Any organization that uses the Oracle relational database management system (RDBMS) these days needs to use multiple databases. There are many reasons to use more than a single database in a distributed database system:
Different databases may be associated with particular business functions, such as manufacturing or human resources.
Databases may be aligned with geographical boundaries, such as a behemoth database at a headquarters site and smaller databases at regional offices.
Two different databases may be required to access the same data in different ways, such as an order entry database whose transactions are aggregated and analyzed in a data warehouse.
A busy Internet commerce site may create multiple copies of the same database to attain horizontal scalability.
A copy of a production database may be created to serve as a development test bed.
In a distributed database environment, data in two or more databases is accessible as if it were in a single database. Usually, the different databases are on different servers, which may be located at the same site or a continent away. Communication between the servers takes place via SQL*Net (for Oracle7) or Net8 (for Oracle8).
Distributed database environments offer a number of benefits over single- database systems, including:
This book describes how you can use multiple databases and the distributed features of Oracle to best advantage. It covers:
Charles Dye is the database architect for Excite, Inc. (www.excite.com), where he is responsible for the design and implementation of the databases theat supply content to some of the world's busiest Web sites. Prior to joining Excite, he was the senior database administrator for The Dialog Corporation. Charles also operates a small but growing consultancy with clients in the San Francisco Bay area and Hong Kong. Once upon a time, before fleeing the East Coast for California skies, Charles taught math and physics at the Georgetown Day School in Washington DC. Charles is a frequent speaker at regional and national Oracle events such as Oracle Open World and IOUG-A Live. His favorite topics are distributed databases in general and advanced replication in particular. He also writes for the Northern California Oracle Users Group newsletter and is an active contributor to the Oracle Internet list server. Look for Charles' upcoming O'Reilly book, Oracle Distributed Systems, available later in 1998. Charles lives in Los Altos, California, with his wife Kathy, daughter Natalie, and labrador Jed. You can email him at firstname.lastname@example.org.
Our look is the result of reader comments, our own experimentation, and feedback from distribution channels. Distinctive covers complement our distinctive approach to technical topics, breathing personality and life into potentially dry subjects. Butterflies are featured on the cover of Oracle Distributed Systems. These are three of the thousands of species of butterfly. Butterflies, along with moths and skippers, make up the order Lepidoptera. The word "Lepidoptera" is derived from the Greek words lepic, meaning "scale," and pteron, meaning "wing." And, in fact, butterfly and moth wings are covered entirely in tiny, overlapping scales. The coloration of these fragile scales is what creates the spectacular, shimmering colors of the butterfly. The wing membrane itself is transparent and without color. Butterfly scales and hairs are covered in a thin layer of wax, making these insects water-repellent. Most butterflies fly by fluttering their wings at a relatively slow rate, sometimes as slowly as 10 beats per second, approximately four miles per hour. Unlike many other insects, who beat their wings so fast that they become just a blur in flight, the butterfly's wings are clearly visible during its fluttering flight. Butterflies are as well known for their four-stage metamorphosis as they are for their colorful wings and graceful fluttering. An adult female butterfly lays a large number of eggs, usually on or near food plants. The larva, better known as the caterpillar, develops within the egg and eats its way out. It then continues to eat almost constantly for a period ranging from one month to two years, depending on the butterfly species, periodically molting its skin during the process. The caterpillar then produces a pupa, or chrysalis, a mummylike structure. When the adult butterfly is fully formed, it breaks out of the pupa, its body and wings harden, and it takes off in search of food. Melanie Wang was the production editor, and Norma Emory was the copy editor for Oracle Distributed Systems. Sheryl Avruch was the production manager, and Jane Ellin and Ellie Maden provided quality control reviews. Betty Hugh and Sebastian Banker provided production support. Chris Reilley created the illustrations using Adobe Photoshop 5 and Macromedia FreeHand 8. Mike Sierra provided FrameMaker technical support. Ruth Rautenberg wrote the index. Edie Freedman designed the cover of this book, using a 19th-century engraving from the Dover Pictorial Archive. The cover layout was produced by Kathleen Wilson with QuarkXPress 3.32 using the ITC Garamond font. Kathleen Wilson designed the diskette label. The inside layout was designed by Nancy Priest and Alicia Cech and implemented in FrameMaker 5.5 by Mike Sierra. The text and heading fonts are ITC Garamond Light and Garamond Book. This colophon was written by Clairemarie Fisher O'Leary. Whenever possible, our books use a durable and flexible lay-flat binding, either RepKover or Otabind. If the page count exceeds the mamximum bulk possible for this type of binding, perfect binding is used.