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<title>Berkeley DB: DB_ENV->set_shm_key</title>
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<h1>DB_ENV->set_shm_key</h1>
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<a href="../api_c/c_index.html"><img src="../images/api.gif" alt="API"></a><a href="../reftoc.html"><img src="../images/ref.gif" alt="Ref"></a>
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DB_ENV->set_shm_key(DB_ENV *dbenv, long shm_key);
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<p>Specify a base segment ID for Berkeley DB environment shared memory regions
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created in system memory on VxWorks or systems supporting X/Open-style
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shared memory interfaces; for example, UNIX systems supporting
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<b>shmget</b>(2) and related System V IPC interfaces.
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<p>This base segment ID will be used when Berkeley DB shared memory regions are
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first created. It will be incremented a small integer value each time
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a new shared memory region is created; that is, if the base ID is 35,
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the first shared memory region created will have a segment ID of 35,
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and the next one will have a segment ID between 36 and 40 or so. A
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Berkeley DB environment always creates a master shared memory region; an
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additional shared memory region for each of the subsystems supported by
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the environment (Locking, Logging, Memory Pool and Transaction); plus
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an additional shared memory region for each additional memory pool cache
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that is supported. Already existing regions with the same segment IDs
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will be removed. See <a href="../ref/env/region.html">Shared Memory
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Regions</a> for more information.
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<p>The intent behind this interface is two-fold: without it, applications
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have no way to ensure that two Berkeley DB applications don't attempt to use
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the same segment IDs when creating different Berkeley DB environments. In
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addition, by using the same segment IDs each time the environment is
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created, previously created segments will be removed, and the set of
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segments on the system will not grow without bound.
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<p>The DB_ENV->set_shm_key interface may be used only to configure Berkeley DB before
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the <a href="../api_c/env_open.html">DB_ENV->open</a> interface is called.
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<p>The DB_ENV->set_shm_key function returns a non-zero error value on failure and 0 on success.
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<p>The database environment's base segment ID may also be set using the environment's
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<b>DB_CONFIG</b> file. The syntax of the entry in that file is a
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single line with the string "set_shm_key", one or more whitespace characters,
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and the ID. Because the <b>DB_CONFIG</b> file is read when the database
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environment is opened, it will silently overrule configuration done
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<p>The DB_ENV->set_shm_key function may fail and return a non-zero error for the following conditions:
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<p><dt>EINVAL<dd>An invalid flag value or parameter was specified.
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<p>Called after <a href="../api_c/env_open.html">DB_ENV->open</a> was called.
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<p>The DB_ENV->set_shm_key function may fail and return a non-zero error for errors specified for other Berkeley DB and C library or system functions.
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If a catastrophic error has occurred, the DB_ENV->set_shm_key function may fail and return
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<a href="../ref/program/errorret.html#DB_RUNRECOVERY">DB_RUNRECOVERY</a>, in which case all subsequent Berkeley DB calls will fail
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<a href="../api_c/env_create.html">db_env_create</a>,
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<a href="../api_c/env_close.html">DB_ENV->close</a>,
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<a href="../api_c/env_err.html">DB_ENV->err</a>, <a href="../api_c/env_err.html">DB_ENV->errx</a>
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<a href="../api_c/env_open.html">DB_ENV->open</a>,
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<a href="../api_c/env_remove.html">DB_ENV->remove</a>,
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<a href="../api_c/env_set_alloc.html">DB_ENV->set_alloc</a>,
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<a href="../api_c/env_set_cachesize.html">DB_ENV->set_cachesize</a>,
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<a href="../api_c/env_set_data_dir.html">DB_ENV->set_data_dir</a>,
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<a href="../api_c/env_set_errcall.html">DB_ENV->set_errcall</a>,
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<a href="../api_c/env_set_errfile.html">DB_ENV->set_errfile</a>,
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<a href="../api_c/env_set_errpfx.html">DB_ENV->set_errpfx</a>,
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<a href="../api_c/env_set_feedback.html">DB_ENV->set_feedback</a>,
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<a href="../api_c/env_set_flags.html">DB_ENV->set_flags</a>,
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<a href="../api_c/env_set_mutexlocks.html">DB_ENV->set_mutexlocks</a>,
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<a href="../api_c/env_set_pageyield.html">db_env_set_pageyield</a>,
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<a href="../api_c/env_set_paniccall.html">DB_ENV->set_paniccall</a>,
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<a href="../api_c/env_set_panicstate.html">db_env_set_panicstate</a>,
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<a href="../api_c/env_set_rec_init.html">DB_ENV->set_recovery_init</a>,
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<a href="../api_c/env_set_rpc_server.html">DB_ENV->set_rpc_server</a>,
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<a href="../api_c/env_set_region_init.html">db_env_set_region_init</a>,
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<a href="../api_c/env_set_shm_key.html">DB_ENV->set_shm_key</a>,
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<a href="../api_c/env_set_tas_spins.html">db_env_set_tas_spins</a>,
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<a href="../api_c/env_set_tmp_dir.html">DB_ENV->set_tmp_dir</a>,
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<a href="../api_c/env_set_verbose.html">DB_ENV->set_verbose</a>,
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<a href="../api_c/env_strerror.html">db_strerror</a>
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<a href="../api_c/env_version.html">db_version</a>.
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