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<th colspan="3" align="center">DbEnv::set_shm_key()</th>
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<h2 class="title" style="clear: both"><a id="envset_shm_key"></a>DbEnv::set_shm_key()</h2>
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<pre class="programlisting">#include <db_cxx.h>
int
DbEnv::set_shm_key(long shm_key); </pre>
<p>
Specify a base segment ID for Berkeley DB environment shared memory
regions created in system memory on VxWorks or systems supporting
X/Open-style shared memory interfaces; for example, UNIX systems
supporting <span class="bold"><strong>shmget</strong></span>(2) and related
System V IPC interfaces.
</p>
<p>
This base segment ID will be used when Berkeley DB shared memory
regions are first created. It will be incremented a small integer
value each time a new shared memory region is created; that is, if the
base ID is 35, the first shared memory region created will have a
segment ID of 35, and the next one will have a segment ID between 36
and 40 or so. A Berkeley DB environment always creates a master
shared memory region; an additional shared memory region for each of
the subsystems supported by the environment (Locking, Logging, Memory
Pool and Transaction); plus an additional shared memory region for
each additional memory pool cache that is supported. Already existing
regions with the same segment IDs will be removed. See
<a href="../../programmer_reference/env_region.html" class="olink">Shared Memory Regions</a>
for more information.
</p>
<p>
The intent behind this method is two-fold: without it, applications
have no way to ensure that two Berkeley DB applications don't attempt
to use the same segment IDs when creating different Berkeley DB
environments. In addition, by using the same segment IDs each time
the environment is created, previously created segments will be
removed, and the set of segments on the system will not grow without
bound.
</p>
<p>
The database environment's base segment ID 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 "set_shm_key", one
or more whitespace characters, and the ID. 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::set_shm_key()</code> method configures operations performed
using the specified <a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a> handle, not all
operations performed on the underlying database environment.
</p>
<p>
The <code class="methodname">DbEnv::set_shm_key()</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::set_shm_key()</code> must be consistent
with the existing environment or corruption can occur.
</p>
<p>
The <code class="methodname">DbEnv::set_shm_key()</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>
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp7586408"></a>Parameters</h3>
</div>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="idp7585760"></a>shm_key</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>shm_key</strong></span> parameter is the base
segment ID for the database environment.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp7569640"></a>Errors</h3>
</div>
</div>
</div>
<p>
The <code class="methodname">DbEnv::set_shm_key()</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">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="idp7600000"></a>EINVAL</h4>
</div>
</div>
</div>
<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.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp7601328"></a>Class</h3>
</div>
</div>
</div>
<p>
<a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a>
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp7588600"></a>See Also</h3>
</div>
</div>
</div>
<p>
<a class="xref" href="env.html#envlist" title="Database Environments and Related Methods">Database Environments and Related Methods</a>
</p>
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