2011-09-13 17:44:24 +00:00
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<title>Db::set_cachesize()</title>
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<p>Library Version 11.2.5.2</p>
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<th colspan="3" align="center">Db::set_cachesize()</th>
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<td width="20%" align="left"><a accesskey="p" href="dbset_bt_prefix.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 2.
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The Db Handle
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<h2 class="title" style="clear: both"><a id="dbset_cachesize"></a>Db::set_cachesize()</h2>
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<pre class="programlisting">#include <db_cxx.h>
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int
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Db::set_cachesize(u_int32_t gbytes, u_int32_t bytes, int ncache); </pre>
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<p>
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Set 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 buffer pool 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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Because databases opened within Berkeley DB environments use the cache
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specified to the environment, it is an error to attempt to set a cache
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in a database created within an environment.
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</p>
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<p>
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The <code class="methodname">Db::set_cachesize()</code> method may not be called after the
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<a class="xref" href="dbopen.html" title="Db::open()">Db::open()</a> method is called.
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</p>
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<p>
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The <code class="methodname">Db::set_cachesize()</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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2011-12-20 00:07:10 +00:00
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<h3 class="title"><a id="id3573163"></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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2011-12-20 00:07:10 +00:00
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<h4 class="title"><a id="id3573410"></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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2011-12-20 00:07:10 +00:00
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<h4 class="title"><a id="id3573560"></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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2011-12-20 00:07:10 +00:00
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<h4 class="title"><a id="id3573304"></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
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the number of 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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2011-12-20 00:07:10 +00:00
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<h3 class="title"><a id="id3573653"></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::set_cachesize()</code> <span>
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<span>
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method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a>
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exception, encapsulating one of the following non-zero errors, or return one
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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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2011-12-20 00:07:10 +00:00
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<h4 class="title"><a id="id3573791"></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; the method was
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called after <a class="xref" href="dbopen.html" title="Db::open()">Db::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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2011-12-20 00:07:10 +00:00
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<h3 class="title"><a id="id3573726"></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="db.html" title="Chapter 2. The Db Handle">Db</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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2011-12-20 00:07:10 +00:00
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<h3 class="title"><a id="id3573635"></a>See Also</h3>
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2011-09-13 17:44:24 +00:00
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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="db.html#dblist" title="Database and Related Methods">Database and Related Methods</a>
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</p>
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<td width="40%" align="right"> <a accesskey="n" href="dbset_create_dir.html">Next</a></td>
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<a accesskey="h" href="index.html">Home</a>
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<td width="40%" align="right" valign="top"> Db::set_create_dir()</td>
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