110 lines
5.1 KiB
HTML
110 lines
5.1 KiB
HTML
<!--$Id: env_set_shm_key.html 63573 2008-05-23 21:43:21Z trent.nelson $-->
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<!--Copyright (c) 1997,2008 Oracle. All rights reserved.-->
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<html>
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<head>
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<title>Berkeley DB: DB_ENV->set_shm_key</title>
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<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
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<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++">
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</head>
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<body bgcolor=white>
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<table width="100%"><tr valign=top>
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<td>
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<b>DB_ENV->set_shm_key</b>
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</td>
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<td align=right>
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<a href="../api_c/api_core.html"><img src="../images/api.gif" alt="API"></a>
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<a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a></td>
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</tr></table>
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<hr size=1 noshade>
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<tt>
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<b><pre>
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#include <db.h>
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<p>
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int
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DB_ENV->set_shm_key(DB_ENV *dbenv, long shm_key);
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<p>
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int
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DB_ENV->get_shm_key(DB_ENV *dbenv, long *shm_keyp);
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</pre></b>
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<hr size=1 noshade>
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<b>Description: DB_ENV->set_shm_key</b>
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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.</p>
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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.</p>
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<p>The intent behind this method 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.</p>
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<p>The database environment's base segment ID may also be configured using the
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environment's <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> file. The syntax of the entry in that
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file is a single line with the string "set_shm_key", one or more whitespace
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characters, and the ID.
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Because the <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> file is read when the database environment
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is opened, it will silently overrule configuration done before that
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time.</p>
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<p>The DB_ENV->set_shm_key method configures operations performed using the specified
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<a href="../api_c/env_class.html">DB_ENV</a> handle, not all operations performed on the underlying
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database environment.</p>
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<p>The DB_ENV->set_shm_key method may not be called after the <a href="../api_c/env_open.html">DB_ENV->open</a> method is
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called.
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If the database environment already exists when
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<a href="../api_c/env_open.html">DB_ENV->open</a> is called, the information specified to DB_ENV->set_shm_key
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must be consistent with the existing environment or corruption can
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occur.</p>
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<p>The DB_ENV->set_shm_key method
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returns a non-zero error value on failure
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and 0 on success.
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</p>
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<b>Parameters</b> <br>
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<b>shm_key</b><ul compact><li>The <b>shm_key</b> parameter is the base segment ID for the database
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environment.</ul>
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<br>
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<br><b>Errors</b>
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<p>The DB_ENV->set_shm_key method
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may fail and return one of the following non-zero errors:</p>
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<br>
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<b>EINVAL</b><ul compact><li>If the method was called after <a href="../api_c/env_open.html">DB_ENV->open</a> was called; or if an
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invalid flag value or parameter was specified.</ul>
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<br>
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<hr size=1 noshade>
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<b>Description: DB_ENV->get_shm_key</b>
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<p>The DB_ENV->get_shm_key method returns the base segment ID.</p>
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<p>The DB_ENV->get_shm_key method may be called at any time during the life of the
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application.</p>
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<p>The DB_ENV->get_shm_key method
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returns a non-zero error value on failure
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and 0 on success.
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</p>
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<b>Parameters</b> <br>
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<b>shm_keyp</b><ul compact><li>The DB_ENV->get_shm_key method returns the
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base segment ID in <b>shm_keyp</b>.</ul>
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<br>
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<hr size=1 noshade>
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<br><b>Class</b>
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<a href="../api_c/env_class.html">DB_ENV</a>
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<br><b>See Also</b>
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<a href="../api_c/env_list.html">Database Environments and Related Methods</a>
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</tt>
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<table width="100%"><tr><td><br></td><td align=right>
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<a href="../api_c/api_core.html"><img src="../images/api.gif" alt="API"></a><a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a>
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</td></tr></table>
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<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font>
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