occurs, and the operating system fetches the page containing the address and restarts the faulting instruction.Distributed Shared Memory Systems (2)False sharing of a page between two indep

35、endent processes.1.18要设计高效的DSM, 页的大小设置是一个问题? 太小: 可能中断多,传送次数多. 太大:也可能传送次数多. 例如:Network Operating System (1)General structure of a network operating system.松耦合硬件上的松耦合软件(底层硬件和Kernel可以不同) 1-19Network Operating System (2) 每个用户都有自己专用的工作站（有盘或无盘）。但是它一定有自己的操作系统。所有的命令通常在本地运行。非透明方式使用，例如： rlogin machine rcp mac

36、hine1 : file1 machine2 : file2 （机器的选择完全由人工操作完成） Network Operating System (2)Two clients and a server in a network operating system.(提供一个全局文件系统的方法: 文件服务器)1-20Network Operating System (3)Different clients may mount the servers in different places.缺点: 缺乏透明性1.21Positioning Middleware A distributed opera

37、ting system is not intended to handle a collection of independent computers.(异构) A network operating system does not provide a view of a single coherent system.Positioning Middleware The solution is to be found in an additional layer of software that is used in network operating systems to more or l

38、ess hide the heterogeneity of the collection of underlying platforms but also to improve distribution transparency-middlewarePositioning MiddlewareGeneral structure of a distributed system as middleware.1-22Middleware ModelsTo make development and integration of distributed applications as simple as

39、 possible, most middleware is based on some model, or paradigm, for describing distribution and communication.Some models are as follows: based on distributed file system, based on RPCsRemote Procedure Calls, based on distributed objects, based on distributed documents, Middleware Services为了力图实现访问透明

40、性,There are a number of services common to many middle systems: Naming Persistence Distributed transaction Middleware and Openness 为保证开放性/互操作性: 采用相同的中间件协议和中间件接口.1.23Comparison between SystemsItemDistributed OSNetwork OSMiddleware-based OSMultiproc.Multicomp.Degree of transparencyVery HighHighLowHigh

41、Same OS on all nodesYesYesNoNoNumber of copies of OS1NNNBasis for communicationShared memoryMessagesFilesModel specificResource managementGlobal, centralGlobal, distributedPer nodePer nodeScalabilityNoModeratelyYesVariesOpennessClosedClosedOpenOpenDistributed Computing ParadigmChapter 22.1 Paradigm

42、and Abstractionu Important characteristics that distinguish distributed Important characteristics that distinguish distributed applications from conventional applications which run on a applications from conventional applications which run on a single machine: single machine: Interprocess communicat

43、ion: A distributed application requires the participation of two or more independent entities (processes). To do so, the processes must have the ability to exchange data among themselves.(多方参与多方参与) Event synchronization: In a distributed application, the sending and receiving of data among the parti

44、cipants of a distributed application must be synchronized.2.1 Paradigm and AbstractionParadigm: Paradigm means “a pattern, example, or model.” In the study of any subject of great complexity, it is useful to identify the basic patterns or models, and classify the detail according to these models. 一个

45、用于说明如何完成某项特定任务的抽象模型。2.1 Paradigm and AbstractionAbstractions:n Arguably the most fundamental concept in computer science, abstraction is the idea of detail hiding. We often use abstraction when it is not necessary to know the exact details of how something works or is represented, because we can sti

46、ll make use of it in its simplified form. Getting involved with the detail often tends to obscure what we are trying to understand, rather than illuminate it.(太细节的东西会影响对主要问题的理解)n Abstraction plays a very important role in programming because we often want to model, in software, simplified versions o

47、f things that exist in the real world without having to build the real things.(编程就是对所关注事情的抽象)n In software engineering, abstraction is realized with the provision of tools or facilities which allow software to be built without the developer having to be cognizant of some of the underlying complexiti

48、es.(工具和设施提供抽象)n 科研过程更是如此.2.1 Overview of presented Paradigms Message passing Remote Procedure Call Client-server Peer-to-Peer Message system: Point-to-point; Publish/Subscribe Distributed objects: Remote method invocation Network services Object Request Broker Object space Component Based Technologi

49、es Mobile agents Collaborative applicationsMessage passing Remote Procedure Call Client-server Peer-to-Peer Message system: p Point-to-point; p Publish/Subscribe Distributed objects:p Remote method invocation p Network servicesp Object Request Broker p Object space p Component Based Technologies Mob

50、ile agents Collaborative applications2.2 The Message Passing Paradigm2.2 The Message Passing Paradigm Message passing is the most fundamental paradigm for distributed applications. A process sends a message representing a request. The message is delivered to a receiver, which processes the request,