94 lines
4.2 KiB
HTML
94 lines
4.2 KiB
HTML
<!--$Id: env_set_mp_mmapsize.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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<!--See the file LICENSE for redistribution information.-->
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<html>
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<head>
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<title>Berkeley DB: DB_ENV->set_mp_mmapsize</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_mp_mmapsize</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_mp_mmapsize(DB_ENV *dbenv, size_t mp_mmapsize);
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<p>
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int
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DB_ENV->get_mp_mmapsize(DB_ENV *dbenv, size_t *mp_mmapsizep);
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</pre></b>
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<hr size=1 noshade>
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<b>Description: DB_ENV->set_mp_mmapsize</b>
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<p>Files that are opened read-only in the pool (and that satisfy a few
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other criteria) are, by default, mapped into the process address space
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instead of being copied into the local cache. This can result in
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better-than-usual performance because available virtual memory is
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normally much larger than the local cache, and page faults are faster
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than page copying on many systems. However, it can cause resource
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starvation in the presence of limited virtual memory, and it can result
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in immense process sizes in the presence of large databases.</p>
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<p>The DB_ENV->get_mp_mmapsize method sets the maximum file size, in bytes,
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for a file to be mapped into the process address space. If no value is
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specified, it defaults to 10MB.</p>
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<p>The database environment's maximum mapped file size 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_mp_mmapsize", one or more whitespace
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characters, and the size in bytes.
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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_mp_mmapsize method configures a database environment, not only operations
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performed using the specified <a href="../api_c/env_class.html">DB_ENV</a> handle.</p>
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<p>The DB_ENV->set_mp_mmapsize 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->set_mp_mmapsize 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>mp_mmapsize</b><ul compact><li>The <b>mp_mmapsize</b> parameter is the maximum file size, in bytes,
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for a file to be mapped into the process address space.</ul>
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<br>
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<br><b>Errors</b>
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<p>The DB_ENV->set_mp_mmapsize 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_mp_mmapsize</b>
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<p>The DB_ENV->get_mp_mmapsize method returns the maximum file map size.</p>
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<p>The DB_ENV->get_mp_mmapsize 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_mp_mmapsize 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>mp_mmapsizep</b><ul compact><li>The DB_ENV->get_mp_mmapsize method returns the
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maximum file map size in <b>mp_mmapsizep</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>, <a href="../api_c/mempfile_class.html">DB_MPOOLFILE</a>
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<br><b>See Also</b>
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<a href="../api_c/memp_list.html">Memory Pools 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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</body>
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</html>
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