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<b>DB->set_cachesize</b>
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<tt>
<b><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></b>
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<b>Description: DB->set_cachesize</b>
<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 maximum size of a single cache is 4GB on 32-bit
systems and 10TB on 64-bit systems. (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 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 split across <b>ncache</b> separate regions, where the
<b>region size</b> is equal to the initial cache size divided by
<b>ncache</b>.</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>
<b>Parameters</b> <br>
<b>bytes</b><ul compact><li>The size of the cache is set to <b>gbytes</b> gigabytes plus <b>bytes</b>.</ul>
<b>gbytes</b><ul compact><li>The size of the cache is set to <b>gbytes</b> gigabytes plus <b>bytes</b>.</ul>
<b>ncache</b><ul compact><li>The <b>ncache</b> parameter is the number of caches to create.</ul>
<br>
<br><b>Errors</b>
<p>The DB->set_cachesize method
may fail and return one of the following non-zero errors:</p>
<br>
<b>EINVAL</b><ul compact><li>If the specified cache size was impossibly small;
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.</ul>
<br>
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<b>Description: DB->get_cachesize</b>
<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>
<b>Parameters</b> <br>
<b>bytesp</b><ul compact><li>The <b>bytesp</b> parameter references memory into which
the additional bytes of memory in the cache is copied.</ul>
<b>gbytesp</b><ul compact><li>The <b>gbytesp</b> parameter references memory into which
the gigabytes of memory in the cache is copied.</ul>
<b>ncachep</b><ul compact><li>The <b>ncachep</b> parameter references memory into which
the number of caches is copied.</ul>
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<br><b>Class</b>
<a href="../api_c/db_class.html">DB</a>
<br><b>See Also</b>
<a href="../api_c/db_list.html">Databases and Related Methods</a>
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