Chapter 1. Introduction to Berkeley DB
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## Chapter 1. Introduction to Berkeley DB

Welcome to Berkeley DB (DB). DB is a general-purpose embedded database engine that is capable of providing a wealth of data management services. It is designed from the ground up for high-throughput applications requiring in-process, bullet-proof management of mission-critical data. DB can gracefully scale from managing a few bytes to terabytes of data. For the most part, DB is limited only by your system's available physical resources.

You use DB through a series of programming APIs which give you the ability to read and write your data, manage your database(s), and perform other more advanced activities such as managing transactions. The Java APIs that you use to interact with DB come in two basic flavors. The first is a high-level API that allows you to make Java classes persistent. The second is a lower-level API which provides additional flexibility when interacting with DB databases.

### Note

For long-time users of DB, the lower-level API is the traditional API that you are probably accustomed to using.

Because DB is an embedded database engine, it is extremely fast. You compile and link it into your application in the same way as you would any third-party library. This means that DB runs in the same process space as does your application, allowing you to avoid the high cost of interprocess communications incurred by stand-alone database servers.

To further improve performance, DB offers an in-memory cache designed to provide rapid access to your most frequently used data. Once configured, cache usage is transparent. It requires very little attention on the part of the application developer.

Beyond raw speed, DB is also extremely configurable. It provides several different ways of organizing your data in its databases. Known as access methods, each such data organization mechanism provides different characteristics that are appropriate for different data management profiles. (Note that this manual focuses almost entirely on the BTree access method as this is the access method used by the vast majority of DB applications).

To further improve its configurability, DB offers many different subsystems, each of which can be used to extend DB's capabilities. For example, many applications require write-protection of their data so as to ensure that data is never left in an inconsistent state for any reason (such as software bugs or hardware failures). For those applications, a transaction subsystem can be enabled and used to transactional-protect database writes.

The list of operating systems on which DB is available is too long to detail here. Suffice to say that it is available on all major commercial operating systems, as well as on many embedded platforms.

Finally, DB is available in a wealth of programming languages. DB is officially supported in C, C++, and Java, but the library is also available in many other languages, especially scripting languages such as Perl and Python.

### Note

Before going any further, it is important to mention that DB is not a relational database (although you could use it to build a relational database). Out of the box, DB does not provide higher-level features such as triggers, or a high-level query language such as SQL. Instead, DB provides just those minimal APIs required to store and retrieve your data as efficiently as possible.

## About This Manual

This manual introduces DB. As such, this book does not examine intermediate or advanced features such as threaded library usage or transactional usage. Instead, this manual provides a step-by-step introduction to DB's basic concepts and library usage.

Specifically, this manual introduces the high-level Java API (the DPL), as well as the "base" Java API that the DPL relies upon. Regardless of the API set that you choose to use, there are a series of concepts and APIs that are common across the product. This manual starts by providing a high-level examination of DB. It then describes the APIs you use regardless of the API set that you choose to use. It then provides information on using the Direct Persistence Layer (DPL) API, followed by information on using the more extensive "base" API.

Examples are given throughout this book that are designed to illustrate API usage. At the end of each chapter or section in this book, a complete example is given that is designed to reinforce the concepts covered in that chapter or section. In addition to being presented in this book, these final programs are also available in the DB software distribution. You can find them in

    DB_INSTALL/examples_java/db/GettingStarted

where `DB_INSTALL` is the location where you placed your DB distribution.

This book uses the Java programming languages for its examples. Note that versions of this book exist for the C and C++ languages as well.

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