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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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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>DB_MPOOLFILE->open()</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 8. The DB_MPOOLFILE Handle" />
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<link rel="prev" href="mempfget.html" title="DB_MPOOLFILE->get()" />
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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 11.2.5.3</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">DB_MPOOLFILE->open()</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="mempfget.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 8.
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The DB_MPOOLFILE Handle
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="mempput.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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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="mempfopen"></a>DB_MPOOLFILE->open()</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.h>
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int
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DB_MPOOLFILE->open(DB_MPOOLFILE *mpf,
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char *file, u_int32_t flags, int mode, size_t pagesize); </pre>
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<p>
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The <code class="methodname">DB_MPOOLFILE->open()</code> method opens a file in the in-memory cache.
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</p>
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<p>
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The <code class="methodname">DB_MPOOLFILE->open()</code> <span>
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<span>
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method returns a non-zero error value on failure and 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="idp61413992"></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="idp61421336"></a>file</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>file</strong></span> parameter is the name of the
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file to be opened. If <span class="bold"><strong>file</strong></span> is NULL,
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a private temporary file is created that cannot be shared with any
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other process (although it may be shared with other threads of control
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in the same process).
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</p>
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<p>
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When using a Unicode build on Windows (the default), the
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<span class="bold"><strong>file</strong></span> argument will
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be interpreted as a UTF-8 string, which is equivalent to ASCII for Latin
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characters.
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</p>
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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="idp61403432"></a>flags</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>flags</strong></span> parameter must be set to zero or
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by bitwise inclusively <span class="bold"><strong>OR</strong></span>'ing together one
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or more of the following values:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p><a id="mempopen_DB_CREATE"></a>
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<code class="literal">DB_CREATE</code>
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</p>
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<p>
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Create any underlying files, as necessary. If the database do not already exist
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and the <code class="literal">DB_CREATE</code> flag is not specified, the
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call will fail.
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</p>
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</li>
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<li>
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<p><a id="mempopen_DB_EXCL"></a>
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<code class="literal">DB_DIRECT</code>
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</p>
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<p>
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If set and supported by the system, turn off system buffering of the file to
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avoid double caching.
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</p>
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</li>
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<li>
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<p><a id="mempopen_DB_MULTIVERSION"></a>
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<code class="literal">DB_MULTIVERSION</code>
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</p>
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<p>
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Open the file with support for
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<a href="../../programmer_reference/transapp_read.html" class="olink">multiversion concurrency control</a>.
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Calls to <a class="xref" href="mempfget.html" title="DB_MPOOLFILE->get()">DB_MPOOLFILE->get()</a>
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with dirty pages will cause copies to be made in the cache.
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</p>
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</li>
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<li>
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<p><a id="mempopen_DB_NOMMAP"></a>
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<code class="literal">DB_NOMMAP</code>
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</p>
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<p>
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Always copy this file into the local cache instead of potentially mapping it
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into process memory (see the
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<a class="xref" href="envset_mp_mmapsize.html" title="DB_ENV->set_mp_mmapsize()">DB_ENV->set_mp_mmapsize()</a>
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method for further information).
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</p>
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</li>
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<li>
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<p><a id="mempopen_DB_ODDFILESIZE"></a>
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<code class="literal">DB_ODDFILESIZE</code>
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</p>
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<p>
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Attempts to open files which are not a multiple of the page size in length will
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fail, by default. If the DB_ODDFILESIZE flag is set, any partial page at the end
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of the file will be ignored and the open will proceed.
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</p>
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</li>
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<li>
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<p><a id="mempopen_DB_RDONLY"></a>
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<code class="literal">DB_RDONLY</code>
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</p>
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<p>
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Open any underlying files for reading only. Any attempt to modify
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the file using the memory pool (cache) functions will fail, regardless of the actual
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permissions of the file.
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</p>
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</li>
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</ul>
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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="idp61438656"></a>mode</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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On Windows systems, the mode parameter is ignored.
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</p>
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<p>
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On UNIX systems or in IEEE/ANSI Std 1003.1 (POSIX) environments, files
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created by <code class="methodname">DB_MPOOLFILE->open()</code> are created with mode
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<span class="bold"><strong>mode</strong></span> (as described in <span class="bold"><strong>chmod</strong></span>(2)) and modified by the process' umask
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value at the time of creation (see <span class="bold"><strong>umask</strong></span>(2)). Created files are owned by the
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process owner; the group ownership of created files is based on the system
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and directory defaults, and is not further specified by Berkeley DB. System
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shared memory segments created by <code class="methodname">DB_MPOOLFILE->open()</code> are
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created with mode <span class="bold"><strong>mode</strong></span>, unmodified by the
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process' umask value. If <span class="bold"><strong>mode</strong></span> is 0,
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<code class="methodname">DB_MPOOLFILE->open()</code> will use a default mode of readable
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and writable by both owner and group.
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</p>
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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="idp61437920"></a>pagesize</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>pagesize</strong></span> parameter is the size,
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in bytes, of the unit of transfer between the application and the
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cache, although it is not necessarily the unit of transfer between the
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cache and the underlying filesystem.
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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="idp61384616"></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">DB_MPOOLFILE->open()</code> <span>
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<span>
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method may fail and return one 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="idp61434488"></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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If the file has already been entered into the cache, and the <span class="bold"><strong>pagesize</strong></span> value is not the same as when the file
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was entered into the cache, or the length of the file is not zero or a
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multiple of the <span class="bold"><strong>pagesize</strong></span>; the
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DB_RDONLY flag was specified for an in-memory cache; or if an invalid
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flag value or parameter was specified.
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</p>
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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="idp61435632"></a>ENOMEM</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 maximum number of open files has been reached.
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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="idp61431568"></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 DB_ENV Handle">DB_ENV</a>, <a class="link" href="memp.html" title="Chapter 8. The DB_MPOOLFILE Handle">DB_MPOOLFILE</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="idp61436712"></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="mempfget.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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<td width="40%" align="right"> <a accesskey="n" href="mempput.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">DB_MPOOLFILE->get() </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"> DB_MPOOLFILE->put()</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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