深入理解Oracle数据库架构

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"Oracle体系结构是Oracle数据库系统的基础框架，涵盖了数据库的各个组成部分以及它们如何协同工作以存储、管理和检索数据。Oracle体系结构包括多个层次，如物理存储、逻辑结构、进程结构、内存结构等，这些都对数据库的性能、稳定性和可扩展性有着重要影响。专家书籍《Expert Oracle Database Architecture: 9i and 10g Programming Techniques and Solutions》由Thomas Kyte撰写，详细介绍了Oracle 9i和10g版本的相关技术与解决方案。这本书深入解析了Oracle数据库的内部机制，旨在帮助读者理解和优化Oracle环境。在Oracle体系结构中，物理存储层面包括数据文件、控制文件、重做日志文件和口令文件等。数据文件是实际存储数据的地方，控制文件记录了数据库的元数据信息，重做日志文件用于记录事务对数据库所做的所有改变，而口令文件则存储了数据库管理员（DBA）的凭证。逻辑结构则包括表空间、段、区和块等概念。表空间是数据库中数据存储的逻辑单位，由一个或多个数据文件组成。段是由相同类型的数据库对象（如表、索引等）组成的逻辑存储单元。区是分配给段的连续空间，而块是数据库的最小逻辑存储单元，通常包含多行数据及相关的字典信息。在进程结构方面，Oracle数据库运行着多个后台进程，如数据库写入进程（DBWR）、检查点进程（CKPT）、LGWR（日志写入进程）等，它们负责处理I/O操作、维护数据库的一致性以及同步数据和重做日志。此外，还有用户进程，它们与数据库服务器交互执行SQL语句。内存结构主要指系统全局区（SGA）和程序全局区（PGA）。SGA是所有Oracle后台进程共享的一块内存区域，包含数据缓冲区、重做日志缓冲区、共享池和大池等组件。PGA则是每个用户进程的私有内存区域，用于存储会话信息和执行计划。 Oracle数据库还涉及了分布式系统、安全性、备份恢复、性能优化等多个方面。例如，分布式系统允许跨多个数据库实例的数据透明访问；安全性通过权限和角色管理确保数据的访问控制；备份恢复策略确保数据的安全性，如使用RMAN（恢复管理器）进行备份和恢复；性能优化则涉及到索引设计、查询优化、分区技术等，以提高数据库的响应速度和处理能力。《Expert Oracle Database Architecture: 9i and 10g Programming Techniques and Solutions》这本书提供了深入了解Oracle体系结构的宝贵资源，对数据库管理员和开发人员来说具有很高的参考价值。"

About the Technical Reviewers

■JONATHAN LEWIS has been involved in database work for more than 19 years, specializing in

Oracle for the last 16 years, and working as a consultant for the last 12 years. Jonathan is

currently a director of the UK Oracle User Group (UKOUG) and is well known for his many

presentations at the UKOUG conferences and SIGs. He is also renowned for his tutorials and

seminars about the Oracle database engine, which he has held in various countries around

the world.

Jonathan authored the acclaimed book Practical Oracle 8i (Addison-Wesley, ISBN:

0201715848), and he writes regularly for the UKOUG magazine and occasionally for other

publications, including OTN and DBAZine. He also finds time to publish Oracle-related

material on his web site, http://www.jlcomp.demon.co.uk.

■RODERICK MANALAC graduated from the University of California, Berkeley in 1989 with a bach-

elor’s degree in electrical engineering and computer science. He’s been an employee of Oracle

Support Services ever since. Practically all of that time has been spent in assisting external

customers and internal employees (around the globe) gain a better understanding of the sub-

tleties involved with running the Oracle database product on UNIX platforms. Other than

that, he spends way too much time playing video games, watching TV, eating snacks, and will-

ing the San Francisco Giants to win the World Series.

■MICHAEL MÖLLER has been interested in computers since his tenth birthday, approximately

40 years ago. He’s been involved in pretty much everything related to building and running

software systems, as a programmer, design engineer, project manager, and quality assurance

manager. He worked in the computer business in the United States, England, and Denmark

before joining Oracle Denmark ten years ago, where he worked in Support and later in Pre-

mium Support. He has often taught in Oracle Education, even taking the “Oracle Internals”

seminar on a whistle-stop tour of Europe. He spent the last two years of his time with Oracle

working in development in the United States, creating the course materials for advanced

courses, including “Internals on NLS” and “RAC.” Nowadays, Möller is gainfully employed at

Miracle A/S in Denmark with consultancy and education.

■GABE ROMANESCU has a bachelor’s degree in mathematics and works as an independent

Oracle consultant. He discovered relational theory and technologies in 1992 and has found

comfort ever since in the promise of applied logic in the software industry. He mostly benefits

from, and occasionally contributes to, the Ask Tom and OTN forums. He lives in Toronto,

Canada, with his wife, Arina, and their two daughters, Alexandra and Sophia.

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Acknowledgments

Iwould like to thank many people for helping me complete this book.

First, I would like to thank Tony Davis for his work making my work read well. If you enjoy

the flow of the sections, the number of section breaks, and the clarity, then that is probably in

some part due to him. I have worked with Tony writing technical material since the year 2000

and have watched his knowledge of Oracle grow over that time. He now has the ability to not

only “edit” the material, but in many cases “tech edit” it as well. Many of the examples in this

book are there because of him (pointing out that the casual reader was not going to “get it”

without them). This book would not be what it is without him.

Without a technical review team of the caliber I had during the writing of this book, I

would be nervous about the content. Jonathan Lewis, Roderick Manalac, Michael Möller, and

Gabe Romanescu spent many hours poring over the material and verifying it was technically

accurate as well as useful in the real world. I firmly believe a technical book should be judged

not only by who wrote it, but also by who reviewed it.

At Oracle, I work with the best and brightest people I have ever known, and they all have

contributed in one way or another. I would like to thank Ken Jacobs in particular for his sup-

port and enthusiasm.

I would also like to thank everyone I work with for their support during this book-writing

ordeal. It took a lot more time and energy than I ever imagined, and I appreciate everyone’s

flexibility in that regard. In particular, I would like to thank Tim Hoechst and Mike Hichwa,

whom I’ve worked with and known for over 12 years now. Their constant questioning and

pushing helped me to discover things that I would never have even thought of investigating

on my own.

I would also like to acknowledge the people who use the Oracle software and ask so many

good questions. Without them, I would never even have thought of writing this book. Much of

what is included here is a direct result of someone asking me “how” or “why” at one time or

another.

Lastly, but most important, I would like to acknowledge the unceasing support I’ve

received from my family. You know you must be important to someone when you try to do

something that takes a lot of “outside of work hours” and someone lets you know about it.

Without the continual support of my wife Lori, son Alan, and daughter Megan, I don’t see

how I could have finished this book.

xvi

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xvii

Introduction

The inspiration for the material contained in this book comes from my experiences develop-

ing Oracle software, and from working with fellow Oracle developers and helping them build

reliable and robust applications based on the Oracle database. The book is basically a reflec-

tion of what I do every day and of the issues I see people encountering each and every day.

I covered what I felt was most relevant, namely the Oracle database and its architecture.

I could have written a similarly titled book explaining how to develop an application using a

specific language and architecture—for example, one using JavaServer Pages that speaks to

Enterprise JavaBeans, which in turn uses JDBC to communicate with Oracle. However, at the

end of the day, you really do need to understand the topics covered in this book in order to

build such an application successfully. This book deals with what I believe needs to be univer-

sally known to develop successfully with Oracle, whether you are a Visual Basic programmer

using ODBC, a Java programmer using EJBs and JDBC, or a Perl programmer using DBI Perl.

This book does not promote any specific application architecture; it does not compare three-

tier to client/server. Rather, it covers what the database can do and what you must understand

about the way it works. Since the database is at the heart of any application architecture, the

book should have a broad audience.

In writing this book, I completely revised an updated the architecture sections from

Expert One-on-One Oracle and added substantial new material. There have been three data-

base releases since Oracle 8.1.7, the release upon which the original book was based: two

Oracle9i releases and Oracle Database 10g Release 1, which is the current production release

of Oracle at the time of this writing. As such, there was a lot of new functionality and many

new features to cover.

The sheer volume of new material required in updating Expert One-on-One Oracle for 9i

and 10g was at the heart of the decision to split it into two books—an already large book was

getting unmanageable. The second book will be called Expert Oracle Programming.

As the title suggests, Expert Oracle Database Architecture concentrates on the database

architecture and how the database itself works. I cover the Oracle database architecture in

depth—the files, memory structures, and processes that comprise an Oracle database and

instance. I then move on to discuss important database topics such as locking, concurrency

controls, how transactions work, and redo and undo, and why it is important for you to know

about these things. Lastly, I examine the physical structures in the database such as tables,

indexes, and datatypes, covering techniques for making optimal use of them.

What This Book Is About

One of the problems with having plenty of development options is that it’s sometimes hard to

figure out which one might be the best choice for your particular needs. Everyone wants as

much flexibility as possible (as many choices as they can possibly have), but they also want

things to be very cut and dried—in other words, easy. Oracle presents developers with almost

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unlimited choice. No one ever says, “You can’t do that in Oracle”; rather, they say, “How many

different ways would you like to do that in Oracle?” I hope that this book will help you make

the correct choice.

This book is aimed at those people who appreciate the choice but would also like some

guidelines and practical implementation details on Oracle features and functions. For example,

Oracle has a really neat feature called parallel execution. The Oracle documentation tells you

how to use this feature and what it does. Oracle documentation does not, however, tell you

when you should use this feature and, perhaps even more important, when you should not use

this feature. It doesn’t always tell you the implementation details of this feature, and if you’re

not aware of them, this can come back to haunt you (I’m not referring to bugs, but the way the

feature is supposed to work and what it was really designed to do).

In this book I strove to not only describe how things work, but also explain when and

why you would consider using a particular feature or implementation. I feel it is important to

understand not only the “how” behind things, but also the “when” and “why”—as well as the

“when not” and “why not”!

Who Should Read This Book

The target audience for this book is anyone who develops applications with Oracle as the

database back end. It is a book for professional Oracle developers who need to know how to

get things done in the database. The practical nature of the book means that many sections

should also be very interesting to the DBA. Most of the examples in the book use SQL*Plus to

demonstrate the key features, so you won’t find out how to develop a really cool GUI—but you

will find out how the Oracle database works, what its key features can do, and when they

should (and should not) be used.

This book is for anyone who wants to get more out of Oracle with less work. It is for any-

one who wants to see new ways to use existing features. It is for anyone who wants to see how

these features can be applied in the real world (not just examples of how to use the feature,

but why the feature is relevant in the first place). Another category of people who would find

this book of interest is technical managers in charge of the developers who work on Oracle

projects. In some respects, it is just as important that they understand why knowing the data-

base is crucial to success. This book can provide ammunition for managers who would like to

get their personnel trained in the correct technologies or ensure that personnel already know

what they need to know.

To get the most out of this book, the reader should have

• Knowledge of SQL. You don’t have to be the best SQL coder ever, but a good working

knowledge will help.

• An understanding of PL/SQL. This isn’t a prerequisite, but it will help you to “absorb”

the examples. This book will not, for example, teach you how to program a FOR loop or

declare a record type—the Oracle documentation and numerous books cover this well.

However, that’s not to say that you won’t learn a lot about PL/SQL by reading this book.

You will. You’ll become very intimate with many features of PL/SQL and you’ll see new

ways to do things, and you’ll become aware of packages/features that perhaps you

didn’t know existed.

■INTRODUCTIONxviii

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• Exposure to some third-generation language (3GL), such as C or Java. I believe that any-

one who can read and write code in a 3GL language will be able to successfully read and

understand the examples in this book.

• Familiarity with the Oracle Concepts manual.

A few words on that last point: due to the Oracle documentation set’s vast size, many

people find it to be somewhat intimidating. If you’re just starting out or haven’t read any of

it as yet, I can tell you that the Oracle Concepts manual is exactly the right place to start. It’s

about 700 pages long and touches on many of the major Oracle concepts that you need to

know about. It may not give you each and every technical detail (that’s what the other 10,000

to 20,000 pages of documentation are for), but it will educate you on all the important con-

cepts. This manual touches the following topics (to name a few):

• The structures in the database, and how data is organized and stored

• Distributed processing

• Oracle’s memory architecture

• Oracle’s process architecture

• Schema objects you will be using (tables, indexes, clusters, and so on)

• Built-in datatypes and user-defined datatypes

• SQL stored procedures

• How transactions work

• The optimizer

• Data integrity

• Concurrency control

I will come back to these topics myself time and time again. These are the fundamentals—

without knowledge of them, you will create Oracle applications that are prone to failure. I

encourage you to read through the manual and get an understanding of some of these topics.

How This Book Is Structured

To help you use this book, most chapters are organized into four general sections (described

in the list that follows). These aren’t rigid divisions, but they will help you navigate quickly to

the area you need more information on. This book has 15 chapters, and each is like a “mini-

book”—a virtually stand-alone component. Occasionally, I refer to examples or features in

other chapters, but you could pretty much pick a chapter out of the book and read it on its

own. For example, you don’t have to read Chapter 10 on database tables to understand or

make use of Chapter 14 on parallelism.

■INTRODUCTION xix

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