lemo的专栏

In the Terminator movies, an artificial intelligence called Skynet wages war on humans, chugging along for decades creating robots and killing off humanity. This is the dream of most ops people—not to destroy humanity, but to build a distributed system that will work long-term without relying on people carrying pagers. Skynet is still a pipe dream, unfortunately, because distributed systems are very difficult, both to design well and to keep running. A single database server has a couple of basic states: it’s either up or down. If you add another machine and divide your data between the two, you now have some sort of dependency between the servers. How does it affect one machine if the other goes down? Can your application handle either (or both) machines going down? What if the two machines are up, but can’t communicate? What if they can communicate, but only very, very, slowly? As you add more nodes, these problems just become more numerous and complex: what happens if entire parts of your cluster can’t communicate with other parts? What happens if one subset of machines crashes? What happens if you lose an entire data center? Suddenly, even taking a backup becomes difficult: how do you take a consistent snapshot of many terabytes of data across dozens of machines without freezing out the application trying to use the data? If you can get away with a single server, it is much simpler. However, if you want to store a large volume of data or access it at a rate higher than a single server can handle, you’ll need to set up a cluster. On the plus side, MongoDB tries to take care of a lot of the issues listed above. Keep in mind that this isn’t as simple as setting up a single mongod (then again, what is?). This book shows you how to set up a robust cluster and what to expect every step of the way.

The information that I gathered together in this book is the result of working with some of the most talented UNIX professionals on the topic. I have enjoyed every minute of my association with these UNIX gurus and it has been my pleasure to have the opportunity to gain so much knowledge from the pros. I want to thank every one of these experts for asking and answering questions over the last fifteen years. If my brother, Jim, had not kept telling me, “you should write a book,” after querying me for UNIX details on almost a weekly basis, I doubt this book would have ever been writ- ten. So, thanks Jim! I especially want to thank Jack Renfro at Daimler/Chrysler Corporation for giving me my first shell scripting project so long ago. I had to start with the man pages, but that is how I learned to dig deep to get an answer. Since then I have been on a mission to automate, through shell scripting, everything on every system that I come in contact with. I certainly value the years that I was able to work with Jack. I must also thank the talented people at Wiley Publishing. Margaret Eldridge started me on this project by letting me do my own thing, and Carol Long kept me going. Scott Amerman kept me on schedule, and Angela Smith did the edits that make my writing flow with ease. It has been a valuable experience for me to work with such a fine group of professionals at Wiley. I also want to thank Carole McClendon at Waterside Produc- tions for all of the support on this project. Carole is the best Agent that anyone could ever ask for. She is a true professional with the highest ethics. Of course my family had a lot to do with my success on this and every project. I want to thank Mom, Gene, Jim, Marcia, Rusty, Mallory, and Anica. I want to thank my Wife Robin for her understanding and support. The girls, Andrea and Ana, always keep a smile on my face, and Steve is always on my mind. I could not have written this book without the support of all of these people and the many others that remain unnamed. It has been an honor!

Many of the designations used by manufacturers and sellers to distinguish their prod- ucts are claimed as trademarks. Where those designations appear in this book, and The Pragmatic Programmers, LLC was aware of a trademark claim, the designations have been printed in initial capital letters or in all capitals. The Pragmatic Starter Kit, The Pragmatic Programmer, Pragmatic Programming, Pragmatic Bookshelf and the linking g device are trademarks of The Pragmatic Programmers, LLC. Every precaution was taken in the preparation of this book. However, the publisher assumes no responsibility for errors or omissions, or for damages that may result from the use of information (including program listings) contained herein. Our Pragmatic courses, workshops, and other products can help you and your team create better software and have more fun. For more information, as well as the latest Pragmatic titles, please visit us at

Introduction to Information Retrieval Introduction to Information Retrieval is the first textbook with a coherent treat- ment of classical and web information retrieval, including web search and the related areas of text classification and text clustering. Written from a computer science perspective, it gives an up-to-date treatment of all aspects of the design and implementation of systems for gathering, indexing, and searching documents and of methods for evaluating systems, along with an introduction to the use of machine learning methods on text collections. Designed as the primary text for a graduate or advanced undergraduate course in information retrieval, the book will also interest researchers and professionals. A complete set of lecture slides and exercises that accompany the book are available on the web. Christopher D. Manning is Associate Professor of Computer Science and Lin- guistics at Stanford University. Prabhakar Raghavan is Head of Yahoo! Research and a Consulting Professor of Computer Science at Stanford University. ̈ Hinrich Schutze is Chair of Theoretical Computational Linguistics at the In- stitute for Natural Language Processing, University of Stuttgart.

Your class library works, but could it be better? Refactoring: Improving the Design of Existing Code shows how refactoring can make object-oriented code simpler and easier to maintain. Today refactoring requires considerable design know-how, but once tools become available, all programmers should be able to improve their code using refactoring techniques. Besides an introduction to refactoring, this handbook provides a catalog of dozens of tips for improving code. The best thing about Refactoring is its remarkably clear presentation, along with excellent nuts-and-bolts advice, from object expert Martin Fowler. The author is also an authority on software patterns and UML, and this experience helps make this a better book, one that should be immediately accessible to any intermediate or advanced object-oriented developer. (Just like patterns, each refactoring tip is presented with a simple name, a "motivation," and examples using Java and UML.) Early chapters stress the importance of testing in successful refactoring. (When you improve code, you have to test to verify that it still works.) After the discussion on how to detect the "smell" of bad code, readers get to the heart of the book, its catalog of over 70 "refactorings"--tips for better and simpler class design. Each tip is illustrated with "before" and "after" code, along with an explanation. Later chapters provide a quick look at refactoring research. Like software patterns, refactoring may be an idea whose time has come. This groundbreaking title will surely help bring refactoring to the programming mainstream. With its clear advice on a hot new topic, Refactoring is sure to be essential reading for anyone who writes or maintains object-oriented software. --Richard Dragan Topics Covered: Refactoring, improving software code, redesign, design tips, patterns, unit testing, refactoring research, and tools. Book News, Inc. A guide to refactoring, the process of changing a software system so that it does not alter the external behavior of the code yet improves its internal structure, for professional programmers. Early chapters cover general principles, rationales, examples, and testing. The heart of the book is a catalog of refactorings, organized in chapters on composing methods, moving features between objects, organizing data, simplifying conditional expressions, and dealing with generalizations

Preface The computing world has undergone a revolution since the publication of The C Programming Language in 1978. Big computers are much bigger, and personal computers have capabilities that rival mainframes of a decade ago. During this time, C has changed too, although only modestly, and it has spread far beyond its origins as the language of the UNIX operating system. The growing popularity of C, the changes in the language over the years, and the creation of compilers by groups not involved in its design, combined to demonstrate a need for a more precise and more contemporary definition of the language than the first edition of this book provided. In 1983, the American National Standards Institute (ANSI) established a committee whose goal was to produce ``an unambiguous and machine-independent definition of the language C'', while still retaining its spirit. The result is the ANSI standard for C. The standard formalizes constructions that were hinted but not described in the first edition, particularly structure assignment and enumerations. It provides a new form of function declaration that permits cross-checking of definition with use. It specifies a standard library, with an extensive set of functions for performing input and output, memory management, string manipulation, and similar tasks. It makes precise the behavior of features that were not spelled out in the original definition, and at the same time states explicitly which aspects of the language remain machine-dependent. This Second Edition of The C Programming Language describes C as defined by the ANSI standard. Although we have noted the places where the language has evolved, we have chosen to write exclusively in the new form. For the most part, this makes no significant difference; the most visible change is the new form of function declaration and definition. Modern compilers already support most features of the standard. We have tried to retain the brevity of the first edition. C is not a big language, and it is not well served by a big book. We have improved the exposition of critical features, such as pointers, that are central to C programming. We have refined the original examples, and have added new examples in several chapters. For instance, the treatment of complicated declarations is augmented by programs that convert declarations into words and vice versa. As before, all examples have been tested directly from the text, which is in machine-readable form. Appendix A, the reference manual, is not the standard, but our attempt to convey the essentials of the standard in a smaller space. It is meant for easy comprehension by programmers, but not as a definition for compiler writers -- that role properly belongs to the standard itself. Appendix B is a summary of the facilities of the

Object-oriented programming is the current cure-all — although it has been around for much more then ten years. At the core, there is little more to it then finally applying the good programming principles which we have been taught for more then twenty years. C++ (Eiffel, Oberon-2, Smalltalk ... take your pick) is the New Language because it is object-oriented — although you need not use it that way if you do not want to (or know how to), and it turns out that you can do just as well with plain ANSI-C. Only object-orientation permits code reuse between pro- jects — although the idea of subroutines is as old as computers and good program- mers always carried their toolkits and libraries with them. This book is not going to praise object-oriented programming or condemn the Old Way. We are simply going to use ANSI-C to discover how object-oriented pro- gramming is done, what its techniques are, why they help us solve bigger prob- lems, and how we harness generality and program to catch mistakes earlier. Along the way we encounter all the jargon — classes, inheritance, instances, linkage, methods, objects, polymorphisms, and more — but we take it out of the realm of magic and see how it translates into the things we have known and done all along. I had fun discovering that ANSI-C is a full-scale object-oriented language. To share this fun you need to be reasonably fluent in ANSI-C to begin with — feeling comfortable with structures, pointers, prototypes, and function pointers is a must. Working through the book you will encounter all the newspeak — according to Orwell and Webster a language ‘‘designed to diminish the range of thought’’ — and I will try to demonstrate how it merely combines all the good programming princi- ples that you always wanted to employ into a coherent approach. As a result, you may well become a more proficient ANSI-C programmer. The first six chapters develop the foundations of object-oriented programming with ANSI-C. We start with a careful information hiding technique for abstract data types, add generic functions based on dynamic linkage and inherit code by judicious lengthening of structures. Finally, we put it all together in a class hierarchy that makes code much easier to maintain. Programming takes discipline. Good programming takes a lot of discipline, a large number of principles, and standard, defensive ways of doing things right. Pro- grammers use tools. Good programmers make tools to dispose of routine tasks once and for all. Object-oriented programming with ANSI-C requires a fair amount of immutable code — names may change but not the structures. Therefore, in chapter seven we build a small preprocessor to create the boilerplate required. It looks like yet another new object-oriented dialect language (yanoodl perhaps?) but it should not be viewed as such — it gets the dull parts out of the way and lets us concentrate on the creative aspects of problem solving with better techniques. ooc

Introduction C code. C code run. Run code run...please! —Barbara Ling All C programs do the same thing: look at a character and do nothing with it. —Peter Weinberger Have you ever noticed that there are plenty of C books with suggestive names like C Traps and Pitfalls, or The C Puzzle Book, or Obfuscated C and Other Mysteries, but other programming languages don't have books like that? There's a very good reason for this! C programming is a craft that takes years to perfect. A reasonably sharp person can learn the basics of C quite quickly. But it takes much longer to master the nuances of the language and to write enough programs, and enough different programs, to become an expert. In natural language terms, this is the difference between being able to order a cup of coffee in Paris, and (on the Metro) being able to tell a native Parisienne where to get off. This book is an advanced text on the ANSI C programming language. It is intended for people who are already writing C programs, and who want to quickly pick up some of the insights and techniques of experts. Expert programmers build up a tool kit of techniques over the years; a grab-bag of idioms, code fragments, and deft skills. These are acquired slowly over time, learned from looking over the shoulders of more experienced colleagues, either directly or while maintaining code written by others. Other lessons in C are self-taught. Almost every beginning C programmer independently rediscovers the mistake of writing:

Contents Preface Chapter 1 Meet Lucene Chapter 2 Indexing Chapter 3 Adding search to your application Chapter 4 Analysis Chapter 5 Advanced search techniques Chapter 6 Extending search Chapter 7 Parsing common document formats Chapter 8 Tools and extensions Chapter 9 Lucene ports Chapter 10 Administration and performance tuning Chapter 11 Case studies Appendix A Installing Lucene Appendix B Lucene index format Appendix C Resources Appendix D Using the benchmark (contrib) framework

Mining the Web Mining the Web Mining the Web Mining the Web

这是一本关于如果有效使用STL的书，感觉还可以。

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