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<h2 class="title"><a id="env"></a>Chapter 9. The Berkeley DB Environment </h2>
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<div class="toc">
<p>
<b>Table of Contents</b>
</p>
<dl>
<dt>
<span class="sect1">
<a href="env.html#env_intro">Database environment introduction</a>
</span>
</dt>
<dt>
<span class="sect1">
<a href="env_create.html">Creating a database
environment</a>
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<a href="env_size.html">Sizing a database environment</a>
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<span class="sect1">
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environment</a>
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<dt>
<span class="sect1">
<a href="env_db_config.html">DB_CONFIG configuration
file</a>
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<span class="sect1">
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<span class="sect2">
<a href="env_naming.html#idp1160456">Filename resolution in Berkeley DB</a>
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<a href="env_naming.html#idp1182752">Examples</a>
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<a href="env_remote.html">Remote filesystems</a>
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<h2 class="title" style="clear: both"><a id="env_intro"></a>Database environment introduction</h2>
</div>
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</div>
<p>
A Berkeley DB environment is an encapsulation of one or more
databases, log files and region files. Region files are the
shared memory areas that contain information about the
database environment such as memory pool cache pages. Only
databases are byte-order independent and only database files
can be moved between machines of different byte orders. Log
files can be moved between machines of the same byte order.
Region files are usually unique to a specific machine and
potentially to a specific operating system release.
</p>
<p>
The simplest way to administer a Berkeley DB application
environment is to create a single <span class="bold"><strong>home</strong></span>
directory that stores the files for the
applications that will share the environment. The environment
home directory must be created before any Berkeley DB
applications are run. Berkeley DB itself never creates the
environment home directory. The environment can then be
identified by the name of that directory.
</p>
<p>
An environment may be shared by any number of processes, as
well as by any number of threads within those processes. It is
possible for an environment to include resources from other
directories on the system, and applications often choose to
distribute resources to other directories or disks for
performance or other reasons. However, by default, the
databases, shared regions (the locking, logging, memory pool,
and transaction shared memory areas) and log files will be
stored in a single directory hierarchy.
</p>
<p>
It is important to realize that all applications sharing a
database environment implicitly trust each other. They have
access to each other's data as it resides in the shared
regions, and they will share resources such as buffer space
and locks. At the same time, any applications using the same
databases <span class="bold"><strong>must</strong></span> share an
environment if consistency is to be maintained between
them.
</p>
<p>
For more information on the operations supported by the
database environment handle, see the <a href="../api_reference/C/env.html#envlist" class="olink">Database Environments and Related
Methods</a> section in the
<em class="citetitle">Berkeley DB C API Reference Guide.</em>
</p>
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