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32            <h2 class="title"><a id="introduction"></a>Chapter��1.��Introduction to Berkeley DB </h2>
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37      <div class="toc">
38        <p>
39          <b>Table of Contents</b>
40        </p>
41        <dl>
42          <dt>
43            <span class="sect1">
44              <a href="introduction.html#aboutthismanual">About This Manual</a>
45            </span>
46          </dt>
47          <dt>
48            <span class="sect1">
49              <a href="concepts.html">Berkeley DB Concepts</a>
50            </span>
51          </dt>
52          <dt>
53            <span class="sect1">
54              <a href="accessmethods.html">Access Methods</a>
55            </span>
56          </dt>
57          <dd>
58            <dl>
59              <dt>
60                <span class="sect2">
61                  <a href="accessmethods.html#selectAM">Selecting Access Methods</a>
62                </span>
63              </dt>
64              <dt>
65                <span class="sect2">
66                  <a href="accessmethods.html#BTreeVSHash">Choosing between BTree and Hash</a>
67                </span>
68              </dt>
69              <dt>
70                <span class="sect2">
71                  <a href="accessmethods.html#QueueVSRecno">Choosing between Queue and Recno</a>
72                </span>
73              </dt>
74            </dl>
75          </dd>
76          <dt>
77            <span class="sect1">
78              <a href="databaseLimits.html">Database Limits and Portability</a>
79            </span>
80          </dt>
81          <dt>
82            <span class="sect1">
83              <a href="environments.html">Environments</a>
84            </span>
85          </dt>
86          <dt>
87            <span class="sect1">
88              <a href="coreExceptions.html">Exception Handling</a>
89            </span>
90          </dt>
91          <dt>
92            <span class="sect1">
93              <a href="returns.html">Error Returns</a>
94            </span>
95          </dt>
96          <dt>
97            <span class="sect1">
98              <a href="gettingit.html">Getting and Using DB </a>
99            </span>
100          </dt>
101        </dl>
102      </div>
103      <p>
104    Welcome to Berkeley DB (DB).  DB is a general-purpose embedded
105    database engine that is capable of providing a wealth of data management services.
106    It is designed from the ground up for high-throughput applications requiring
107    in-process, bullet-proof management of mission-critical data. DB can
108    gracefully scale from managing a few bytes to terabytes of data. For the most
109    part, DB is limited only by your system's available physical resources.
110  </p>
111      <p>
112         You use DB through a series of Java APIs which give you the
113          ability to read and write your data, manage your database(s), and
114          perform other more advanced activities such as managing
115          transactions. 
116            
117  </p>
118      <p>
119    Because DB is an embedded database engine, it is extremely fast. You compile
120    and link it into your application in the same way as you would any
121    third-party library. This means that DB runs in the same process space
122    as does your application, allowing you to avoid the high cost of
123    interprocess communications incurred by stand-alone database servers.
124  </p>
125      <p>
126    To further improve performance, DB offers an in-memory cache designed to
127    provide rapid access to your most frequently used data. Once configured,
128    cache usage is transparent. It requires very little attention on the part
129    of the application developer.
130  </p>
131      <p>
132    Beyond raw speed, DB is also extremely configurable. It provides several
133    different ways of organizing your data in its databases. Known as
134    <span class="emphasis"><em>access methods</em></span>, each such data organization mechanism
135    provides different characteristics that are appropriate for different data
136    management profiles. (Note that this manual focuses almost entirely on the
137    BTree access method as this is the access method used by the vast majority
138    of DB applications).
139  </p>
140      <p>
141    To further improve its configurability, DB offers many different
142    subsystems, each of which can be used to extend DB's capabilities. For
143    example, many applications require write-protection of their data so
144    as to ensure that data is never left in an inconsistent state for any
145    reason (such as software bugs or hardware failures). For those
146    applications, a transaction subsystem can be enabled and used to
147    transactional-protect database writes.
148  </p>
149      <p>
150    The list of operating systems on which DB is available is too long to
151    detail here. Suffice to say that it is available on all major commercial
152    operating systems, as well as on many embedded platforms.
153  </p>
154      <p>
155    Finally, DB is available in a wealth of programming languages.
156    DB is officially supported in C, C++, and Java, but the library is also
157    available in many other languages, especially scripting languages such as
158    Perl and Python. 
159  </p>
160      <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
161        <h3 class="title">Note</h3>
162        <p>
163        Before going any further, it is important to mention that DB is not
164        a relational database (although you could use it to build a relational 
165        database). Out of the box, DB does not provide higher-level features
166        such as triggers, or a high-level query language such as SQL. 
167        Instead, DB provides just those minimal
168        APIs required to store and retrieve your data as
169        efficiently as possible.
170   </p>
171      </div>
172      <div class="sect1" lang="en" xml:lang="en">
173        <div class="titlepage">
174          <div>
175            <div>
176              <h2 class="title" style="clear: both"><a id="aboutthismanual"></a>About This Manual</h2>
177            </div>
178          </div>
179          <div></div>
180        </div>
181        <p>
182        This manual introduces DB. As such, this book does not examine
183        intermediate or advanced features such as threaded library usage or
184        transactional usage. Instead, this manual provides a step-by-step
185        introduction to DB's basic concepts and library usage. 
186    </p>
187        <p>
188        Specifically, this manual introduces DB environments, databases,
189        database records, and storage and retrieval of database records. This
190        book also introduces cursors and their usage, and it describes
191        secondary databases. 
192    </p>
193        <p>
194        For the most part, this manual focuses on the BTree access method. A
195        chapter is given at the end of this manual that describes some of the
196        concepts involving BTree usage, such as duplicate record management and comparison
197        routines.
198    </p>
199        <p>
200        Examples are given throughout this book that are designed to illustrate
201        API usage.  At the end of each 
202        <span>chapter,</span> 
203         
204        a complete example is given that
205        is designed to reinforce the concepts covered in that 
206        <span>chapter.</span> 
207         
208        In addition to being presented in this book, these final programs are also 
209        available in the DB software distribution. You can find them in
210     </p>
211        <pre class="programlisting"><span class="emphasis"><em>DB_INSTALL</em></span>/examples_cxx/getting_started</pre>
212        <p>
213         where <tt class="literal"><span class="emphasis"><em>DB_INSTALL</em></span></tt> is the
214         location where you placed your DB distribution.
215     </p>
216        <p> 
217        This book uses the C++ programming languages for its examples.
218        Note that versions of this book exist for the C and Java languages as
219        well.  
220    </p>
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