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189 lines
7.7 KiB
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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>DbEnv::set_mp_mmapsize()</title>
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<link rel="stylesheet" href="apiReference.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Berkeley DB C++ API Reference" />
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<link rel="up" href="memp.html" title="Chapter 9. The DbMpoolFile Handle" />
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<link rel="prev" href="mempset_mp_max_write.html" title="DbEnv::set_mp_max_write()" />
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<link rel="next" href="envset_mp_mtxcount.html" title="DbEnv::set_mp_mtxcount()" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 11.2.5.2</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">DbEnv::set_mp_mmapsize()</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="mempset_mp_max_write.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 9.
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The DbMpoolFile Handle
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="envset_mp_mtxcount.html">Next</a></td>
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</tr>
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</table>
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<hr />
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="envset_mp_mmapsize"></a>DbEnv::set_mp_mmapsize()</h2>
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</div>
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</div>
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</div>
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<pre class="programlisting">#include <db_cxx.h>
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int
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DbEnv::set_mp_mmapsize(size_t mp_mmapsize); </pre>
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<p>
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Files that are opened read-only in the cache (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
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result in immense process sizes in the presence of large databases.
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</p>
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<p>
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The <code class="methodname">DbEnv::set_mp_mmapsize()</code> method sets the maximum file size, in
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bytes, for a file to be mapped into the process address space. If no
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value is specified, it defaults to 10MB.
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</p>
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<p>
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The database environment's maximum mapped file size may also be
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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
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the entry in that file is a single line with the string
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"set_mp_mmapsize", one or more whitespace characters, and the size
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in bytes. 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
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environment is opened, it will silently overrule configuration
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done before that time.
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</p>
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<p>
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The <code class="methodname">DbEnv::set_mp_mmapsize()</code> method configures a database
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environment, not only operations performed using the specified
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<a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a> handle.
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</p>
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<p>
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The <code class="methodname">DbEnv::set_mp_mmapsize()</code> method may be called at any time during
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the life of the application.
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</p>
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<p>
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The <code class="methodname">DbEnv::set_mp_mmapsize()</code> <span>
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<span>
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method either returns a non-zero error value or throws an
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exception that encapsulates a non-zero error value on
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failure, and returns 0 on success.
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</span>
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</span>
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</p>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="id3647167"></a>Parameters</h3>
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</div>
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</div>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="id3647156"></a>mp_mmapsize</h4>
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</div>
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</div>
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</div>
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<p>
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The <span class="bold"><strong>mp_mmapsize</strong></span> parameter is the
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maximum file size, in bytes, for a file to be mapped into the process
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address space.
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</p>
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</div>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="id3646616"></a>Errors</h3>
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</div>
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</div>
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</div>
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<p>
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The <code class="methodname">DbEnv::set_mp_mmapsize()</code> <span>
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<span>
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method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a>
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exception, encapsulating one of the following non-zero errors, or return one
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of the following non-zero errors:
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</span>
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</span>
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</p>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="id3647318"></a>EINVAL</h4>
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</div>
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</div>
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</div>
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<p>
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An invalid flag value or parameter was specified.
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</p>
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</div>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="id3647297"></a>Class</h3>
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</div>
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</div>
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</div>
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<p>
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<a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a>,
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<a class="link" href="memp.html" title="Chapter 9. The DbMpoolFile Handle">DbMpoolFile</a>
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</p>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="id3647340"></a>See Also</h3>
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</div>
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</div>
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</div>
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<p>
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<a class="xref" href="memp.html#memplist" title="Memory Pools and Related Methods">Memory Pools and Related Methods</a>
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</p>
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</div>
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</div>
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<div class="navfooter">
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<hr />
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<table width="100%" summary="Navigation footer">
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<tr>
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<td width="40%" align="left"><a accesskey="p" href="mempset_mp_max_write.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="memp.html">Up</a>
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</td>
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|||
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<td width="40%" align="right"> <a accesskey="n" href="envset_mp_mtxcount.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">DbEnv::set_mp_max_write() </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> DbEnv::set_mp_mtxcount()</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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