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<!--$Id: db_set_cachesize.so,v 10.21 2002/08/18 21:15:53 bostic Exp $-->
<!--$Id: env_set_cachesize.so,v 10.49 2004/09/28 15:04:20 bostic Exp $-->
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<title>Berkeley DB: DB->set_cachesize</title>
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<h3>DB->set_cachesize</h3>
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<tt>
<h3><pre>
#include <db.h>
<p>
int
DB->set_cachesize(DB *db,
u_int32_t gbytes, u_int32_t bytes, int ncache);
<p>
int
DB->get_cachesize(DB *db,
u_int32_t *gbytesp, u_int32_t *bytesp, int *ncachep);
</pre></h3>
<hr size=1 noshade>
<h3>Description: DB->set_cachesize</h3>
<p>Set the size of the shared memory buffer pool -- that is, the cache.
The cache should be the size of the normal working data set of the
application, with some small amount of additional memory for unusual
situations. (Note: the working set is not the same as the number of
pages accessed simultaneously, and is usually much larger.)</p>
<p>The default cache size is 256KB, and may not be specified as less than
20KB. Any cache size less than 500MB is automatically increased by 25%
to account for buffer pool overhead; cache sizes larger than 500MB are
used as specified. The current maximum size of a single cache is 4GB.
(All sizes are in powers-of-two, that is, 256KB is 2^18 not 256,000.)
For information on tuning the Berkeley DB cache size, see
<a href="../ref/am_conf/cachesize.html">Selecting a cache size</a>.</p>
<p>It is possible to specify caches to Berkeley DB larger than 4GB and/or large
enough they cannot be allocated contiguously on some architectures. For
example, some releases of Solaris limit the amount of memory that may
be allocated contiguously by a process. If <b>ncache</b> is 0 or 1,
the cache will be allocated contiguously in memory. If it is greater
than 1, the cache will be broken up into <b>ncache</b> equally sized,
separate pieces of memory.</p>
<p>Because databases opened within Berkeley DB environments use the cache
specified to the environment, it is an error to attempt to set a cache
in a database created within an environment.</p>
<p>The DB->set_cachesize method may not be called after the <a href="../api_c/db_open.html">DB->open</a> method is called.
</p>
<p>The DB->set_cachesize method
returns a non-zero error value on failure
and 0 on success.
</p>
<h3>Parameters</h3>
<dl compact>
<dt><b>bytes</b><dd>The size of the cache is set to <b>gbytes</b> gigabytes plus <b>bytes</b>.
<dt><b>gbytes</b><dd>The size of the cache is set to <b>gbytes</b> gigabytes plus <b>bytes</b>.
<dt><b>ncache</b><dd>The <b>ncache</b> parameter is the number of caches to create.
</dl>
<h3>Errors</h3>
<p>The DB->set_cachesize method
may fail and return one of the following non-zero errors:</p>
<dl compact>
<dt>EINVAL<dd>If the specified cache size was impossibly small;
called in a database environment;
the method was called after
<a href="../api_c/db_open.html">DB->open</a>
was called; or if an
invalid flag value or parameter was specified.
</dl>
<hr size=1 noshade>
<h3>Description: DB->get_cachesize</h3>
<p>The DB->get_cachesize method returns the current size and composition of the
cache.</p>
<p>The DB->get_cachesize method may be called at any time during the life of the
application.</p>
<p>The DB->get_cachesize method
returns a non-zero error value on failure
and 0 on success.
</p>
<h3>Parameters</h3>
<dl compact>
<dt><b>bytesp</b><dd>The <b>bytesp</b> parameter references memory into which
the additional bytes of memory in the cache is copied.
<dt><b>gbytesp</b><dd>The <b>gbytesp</b> parameter references memory into which
the gigabytes of memory in the cache is copied.
<dt><b>ncachep</b><dd>The <b>ncachep</b> parameter references memory into which
the number of caches is copied.
</dl>
<hr size=1 noshade>
<h3>Class</h3>
<a href="../api_c/db_class.html">DB</a>
<h3>See Also</h3>
<a href="../api_c/db_list.html">Databases and Related Methods</a>
</tt>
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