分布式系统：概念与设计（第五版）

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"分布式系统——概念与设计，第五版" 分布式系统是计算机科学中的一个重要领域，涉及多个相互协作的计算设备，共同完成一项任务或提供服务。本书《分布式系统：概念与设计》由George Coulouris、Jean Dollimore、Tim Kindberg和Gordon Blair等人编写，是该领域的经典教材，现在更新到了第五版。分布式系统的概念涵盖了许多关键主题，包括但不限于： 1. **并发控制**：在分布式系统中，多台计算机可能同时处理同一数据，需要有效的并发控制策略以避免数据不一致性和死锁问题。 2. **容错**：由于网络的不可靠性，节点可能会失败，因此分布式系统必须设计成容错的，能够从硬件或软件故障中恢复。 3. **分布式一致性**：确保所有节点看到的数据是一致的，如通过Paxos、Raft等一致性算法实现。 4. **分布式协调**：通过如Zookeeper、Chubby等协调服务，管理分布式环境中的命名、配置、同步和锁定。 5. **网络通信**：使用套接字编程、RPC（远程过程调用）和消息传递协议（如AMQP、MQTT）实现节点间的高效通信。 6. **负载均衡**：有效地分配任务到不同的计算资源，以优化性能和响应时间。 7. **分布式数据库**：如ACID（原子性、一致性、隔离性、持久性）和BASE（基本可用、软状态、最终一致性）原则，以及NoSQL数据库的设计。 8. **安全性与隐私**：保护数据安全，防止未授权访问，实现身份验证和加密通信。 9. **云计算与微服务**：分布式系统在云计算环境中的应用，以及微服务架构如何促进可伸缩性和独立部署。 10. **物联网(IoT)**：分布式系统在连接大量传感器和设备的环境中的应用，如数据收集和处理。 11. **移动计算**：考虑到移动设备的特性（如电池寿命、网络连接不稳定），设计适应性的分布式解决方案。 12. **分布式文件系统**：如Hadoop DFS和Google File System，它们允许大规模数据的分布式存储和处理。本书第五版可能会涵盖近年来的新进展，如边缘计算、区块链技术、容器化和Serverless架构等。作者们通过丰富的实例和深入的分析，帮助读者理解这些复杂概念并学会设计和实现自己的分布式系统。《分布式系统：概念与设计》为学习和理解分布式系统的复杂性和挑战提供了全面的指导，适合计算机科学专业的学生以及希望深入研究分布式系统的专业人士阅读。

XIV PREFACE

only on the Web. They can be looked up in the reference list at the end of the book, but

the full URLs are given only in an online version of the reference list at the book’s web

site, www.cdk5.net/refs

where they take the form of clickable links. Both versions of the

reference list include a more detailed explanation of this scheme.

Changes relative to the fourth edition

Before embarking on the writing of this new edition, we carried out a survey of teachers

who used the fourth edition. From the results, we identified the new material required

and a number of changes to be made. In addition, we recognized the increasing diversity

of distributed systems, particularly in terms of the range of architectural approaches

available to distributed systems developers today. This required significant changes to

the book, especially in the earlier (foundational) chapters.

Overall, this led to our writing three entirely new chapters, making substantial

changes to a number of other chapters and making numerous insertions throughout the

book to fold in new material. Many of the chapters have been changed to reflect new

information that has become available about the systems described. These changes are

summarized in the table below. To help teachers who have used the fourth edition,

wherever possible we have preserved the structure adopted from the previous edition.

Where material has been removed, we have placed this on our companion web site

together with material removed from previous editions. This includes the case studies

on ATM, interprocess communication in UNIX, CORBA (a shortened version of which

remains in Chapter 8), the Jini distributed events specification and Grid middleware

(featuring OGSA and the Globus toolkit), as well as the chapter on distributed shared

memory (a brief summary of which is now included in Chapter 6).

Some of the chapters in the book, such as the new chapter on indirect

communication (Chapter 6), cover a lot of material. Teachers may elect to cover the

broad spectrum before choosing two or three techniques to examine in more detail (for

example, group communication, given its foundational role, and publish-subscribe or

message queues, given their prevalence in commercial distributed systems).

The chapter ordering has been changed to accommodate the new material and to

reflect changes in the relative importance of certain topics. For a full understanding of

some topics readers may find it necessary to follow a forward reference. For example,

there is material in Chapter 9 on XML security techniques that will make better sense

once the sections that it references in Chapter 11 Security have been absorbed.

Acknowledgements

We are very grateful to the following teachers who participated in our survey: Guohong

Cao, Jose Fortes, Bahram Khalili, George Blank, Jinsong Ouyang, JoAnne Holliday,

George K. Thiruvathukal, Joel Wein, Tao Xie and Xiaobo Zhou.

We would like to thank the following people who reviewed the new chapters or

provided other substantial help: Rob Allen, Roberto Baldoni, John Bates, Tom Berson,

Lynne Blair, Geoff Coulson, Paul Grace, Andrew Herbert, David Hutchison, Laurent

Mathy, Rajiv Ramdhany, Richard Sharp, Jean-Bernard Stefani, Rip Sohan, Francois

XVI PREFACE

Taiani, Peter Triantafillou, Gareth Tyson and the late Sir Maurice Wilkes. We would

also like to thank the staff at Google who provided insights into the design rationale for

Google Infrastructure, namely: Mike Burrows, Tushar Chandra, Walfredo Cirne, Jeff

Dean, Sanjay Ghemawat, Andrea Kirmse and John Reumann.

Our copy editor, Rachel Head also provided outstanding support.

Web site

As before, we continue to maintain a web site with a wide range of material designed to

assist teachers and readers. This web site can be accessed via the URL:

www.cdk5.net

The web site includes:

Instructor’s Guide: We provide supporting material for teachers comprising:

• complete artwork of the book available as PowerPoint files;

• chapter-by-chapter teaching hints;

• solutions to the exercises, protected by a password available only to teachers.

Reference list: The list of references that can be found at the end of the book is replicated

at the web site. The web version of the reference list includes active links for material

that is available online.

Errata list: A list of known errors in the book is maintained, with corrections. The errors

will be corrected when new impressions are printed and a separate errata list will be

provided for each impression. (Readers are encouraged to report any apparent errors

they encounter to the email address below.)

Supplementary material: We maintain a set of supplementary material for each chapter.

This consists of source code for the programs in the book and relevant reading material

that was present in previous editions of the book but was removed for reasons of space.

References to this supplementary material appear in the book with links such as

www.cdk5.net/ipc

(the URL for supplementary material relating to the Interprocess

Communication chapter). Two entire chapters from the 4th edition are not present in this

one; they can be accessed at the URLs:

CORBA Case Study www.cdk5.net/corba

Distributed Shared Memory www.cdk5.net/dsm

George Coulouris

Jean Dollimore

Tim Kindberg

Gordon Blair

London, Bristol and Lancaster, 2011

authors@cdk5.net

2 CHAPTER 1 CHARACTERIZATION OF DISTRIBUTED SYSTEMS

1.1 Introduction

Networks of computers are everywhere. The Internet is one, as are the many networks

of which it is composed. Mobile phone networks, corporate networks, factory networks,

campus networks, home networks, in-car networks – all of these, both separately and in

combination, share the essential characteristics that make them relevant subjects for

study under the heading distributed systems. In this book we aim to explain the

characteristics of networked computers that impact system designers and implementors

and to present the main concepts and techniques that have been developed to help in the

tasks of designing and implementing systems that are based on them.

We define a distributed system as one in which hardware or software components

located at networked computers communicate and coordinate their actions only by

passing messages. This simple definition covers the entire range of systems in which

networked computers can usefully be deployed.

Computers that are connected by a network may be spatially separated by any

distance. They may be on separate continents, in the same building or in the same room.

Our definition of distributed systems has the following significant consequences:

Concurrency: In a network of computers, concurrent program execution is the norm.

I can do my work on my computer while you do your work on yours, sharing

resources such as web pages or files when necessary. The capacity of the system to

handle shared resources can be increased by adding more resources (for example.

computers) to the network. We will describe ways in which this extra capacity can be

usefully deployed at many points in this book. The coordination of concurrently

executing programs that share resources is also an important and recurring topic.

No global clock: When programs need to cooperate they coordinate their actions by

exchanging messages. Close coordination often depends on a shared idea of the time

at which the programs’ actions occur. But it turns out that there are limits to the

accuracy with which the computers in a network can synchronize their clocks – there

is no single global notion of the correct time. This is a direct consequence of the fact

that the only communication is by sending messages through a network. Examples of

these timing problems and solutions to them will be described in Chapter 14.

Independent failures: All computer systems can fail, and it is the responsibility of

system designers to plan for the consequences of possible failures. Distributed systems

can fail in new ways. Faults in the network result in the isolation of the computers that

are connected to it, but that doesn’t mean that they stop running. In fact, the programs

on them may not be able to detect whether the network has failed or has become

unusually slow. Similarly, the failure of a computer, or the unexpected termination of

a program somewhere in the system (a crash), is not immediately made known to the

other components with which it communicates. Each component of the system can fail

independently, leaving the others still running. The consequences of this characteristic

of distributed systems will be a recurring theme throughout the book.

The prime motivation for constructing and using distributed systems stems from a desire

to share resources. The term ‘resource’ is a rather abstract one, but it best characterizes

the range of things that can usefully be shared in a networked computer system. It

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