分布计算系统.ppt

1、分布计算系统,DISTRIBUTED SYSTEMS Principles and Paradigms （分布式系统-原理与范型） Andrew S.Tanenbaum Maarten van Steen 著 杨剑锋 等译 清华大学出版社,主讲教师： 袁道华 教授,授课内容,分布式系统绪论 分布式系统模型 分布式系统中的通信 分布式系统中的进程 分布式系统中的复制和一致性 分布式系统中的容错性 分布式系统中的负载分配 分布式程序设计 分布式数据库系统 分布式对象计算系统,多数计算机网络的利用率都很低，网络结点经常处于闲置状态。 发掘计算机网络中潜在的并行处理能力，或利用计算机（WorkStat

2、ion，高档PC，SMP，HPC，）网络进行网络并行计算，是近年来分布式系统的一个重要的研究和应用领域。 - Network Of Workstation - Cluster Of Workstation - Grid Computing,分布式系统绪论,Distributed Systems,A distributed system is: A collection of independent computers that appears to its users as a single coherent system. 分布式系统是一组逻辑和物理上互联的处理单元的集合。其实施对资源的系统

3、范围的分散控制，以达到对应用程序的协同执行。,Distributed Systems, A distributed system is a collection of processors that do not share memory or a clock. Each processor has its own local memory. The processors in the system are connected through a communication network. A distributed system provides user access to variou

4、s system resources. Access to a shared resource allows: - Computation speed-up - Increased data availability - Enhanced reliability,分布式系统的特点, 资源分散性 结构模块性 控制自治性 工作并行性 运行坚定性 系统透明性,分布式系统应具备以下基本功能,通信 系统提供某种通信手段，使得运行于不同计算机上的用户程序可通过通信来交换数据。 资源共享 系统提供访问它机资源的功能，使得在终端操作的用户或在某台计算机上运行的用户程序可以访问或使用位于它机的资源。 并行运算

5、系统提供某种程序设计语言，使得用户可以用来编写分布式程序，即一个分布于若干台计算机上的程序。 健壮性 即系统对故障（部分失效）的免疫力（容错能力）。当系统中有一台甚至数台计算机发生故障时，系统在正常运行的那些计算机的支持下仍可继续工作。,Distributed Computing System,Examples,Some examples of distributed systems - Department computing cluster - Corporate systems Application examples - Email, News - Multimedia informa

6、tion systems video conferencing - Airline reservation system - Banking system What is the most used distributed system? - World Wide Web （广义地讲： The Internet, an intranet, mobile and ubiquitous computing are all examples of distributed systems）,分布式系统实例,考虑一个大学的工作站网络 除了每个用户的个人工作站外，在机房里面可能还有一个处理器池，它们不分配

7、给特定的用户，而是动态地按需分配。那样的系统可能有一个单一的文件系统，所有文件可以由所有机器以相同的方式并使用相同的路径名进行访问。进一步，当一个用户敲入一条命令的时候，系统能够寻找最好的地方执行这条命令，可能是在用户自己的工作站，也可能是在一台属于别人的空闲工作站，或者是在机房里面未分配的一个处理器上。如果系统是作为一个整体看，并且在行为上像是一个典型的单处理器分时系统，那么它是一个合格的分布式系统。,分布式系统实例,2. 考虑一个大型银行系统 它在全世界有数百个分支机构。每一个分支机构有一台主计算机，用以存储本地帐户（accounts）和处理本地事务（transactions）。此外，每台

8、计算机能够与所有其它分支机构的计算机以及在总部的中央计算机进行对话（talk）。如果不论客户或帐户在哪里，都能够对事务进行处理（做交易），并且用户不会注意到本系统与它所替换的老的集中式主架机系统之间的任何差异，那么它也被认为是一个分布式系统。,Distributed vs. Single Systems (分布式系统相对单机系统的优点),Data sharing - Multiple users can access common database, data files, Device /resource sharing - Printers, servers, CPUs, Communic

9、ation - Communication with other machines Flexibility - Spread workload to different & most appropriate machines Extensibility - Add resources and software as needed,Distributed vs. Centralized Systems(分布式系统相对集中式系统的优点),Economics - Microprocessors have better price/performance than mainframes Speed -

10、 A distributed system may have more total computing power than a mainframe (collective power of large number of systems) Inherent distribution - Some applications involve spatially separated machines Reliability - One machines failure need not bring down the system Extensibility - Computers and soft

11、ware can be added incrementally,Distributed Systems vs. Computer Networks,网络操作系统是运行在松耦合硬件上的松耦合的软件。除了共享文件系统外，对用户显而易见的是这个系统包含有许多计算机。每台计算机都运行它自己的操作系统。除了客户/服务器通信必须遵守协议之外，计算机之间基本上没有什么合作。 分布式系统是在网络计算机的集合上运行，但行为却像一个虚拟的单处理机，用户意识不到系统中由多个CPU存在，这种性质称为单一系统映像。目前还没有一个系统能完全满足这一要求。,Transparency in a Distributed Sys

12、tem,Different forms of transparency in a distributed system.,Scalability Problems,Examples of scalability limitations.,Hardware Concepts,Parallel and Distributed Systems,Multiprocessors (fast hw network),Multicomputers (slow hw network),Shared-Memory Multiprocessors,Distributed-Memory Multiprocessor

13、s,UMA,NUMA,tightly coupled,loosely coupled,Homogeneous Multicomputers,Heterogeneous Multicomputers,Network of Workstation,PC Cluster,Workstation Cluster,Distributed Systems,Hardware Concepts (2),1.6,Different basic organizations and memories in distributed computer systems（处理器和存储器的不同组织方式）,（基于交换）,Mul

14、tiprocessors (1),A bus-based multiprocessor.,1.7,Multiprocessors (2),A crossbar switch An omega switching network,1.8,两种交换方式,（多级互连网络）,（交叉开关）,Homogeneous Multicomputer Systems,Grid Hypercube,1-9,Software Concepts,An overview between DOS (Distributed Operating Systems) NOS (Network Operating Systems)

15、Middleware,Uniprocessor Operating Systems,1.11,Microkernel architecture Small kernel user-level servers implement additional functionality Separating applications from operating system code through a microkernel.,Multiprocessor Operating Systems,Like a uniprocessor operating system Manage multiple C

16、PUs transparently to the user Each processor has its own hardware cache Maintain consistency of cached data Shared variable versus message passing,Multicomputer Operating Systems,General structure of a multicomputer operating system,More complex than multiprocessor OS Because communication has to be

17、 through explicit message passing,Multicomputer Operating Systems (2),每个结点都拥有自己的内核，内核中有负责管理本地资源(比如存储器、本地CPU、本地磁盘等)的模块。同时，每个结点还包含一个单独的模块，负责对处理器间通信进行处理，也就是向其他结点发送消息，并从其他结点接收消息。 在每个本地内核上面是一个公共软件层，它实现了操作系统作为支持各种任务并行执行和并发执行的虚拟机的功能。实际上，该层甚至可以提供多处理器计算机的抽象，即提供共享存储器的软件实现。该层中还实现了另外一些功能，例如，向处理器指派任务、屏蔽硬件故障、提供透明

18、存储和常规进程间通信。也可以说，该层具备了一般操作系统应该具有的所有功能。 不提供共享存储器的多计算机操作系统只能向应用程序提供消息传递功能。不幸的是，消息传递原语的语义在不同系统间可能有着巨大的差异。,Distributed Shared Memory Systems (1),Pages of address space distributed among four machines Situation after CPU 1 references page 10 Situation if page 10 is read only and replication is used,Distri

19、buted Shared Memory Systems (2),False sharing of a page between two independent processes.,1.18,将分别属于不同处理器上的两个独立进程的数据放在同一页内，操作系统可能会不断地在这两个处理器间传输该页。,Network Operating System (1),General structure of a network operating system.,1-19,Network Operating System (2),Two clients and a server in a network op

20、erating system.,1-20,Users are aware of multiplicity of machines. Access to resources of various machines is done explicitly by Remote logging into the appropriate remote machine. Transferring data from remote machines to local machines, via the File Transfer Protocol (FTP) mechanism.,Network-Operat

21、ing Systems (3),网络操作系统并不假定底层硬件是同构的，也不认为所有硬件应该作为单个系统集中管理，每个系统都拥有自己的操作系统。 网络操作系统缺乏透明性。,Distributed Operating System,Users not aware of multiplicity of machines. Manages resources in a distributed system Seamlessly and transparently to the user Looks to the user like a centralized OS But operates on mu

22、ltiple independent CPUs Provides transparency Location, migration, concurrency, replication, Presents users with a virtual uniprocessor,Middleware-based Systems,General structure of a distributed system as middleware. (通过在Network OS基础上的Middleware提供部分Distributed OS Services),1-22,What is Middleware,S

23、oftware above the operating system but below the application program Middleware refers to the software that is common to multiple applications and builds on the network transport services to enable ready development of new applications and network services CORBA, DCOM, Java RMI, Grid,Middleware Laye

24、r,Middleware and Openness,In an open middleware-based distributed system, the protocols used by each middleware layer should be the same, as well as the interfaces they offer to applications.,1.23,Comparison between Systems,A comparison between multiprocessor operating systems, multicomputer operating systems, network operating systems, and middleware based distributed systems.,Clients and Servers,General interaction between a client a