<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>DbEnv::set_mp_mmapsize()</title>
<link rel="stylesheet" href="apiReference.css" type="text/css" />
<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
<link rel="start" href="index.html" title="Berkeley DB C++ API Reference" />
<link rel="up" href="memp.html" title="Chapter 9. The DbMpoolFile Handle" />
<link rel="prev" href="mempset_mp_max_write.html" title="DbEnv::set_mp_max_write()" />
<link rel="next" href="mempfclose.html" title="DbMpoolFile::close()" />
</head>
<body>
<div class="navheader">
<table width="100%" summary="Navigation header">
<tr>
<th colspan="3" align="center">DbEnv::set_mp_mmapsize()</th>
</tr>
<tr>
<td width="20%" align="left"><a accesskey="p" href="mempset_mp_max_write.html">Prev</a> </td>
<th width="60%" align="center">Chapter 9.
The DbMpoolFile Handle
</th>
<td width="20%" align="right"> <a accesskey="n" href="mempfclose.html">Next</a></td>
</tr>
</table>
<hr />
</div>
<div class="sect1" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both"><a id="envset_mp_mmapsize"></a>DbEnv::set_mp_mmapsize()</h2>
</div>
</div>
</div>
<pre class="programlisting">#include <db_cxx.h>
int
DbEnv::set_mp_mmapsize(size_t mp_mmapsize); </pre>
<p>
Files that are opened read-only in the cache (and that satisfy a few
other criteria) are, by default, mapped into the process address space
instead of being copied into the local cache. This can result in
better-than-usual performance because available virtual memory is
normally much larger than the local cache, and page faults are faster
than page copying on many systems. However, it can cause resource
starvation in the presence of limited virtual memory, and it can
result in immense process sizes in the presence of large databases.
</p>
<p>
The <code class="methodname">DbEnv::set_mp_mmapsize()</code> method sets the maximum file size, in
bytes, for a file to be mapped into the process address space. If no
value is specified, it defaults to 10MB.
</p>
<p>
The database environment's maximum mapped file size may also be
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 the entry in that file is a single line with the string
"set_mp_mmapsize", one or more whitespace characters, and the size 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 environment is opened, it will silently
overrule configuration done before that time.
</p>
<p>
The <code class="methodname">DbEnv::set_mp_mmapsize()</code> method configures a database
environment, not only operations performed using the specified
<a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a> handle.
</p>
<p>
The <code class="methodname">DbEnv::set_mp_mmapsize()</code> method may be called at any time during
the life of the application.
</p>
<p>
The <code class="methodname">DbEnv::set_mp_mmapsize()</code> <span>
<span>
method either returns a non-zero error value or throws an
exception that encapsulates a non-zero error value on
failure, and returns 0 on success.
</span>
</span>
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1693260"></a>Parameters</h3>
</div>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1693422"></a>mp_mmapsize</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>mp_mmapsize</strong></span> parameter is the
maximum file size, in bytes, for a file to be mapped into the process
address space.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1693261"></a>Errors</h3>
</div>
</div>
</div>
<p>
The <code class="methodname">DbEnv::set_mp_mmapsize()</code> <span>
<span>
method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a>
exception, encapsulating one of the following non-zero errors, or return one
of the following non-zero errors:
</span>
</span>
</p>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1693396"></a>EINVAL</h4>
</div>
</div>
</div>
<p>
An invalid flag value or parameter was specified.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1693395"></a>Class</h3>
</div>
</div>
</div>
<p>
<a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a>,
<a class="link" href="memp.html" title="Chapter 9. The DbMpoolFile Handle">DbMpoolFile</a>
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1693525"></a>See Also</h3>
</div>
</div>
</div>
<p>
<a class="xref" href="memp.html#memplist" title="Memory Pools and Related Methods">Memory Pools and Related Methods</a>
</p>
</div>
</div>
<div class="navfooter">
<hr />
<table width="100%" summary="Navigation footer">
<tr>
<td width="40%" align="left"><a accesskey="p" href="mempset_mp_max_write.html">Prev</a> </td>
<td width="20%" align="center">
<a accesskey="u" href="memp.html">Up</a>
</td>
<td width="40%" align="right"> <a accesskey="n" href="mempfclose.html">Next</a></td>
</tr>
<tr>
<td width="40%" align="left" valign="top">DbEnv::set_mp_max_write() </td>
<td width="20%" align="center">
<a accesskey="h" href="index.html">Home</a>
</td>
<td width="40%" align="right" valign="top"> DbMpoolFile::close()</td>
</tr>
</table>
</div>
</body>
</html>
