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<p>Library Version 11.2.5.3</p>
</div>
<table width="100%" summary="Navigation header">
<tr>
<th colspan="3" align="center">File naming</th>
</tr>
<tr>
<td width="20%" align="left"><a accesskey="p" href="env_db_config.html">Prev</a> </td>
<th width="60%" align="center">Chapter 9.
The Berkeley DB Environment
</th>
<td width="20%" align="right"> <a accesskey="n" href="env_region.html">Next</a></td>
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</div>
<div class="sect1" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both"><a id="env_naming"></a>File naming</h2>
</div>
</div>
</div>
<div class="toc">
<dl>
<dt>
<span class="sect2">
<a href="env_naming.html#idp51749352">Specifying file naming to Berkeley DB</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="env_naming.html#idp51763728">Filename resolution in Berkeley DB</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="env_naming.html#idp51756464">Examples</a>
</span>
</dt>
</dl>
</div>
<p>
One of the most important tasks of the database environment is to
structure file naming within Berkeley DB. Cooperating applications (or
multiple invocations of the same application) must agree on the
location of the database environment, log files and other files used by
the Berkeley DB subsystems, and, of course, the database files.
Although it is possible to specify full pathnames to all Berkeley DB
methods, this is cumbersome and requires applications be recompiled
when database files are moved.
</p>
<p>
Applications are normally expected to specify a single directory home
for the database environment. This can be done easily in the call to
<a href="../api_reference/C/envopen.html" class="olink">DB_ENV->open()</a> by specifying a value for the
<span class="bold"><strong>db_home</strong></span> argument. There are more
complex configurations in which it may be desirable to override
<span class="bold"><strong>db_home</strong></span> or provide supplementary path
information.
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp51749352"></a>Specifying file naming to Berkeley DB</h3>
</div>
</div>
</div>
<p>
The following list describes the possible ways in which file naming
information may be specified to the Berkeley DB library. The
specific circumstances and order in which these ways are applied
are described in a subsequent paragraph.
</p>
<div class="variablelist">
<dl>
<dt>
<span class="term">db_home</span>
</dt>
<dd>
If the <span class="bold"><strong>db_home</strong></span> argument to
<a href="../api_reference/C/envopen.html" class="olink">DB_ENV->open()</a> is non-NULL, its value may be used as the
database home, and files named relative to its path.
</dd>
<dt>
<span class="term">DB_HOME</span>
</dt>
<dd>
<p>
If the DB_HOME environment variable is set when
<a href="../api_reference/C/envopen.html" class="olink">DB_ENV->open()</a> is called, its value may be used as the
database home, and files named relative to its
path.
</p>
<p>
The DB_HOME environment variable is intended to permit
users and system administrators to override application
and installation defaults. For example:
</p>
<pre class="programlisting">env DB_HOME=/database/my_home application</pre>
<p>
Application writers are encouraged to support the
<span class="bold"><strong>-h</strong></span> option found in the
supporting Berkeley DB utilities to let users specify a
database home.
</p>
</dd>
<dt>
<span class="term"><a href="../api_reference/C/env.html" class="olink">DB_ENV</a> methods</span>
</dt>
<dd>
<p>
There are four <a href="../api_reference/C/env.html" class="olink">DB_ENV</a> methods that affect file naming:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
The <a href="../api_reference/C/envadd_data_dir.html" class="olink">DB_ENV->add_data_dir()</a> method specifies a
directory to search for database files.
</p>
</li>
<li>
<p>
The <a href="../api_reference/C/envset_lg_dir.html" class="olink">DB_ENV->set_lg_dir()</a> method specifies a
directory in which to create logging files.
</p>
</li>
<li>
<p>
The <a href="../api_reference/C/envset_tmp_dir.html" class="olink">DB_ENV->set_tmp_dir()</a> method specifies a
directory in which to create backing temporary
files.
</p>
</li>
<li>
<p>
The <a href="../api_reference/C/envset_metadata_dir.html" class="olink">DB_ENV->set_metadata_dir()</a> method specifies the
directory in which to create persistent
metadata files used by the environment.
</p>
</li>
</ul>
</div>
<p>
These methods are intended to permit applications to
customize a file locations for an environment. For example,
an application writer can place data files and log
files in different directories or instantiate a new log
directory each time the application runs.
</p>
</dd>
<dt>
<span class="term">
<a class="link" href="env_db_config.html" title="DB_CONFIG configuration file">DB_CONFIG</a>
</span>
</dt>
<dd>
The same information specified to the <a href="../api_reference/C/env.html" class="olink">DB_ENV</a> methods may
also be specified using the
<a class="link" href="env_db_config.html" title="DB_CONFIG configuration file">DB_CONFIG</a>
configuration file.
</dd>
</dl>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp51763728"></a>Filename resolution in Berkeley DB</h3>
</div>
</div>
</div>
<p>
The following list describes the specific circumstances and order
in which the different ways of specifying file naming information
are applied. Berkeley DB filename processing proceeds sequentially
through the following steps:
</p>
<div class="variablelist">
<dl>
<dt>
<span class="term">absolute pathnames</span>
</dt>
<dd>
<p>
If the filename specified to a Berkeley DB function is
an <span class="emphasis"><em>absolute pathname</em></span>, that
filename is used without modification by Berkeley DB.
</p>
<p>
On UNIX systems, an absolute pathname is defined as any
pathname that begins with a leading slash
(<span class="bold"><strong>/</strong></span>).
</p>
<p>
On Windows systems, an absolute pathname is any
pathname that begins with a leading slash or leading
backslash (<span class="bold"><strong>\</strong></span>); or any
pathname beginning with a single alphabetic character,
a colon and a leading slash or backslash (for example,
<code class="filename">C:/tmp</code>).
</p>
</dd>
<dt>
<span class="term"><a href="../api_reference/C/env.html" class="olink">DB_ENV</a> methods, DB_CONFIG</span>
</dt>
<dd>
If a relevant configuration string (for example,
set_data_dir), is specified either by calling a <a href="../api_reference/C/env.html" class="olink">DB_ENV</a>
method or as a line in the
<a class="link" href="env_db_config.html" title="DB_CONFIG configuration file">DB_CONFIG</a> configuration
file, the value is prepended to the filename. If the
resulting filename is an absolute pathname, the filename is
used without further modification by Berkeley
DB.
</dd>
<dt>
<span class="term">db_home</span>
</dt>
<dd>
If the application specified a non-NULL
<span class="bold"><strong>db_home</strong></span> argument to
<a href="../api_reference/C/envopen.html" class="olink">DB_ENV->open()</a>, its value is prepended to the filename. If the
resulting filename is an absolute pathname, the filename is
used without further modification by Berkeley
DB.
</dd>
<dt>
<span class="term">DB_HOME</span>
</dt>
<dd>
If the <span class="bold"><strong>db_home</strong></span> argument is
NULL, the DB_HOME environment variable was set, and the
application has set the appropriate <a href="../api_reference/C/envopen.html#envopen_DB_USE_ENVIRON" class="olink">DB_USE_ENVIRON</a> or
<a href="../api_reference/C/envopen.html#envopen_DB_USE_ENVIRON_ROOT" class="olink">DB_USE_ENVIRON_ROOT</a> flags, its value is prepended to the
filename. If the resulting filename is an absolute
pathname, the filename is used without further modification
by Berkeley DB.
</dd>
<dt>
<span class="term">default</span>
</dt>
<dd>
Finally, all filenames are interpreted relative to the
current working directory of the process.
</dd>
</dl>
</div>
<p>
The common model for a Berkeley DB environment is one in which only
the DB_HOME environment variable, or the
<span class="bold"><strong>db_home</strong></span> argument is specified. In
this case, all data filenames are relative to that directory, and
all files created by the Berkeley DB subsystems will be created in
that directory.
</p>
<p>
The more complex model for a transaction environment might be one
in which a database home is specified, using either the DB_HOME
environment variable or the
<span class="bold"><strong>db_home</strong></span> argument to <a href="../api_reference/C/envopen.html" class="olink">DB_ENV->open()</a>; and
then the data directory and logging directory are set to the
relative pathnames of directories underneath the environment
home.
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp51756464"></a>Examples</h3>
</div>
</div>
</div>
<p>
Store all files in the directory <code class="filename">/a/database</code>:
</p>
<pre class="programlisting">dbenv->open(dbenv, "/a/database", flags, mode);</pre>
<p>
Create temporary backing files in
<code class="filename">/b/temporary</code>, and all other files in
<code class="filename">/a/database</code>:
</p>
<pre class="programlisting">dbenv->set_tmp_dir(dbenv, "/b/temporary");
dbenv->open(dbenv, "/a/database", flags, mode);</pre>
<p>
Store data files in <code class="filename">/a/database/datadir</code>, log
files in <code class="filename">/a/database/logdir</code>, and all other
files in the directory <code class="filename">/a/database</code>:
</p>
<pre class="programlisting">dbenv->set_lg_dir(dbenv, "logdir");
dbenv->set_data_dir(dbenv, "datadir");
dbenv->open(dbenv, "/a/database", flags, mode);</pre>
<p>
Store data files in <code class="filename">/a/database/data1</code> and
<code class="filename">/b/data2</code>, and all other files in the directory
<code class="filename">/a/database</code>. Any data files that are created
will be created in <code class="filename">/b/data2</code>, because it is the
first data file directory specified:
</p>
<pre class="programlisting">dbenv->set_data_dir(dbenv, "/b/data2");
dbenv->set_data_dir(dbenv, "data1");
dbenv->open(dbenv, "/a/database", flags, mode);</pre>
</div>
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