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204 lines
9.1 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::memp_register()</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="mempfcreate.html" title="DbEnv::memp_fcreate()" />
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<link rel="next" href="mempstat.html" title="DbEnv::memp_stat()" />
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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::memp_register()</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="mempfcreate.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="mempstat.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="mempregister"></a>DbEnv::memp_register()</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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extern "C" {
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typedef int (*pgin_fcn_type)(DB_ENV *dbenv,
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db_pgno_t pgno, void *pgaddr, DBT *pgcookie);
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typedef int (*pgout_fcn_type)(DB_ENV *dbenv,
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db_pgno_t pgno, void *pgaddr, DBT *pgcookie);
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};
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int
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DbEnv::memp_register(int ftype,
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pgin_fcn_type pgin_fcn, pgout_fcn_type pgout_fcn);</pre>
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<p>
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The <code class="methodname">DbEnv::memp_register()</code> method registers page-in and page-out
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functions for files of type <span class="bold"><strong>ftype</strong></span> in the cache.
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</p>
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<p>
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If the <span class="bold"><strong>pgin_fcn</strong></span> function is non-NULL,
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it is called each time a page is read into the cache from a file
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of type <span class="bold"><strong>ftype</strong></span>, or a page is created
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for a file of type <span class="bold"><strong>ftype</strong></span> (see the
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DB_MPOOL_CREATE flag for the
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<a class="xref" href="mempfget.html" title="DbMpoolFile::get()">DbMpoolFile::get()</a> method).
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</p>
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<p>
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If the <span class="bold"><strong>pgout_fcn</strong></span> function is
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non-NULL, it is called each time a page is written to a file of type
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<span class="bold"><strong>ftype</strong></span>.
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</p>
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<p>
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The purpose of the <code class="methodname">DbEnv::memp_register()</code> function is to support
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processing when pages are entered into, or flushed from, the cache. For example, this
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functionality might be used to do byte-endian conversion as pages are read from, or written
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to, the underlying file.
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</p>
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<p>
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A file type must be specified to make it possible for unrelated
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threads or processes that are sharing a cache, to evict each other's
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pages from the cache. During initialization, applications should call
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<code class="methodname">DbEnv::memp_register()</code> for each type of file requiring input or
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output processing that will be sharing the underlying cache. (No
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registry is necessary for the standard Berkeley DB access method types
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because <a class="xref" href="dbopen.html" title="Db::open()">Db::open()</a>
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registers them separately.)
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</p>
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<p>
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If a thread or process does not call <code class="methodname">DbEnv::memp_register()</code> for a
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file type, it is impossible for it to evict pages for any file
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requiring input or output processing from the cache. For this reason,
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<code class="methodname">DbEnv::memp_register()</code> should always be called by each application
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sharing a cache for each type of file included in the cache, regardless
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of whether or not the application itself uses files of that type.
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</p>
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<p>
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The <code class="methodname">DbEnv::memp_register()</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="id3644276"></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="id3644266"></a>ftype</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>ftype</strong></span> parameter specifies the
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type of file for which the page-in and page-out functions will be
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called.
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</p>
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<p>
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The <span class="bold"><strong>ftype</strong></span> value for a file must be a
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non-zero positive number less than 128 (0 and negative numbers are
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reserved for internal use by the Berkeley DB library).
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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="id3644184"></a>pgin_fcn, pgout_fcn</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 page-in and page-out functions.
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</p>
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<p>
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The <span class="bold"><strong>pgin_fcn</strong></span> and <span class="bold"><strong>pgout_fcn</strong></span> functions are called with a reference
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to the current database environment, the page number being read or
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written, a pointer to the page being read or written, and any
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parameter <span class="bold"><strong>pgcookie</strong></span> that was specified
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to the <a class="xref" href="mempset_pgcookie.html" title="DbMpoolFile::set_pgcookie()">DbMpoolFile::set_pgcookie()</a>
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method.
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</p>
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<p>
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The <span class="bold"><strong>pgin_fcn</strong></span> and <span class="bold"><strong>pgout_fcn</strong></span> functions should return 0 on success,
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and a non-zero value on failure, in which case the shared Berkeley DB
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library function calling it will also fail, returning that non-zero
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value. The non-zero value should be selected from values outside of
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the Berkeley DB library namespace.
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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="id3644073"></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>, <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="id3644402"></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="mempfcreate.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="mempstat.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::memp_fcreate() </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::memp_stat()</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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