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<h2 class="title" style="clear: both"><a id="mutexset_align"></a>DbEnv::mutex_set_align()</h2>
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<pre class="programlisting">#include <db_cxx.h>
int
DbEnv::mutex_set_align(u_int32_t align); </pre>
<p>
Set the mutex alignment, in bytes.
</p>
<p>
It is sometimes advantageous to align mutexes on specific byte
boundaries in order to minimize cache line collisions. The
<code class="methodname">DbEnv::mutex_set_align()</code> method specifies an alignment for mutexes
allocated by Berkeley DB.
</p>
<p>
The database environment's mutex alignment may also be configured
using the environment's <a href="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class="olink">DB_CONFIG</a> file. The
syntax of the entry in that file is a single line with the string
"mutex_set_align", one or more whitespace characters, and the mutex
alignment in bytes. Because the <a href="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class="olink">DB_CONFIG</a> file is
read when the database environment is opened, it will silently
overrule configuration done before that time.
</p>
<p>
The <code class="methodname">DbEnv::mutex_set_align()</code> method configures a database
environment, not only operations performed using the specified
<a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a> handle.
</p>
<p>
The <code class="methodname">DbEnv::mutex_set_align()</code> method may not be called after the
<a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a> method is
called. If the database environment already exists when
<a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a> is called, the
information specified to <code class="methodname">DbEnv::mutex_set_align()</code> will be ignored.
</p>
<p>
The <code class="methodname">DbEnv::mutex_set_align()</code> <span>
<span>
method either returns a non-zero error value or throws an
exception that encapsulates a non-zero error value on
failure, and returns 0 on success.
</span>
</span>
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<h3 class="title"><a id="id1698905"></a>Parameters</h3>
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<h4 class="title"><a id="id1699240"></a>align</h4>
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<p>
The <span class="bold"><strong>align</strong></span> parameter is the mutex
alignment, in bytes. The mutex alignment must be a power-of-two.
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<h3 class="title"><a id="id1699397"></a>Errors</h3>
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<p>
The <code class="methodname">DbEnv::mutex_set_align()</code> <span>
<span>
method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a>
exception, encapsulating one of the following non-zero errors, or return one
of the following non-zero errors:
</span>
</span>
</p>
<div class="sect3" lang="en" xml:lang="en">
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<h4 class="title"><a id="id1699160"></a>EINVAL</h4>
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<p>
If the method was called after <a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a>
was called; or if an invalid flag value or parameter was specified.
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<h3 class="title"><a id="id1699161"></a>Class</h3>
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<a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a>
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<h3 class="title"><a id="id1699229"></a>See Also</h3>
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<a class="xref" href="mutex.html#mutexlist" title="Mutex Methods">Mutex Methods</a>
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