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HTML
203 lines
8.7 KiB
HTML
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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>DB_ENV->set_shm_key()</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="env.html" title="Chapter 5. The DB_ENV Handle" />
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<link rel="prev" href="envset_msgfile.html" title="DB_ENV->set_msgfile()" />
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<link rel="next" href="envset_thread_count.html" title="DB_ENV->set_thread_count()" />
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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">DB_ENV->set_shm_key()</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="envset_msgfile.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 5.
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The DB_ENV Handle
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="envset_thread_count.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="envset_shm_key"></a>DB_ENV->set_shm_key()</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_ENV->set_shm_key(DB_ENV *dbenv, long shm_key); </pre>
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<p>
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Specify a base segment ID for Berkeley DB environment shared memory
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regions created in system memory on VxWorks or systems supporting
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X/Open-style shared memory interfaces; for example, UNIX systems
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supporting <span class="bold"><strong>shmget</strong></span>(2) and related
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System V IPC interfaces.
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</p>
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<p>
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This base segment ID will be used when Berkeley DB shared memory
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regions are first created. It will be incremented a small integer
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value each time a new shared memory region is created; that is, if the
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base ID is 35, the first shared memory region created will have a
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segment ID of 35, and the next one will have a segment ID between 36
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and 40 or so. A Berkeley DB environment always creates a master
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shared memory region; an additional shared memory region for each of
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the subsystems supported by the environment (Locking, Logging, Memory
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Pool and Transaction); plus an additional shared memory region for
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each additional memory pool cache that is supported. Already existing
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regions with the same segment IDs will be removed. See
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<a href="../../programmer_reference/env_region.html" class="olink">Shared Memory Regions</a>
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for more information.
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</p>
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<p>
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The intent behind this method is two-fold: without it, applications
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have no way to ensure that two Berkeley DB applications don't attempt
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to use the same segment IDs when creating different Berkeley DB
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environments. In addition, by using the same segment IDs each time
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the environment is created, previously created segments will be
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removed, and the set of segments on the system will not grow without
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bound.
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</p>
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<p>
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The database environment's base segment ID may also be configured
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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
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in that file is a single line with the string "set_shm_key", one
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or more whitespace characters, and the ID. Because the <a href="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class="olink">DB_CONFIG</a>
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file is read when the database environment is opened, it will
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silently overrule configuration done before that time.
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</p>
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<p>
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The <code class="methodname">DB_ENV->set_shm_key()</code> method configures operations performed
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using the specified <a class="link" href="env.html" title="Chapter 5. The DB_ENV Handle">DB_ENV</a> handle, not all
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operations performed on the underlying database environment.
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</p>
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<p>
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The <code class="methodname">DB_ENV->set_shm_key()</code> method may not be called after the
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<a class="xref" href="envopen.html" title="DB_ENV->open()">DB_ENV->open()</a> method is called.
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If the database environment already exists when
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<a class="xref" href="envopen.html" title="DB_ENV->open()">DB_ENV->open()</a> is called, the
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information specified to <code class="methodname">DB_ENV->set_shm_key()</code> must be consistent
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with the existing environment or corruption can occur.
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</p>
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<p>
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The <code class="methodname">DB_ENV->set_shm_key()</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="id3897197"></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="id3897186"></a>shm_key</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>shm_key</strong></span> parameter is the base
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segment ID for the database environment.
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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="id3896954"></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_ENV->set_shm_key()</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="id3897359"></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 method was called after <a class="xref" href="envopen.html" title="DB_ENV->open()">DB_ENV->open()</a>
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was called; or if 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="id3897183"></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>
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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="id3897232"></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="env.html#envlist" title="Database Environments and Related Methods">Database Environments 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="envset_msgfile.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="env.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="envset_thread_count.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_ENV->set_msgfile() </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_ENV->set_thread_count()</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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