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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>DB_ENV->set_cachesize()</title>
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<p>Library Version 11.2.5.3</p>
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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_cachesize()</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_cache_max.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="mempset_mp_max_openfd.html">Next</a></td>
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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_cachesize"></a>DB_ENV->set_cachesize()</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_cachesize(DB_ENV *dbenv,
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u_int32_t gbytes, u_int32_t bytes, int ncache); </pre>
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<p>
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Sets the size of the shared memory buffer pool — that is, the cache.
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The cache should be the size of the normal working data set of the
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application, with some small amount of additional memory for unusual
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situations. (Note: the working set is not the same as the number of
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pages accessed simultaneously, and is usually much larger.)
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</p>
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<p>
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The default cache size is 256KB, and may not be specified as less than
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20KB. Any cache size less than 500MB is automatically increased by
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25% to account for cache overhead; cache sizes larger than 500MB
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are used as specified. The maximum size of a single cache is 4GB on
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32-bit systems and 10TB on 64-bit systems. (All sizes are in
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powers-of-two, that is, 256KB is 2^18 not 256,000.) For information on
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tuning the Berkeley DB cache size, see
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<a href="../../programmer_reference/general_am_conf.html#am_conf_cachesize" class="olink">Selecting a cache size</a>.
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</p>
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<p>
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It is possible to specify caches to Berkeley DB large enough they
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cannot be allocated contiguously on some architectures. For example,
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some releases of Solaris limit the amount of memory that may be
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allocated contiguously by a process. If <span class="bold"><strong>ncache</strong></span> is 0 or 1, the cache will be allocated
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contiguously in memory. If it is greater than 1, the cache will be
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split across <span class="bold"><strong>ncache</strong></span> separate regions,
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where the <span class="bold"><strong>region size</strong></span> is equal to the
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initial cache size divided by <span class="bold"><strong>ncache</strong></span>.
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</p>
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<p>
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The cache may be resized by calling <code class="methodname">DB_ENV->set_cachesize()</code>
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after the environment is open. The supplied size will be rounded to the nearest multiple
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of the region size and may not be larger than the maximum size configured with
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<a class="xref" href="envset_cache_max.html" title="DB_ENV->set_cache_max()">DB_ENV->set_cache_max()</a>. The
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<span class="bold"><strong>ncache</strong></span> parameter is ignored when resizing the cache.
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</p>
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<p>
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The database environment's initial cache 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_cachesize", one or more whitespace characters, and the
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initial cache size specified in three parts: the gigabytes of
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cache, the additional bytes of cache, and the number of caches,
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also separated by whitespace characters. For example,
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"set_cachesize 2 524288000 3" would create a 2.5GB logical cache,
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split between three physical caches. Because the <a href="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class="olink">DB_CONFIG</a> file
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is read when the database environment is opened, it will silently
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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_cachesize()</code> method configures a database environment,
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not only operations performed using the specified <a class="link" href="env.html" title="Chapter 5. The DB_ENV Handle">DB_ENV</a> handle.
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</p>
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<p>
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The <code class="methodname">DB_ENV->set_cachesize()</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">DB_ENV->set_cachesize()</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="idp61303408"></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="idp61291232"></a>gbytes</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 size of the cache is set to <span class="bold"><strong>gbytes</strong></span> gigabytes plus <span class="bold"><strong>bytes</strong></span>.
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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="idp61310112"></a>bytes</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 size of the cache is set to <span class="bold"><strong>gbytes</strong></span> gigabytes plus <span class="bold"><strong>bytes</strong></span>.
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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="idp61297104"></a>ncache</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>ncache</strong></span> parameter is the number of
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caches to create.
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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="idp61317088"></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_cachesize()</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="idp61321800"></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 specified cache size was impossibly small; 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>
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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="idp61319712"></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="idp61323136"></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_cache_max.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="mempset_mp_max_openfd.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_cache_max() </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_mp_max_openfd()</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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