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130 lines
6.5 KiB
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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>set_cachesize</title>
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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="configuration_reference.html" title="Appendix B. DB_CONFIG Parameter Reference" />
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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">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="repmgr_site_parameter.html">Prev</a> </td>
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<th width="60%" align="center">Appendix B. DB_CONFIG Parameter Reference</th>
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<td width="20%" align="right"> <a accesskey="n" href="set_cache_max_parameter.html">Next</a></td>
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</tr>
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</table>
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<hr />
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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="set_cachesize_parameter"></a>set_cachesize</h2>
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</div>
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</div>
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</div>
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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 value specified for this parameter is the
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<span class="emphasis"><em>maximum</em></span> value that your application
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will be able to use for your in-memory cache. If your
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application does not have enough data to fill up the amount
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of space specified here, then your application will only
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use the amount of memory required by the data that your
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application does have.
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</p>
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<p>
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For the DB, the default cache size is 8MB. You cannot specify a
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cache size value of less than 100KB.
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</p>
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<p>
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Any cache size less than 500MB is automatically increased
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by 25% to account for cache overhead; cache sizes larger
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than 500MB are used as specified. The maximum size of a
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single cache is 4GB on 32-bit systems and 10TB on 64-bit
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systems. (All sizes are in powers-of-two, that is, 256KB
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is 2^18 not 256,000.)
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</p>
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<p>
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It is possible to specify cache sizes 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 size supplied to this parameter will be
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rounded to the nearest multiple of the region size and may not
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be larger than the maximum possible cache size configured for your
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application (use the
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<a class="xref" href="set_cache_max_parameter.html" title="set_cache_max">set_cache_max</a>
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to do this). The <span class="bold"><strong>ncache</strong></span>
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parameter is ignored when resizing the cache.
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</p>
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<p>
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The syntax of this parameter in the <a href="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class="olink">DB_CONFIG</a> file is a
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single line with the string
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<code class="literal">set_cachesize</code>, one or more whitespace
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characters, and the initial cache size specified in three
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parts: the gigabytes of cache, the additional bytes of
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cache, and the number of caches, also separated by
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whitespace characters. For example:
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</p>
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<pre class="programlisting">set_cachesize 2 524288000 1</pre>
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<p>
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Creates a single 2.5GB physical cache.
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</p>
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<p>
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Note that this parameter is ignored unless it is specified
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before you initially create your environment, or you
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re-create your environment after changing it.
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</p>
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<p>
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For more information, see
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<a class="xref" href="envset_cachesize.html" title="DbEnv::set_cachesize()">DbEnv::set_cachesize()</a>.
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</p>
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</div>
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<div class="navfooter">
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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="repmgr_site_parameter.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="configuration_reference.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="set_cache_max_parameter.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">repmgr_site </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"> set_cache_max</td>
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</tr>
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</table>
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</div>
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</html>
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