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<!--$Id: env_set_shm_key.so,v 10.5 2000/08/09 15:45:52 sue Exp $-->
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<title>Berkeley DB: DBENV->set_shm_key</title>
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<h1>DBENV->set_shm_key</h1>
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<h3><pre>
#include <db.h>
<p>
int
DBENV->set_shm_key(DB_ENV *dbenv, long shm_key);
</pre></h3>
<h1>Description</h1>
<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, e.g., UNIX systems supporting
<b>shmget</b>(2) and related System V IPC interfaces.
<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 a segment ID between 36 and 40 or so. A Berkeley DB environment
always creates a master shared memory region, plus 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="../ref/env/region.html">Shared Memory Regions</a>
for more information.
<p>The intent behind this interface 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>The DBENV->set_shm_key interface may only be used to configure Berkeley DB before
the <a href="../api_c/env_open.html">DBENV->open</a> interface is called.
<p>The DBENV->set_shm_key function returns a non-zero error value on failure and 0 on success.
<p>The database environment's base segment ID may also be set using the environment's
<b>DB_CONFIG</b> 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 <b>DB_CONFIG</b> file is read when the database
environment is opened, it will silently overrule configuration done
before that time.
<h1>Errors</h1>
<p><dl compact>
<p><dt>EINVAL<dd>An invalid flag value or parameter was specified.
<p>Called after <a href="../api_c/env_open.html">DBENV->open</a> was called.
</dl>
<h1>See Also</h1>
<a href="../api_c/env_close.html">DBENV->close</a>,
<a href="../api_c/env_create.html">db_env_create</a>,
<a href="../api_c/env_open.html">DBENV->open</a>,
<a href="../api_c/env_remove.html">DBENV->remove</a>,
<a href="../api_c/db_err.html">DBENV->err</a>,
<a href="../api_c/env_strerror.html">db_strerror</a>,
<a href="../api_c/env_version.html">db_version</a>,
<a href="../api_c/env_set_cachesize.html">DBENV->set_cachesize</a>,
<a href="../api_c/env_set_errcall.html">DBENV->set_errcall</a>,
<a href="../api_c/env_set_errfile.html">DBENV->set_errfile</a>,
<a href="../api_c/env_set_errpfx.html">DBENV->set_errpfx</a>,
<a href="../api_c/env_set_flags.html">DBENV->set_flags</a>,
<a href="../api_c/env_set_mutexlocks.html">DBENV->set_mutexlocks</a>,
<a href="../api_c/env_set_paniccall.html">DBENV->set_paniccall</a>,
and
<a href="../api_c/env_set_verbose.html">DBENV->set_verbose</a>.
</tt>
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