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<h2 class="title"><a id="env"></a>Chapter 9.
The Berkeley DB Environment
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<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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