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<title>Berkeley DB Reference Guide: Introduction</title>
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<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Environment</dl></h3></td>
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<h1 align=center>Introduction</h1>
<p>A Berkeley DB environment is an encapsulation of one or more databases, log
files and shared information about the database environment such as shared
memory buffer cache pages.
<p>The simplest way to administer a Berkeley DB application environment is to
create a single <b>home</b> 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>An environment may be shared by any number of applications as well as by
any number of threads within the applications. 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>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 <b>must</b> share an environment if consistency is
to be maintained between them.
<p>The Berkeley DB environment is created and described by the <a href="../../api_c/env_create.html">db_env_create</a>
and <a href="../../api_c/env_open.html">DBENV->open</a> interfaces. In situations where customization is
desired, such as storing log files on a separate disk drive, applications
must describe the customization by either creating an environment
configuration file in the environment home directory or by arguments
passed to the <a href="../../api_c/env_open.html">DBENV->open</a> interface. See the documentation on that
function for details on this procedure.
<p>Once an environment has been created, database files specified using
relative pathnames will be named relative to the home directory. Using
pathnames relative to the home directory allows the entire environment
to be easily moved to facilitate restoring and recovering a database in
a different directory or on a different system.
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