<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> <title>Db::set_cachesize()</title> <link rel="stylesheet" href="apiReference.css" type="text/css" /> <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> <link rel="start" href="index.html" title="Berkeley DB C++ API Reference" /> <link rel="up" href="db.html" title="Chapter 2. The Db Handle" /> <link rel="prev" href="dbset_bt_prefix.html" title="Db::set_bt_prefix()" /> <link rel="next" href="dbset_create_dir.html" title="Db::set_create_dir()" /> </head> <body> <div xmlns="" class="navheader"> <div class="libver"> <p>Library Version 11.2.5.3</p> </div> <table width="100%" summary="Navigation header"> <tr> <th colspan="3" align="center">Db::set_cachesize()</th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="dbset_bt_prefix.html">Prev</a> </td> <th width="60%" align="center">Chapter 2. The Db Handle </th> <td width="20%" align="right"> <a accesskey="n" href="dbset_create_dir.html">Next</a></td> </tr> </table> <hr /> </div> <div class="sect1" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h2 class="title" style="clear: both"><a id="dbset_cachesize"></a>Db::set_cachesize()</h2> </div> </div> </div> <pre class="programlisting">#include <db_cxx.h> int Db::set_cachesize(u_int32_t gbytes, u_int32_t bytes, int ncache); </pre> <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="../../programmer_reference/general_am_conf.html#am_conf_cachesize" class="olink">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 <span class="bold"><strong>ncache</strong></span> is 0 or 1, the cache will be allocated contiguously in memory. If it is greater than 1, the cache will be split across <span class="bold"><strong>ncache</strong></span> separate regions, where the <span class="bold"><strong>region size</strong></span> is equal to the initial cache size divided by <span class="bold"><strong>ncache</strong></span>. </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 <code class="methodname">Db::set_cachesize()</code> method may not be called after the <a class="xref" href="dbopen.html" title="Db::open()">Db::open()</a> method is called. </p> <p> The <code class="methodname">Db::set_cachesize()</code> <span> <span> method either returns a non-zero error value or throws an exception that encapsulates a non-zero error value on failure, and returns 0 on success. </span> </span> </p> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="idp3174800"></a>Parameters</h3> </div> </div> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp2347048"></a>gbytes</h4> </div> </div> </div> <p> The size of the cache is set to <span class="bold"><strong>gbytes</strong></span> gigabytes plus <span class="bold"><strong>bytes</strong></span>. </p> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp2621672"></a>bytes</h4> </div> </div> </div> <p> The size of the cache is set to <span class="bold"><strong>gbytes</strong></span> gigabytes plus <span class="bold"><strong>bytes</strong></span>. </p> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp1624712"></a>ncache</h4> </div> </div> </div> <p> The <span class="bold"><strong>ncache</strong></span> parameter is the number of caches to create. </p> </div> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="idp1683024"></a>Errors</h3> </div> </div> </div> <p> The <code class="methodname">Db::set_cachesize()</code> <span> <span> method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a> exception, encapsulating one of the following non-zero errors, or return one of the following non-zero errors: </span> </span> </p> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp1284376"></a>EINVAL</h4> </div> </div> </div> <p> If the specified cache size was impossibly small; the method was called after <a class="xref" href="dbopen.html" title="Db::open()">Db::open()</a> was called; or if an invalid flag value or parameter was specified. </p> </div> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="idp2903280"></a>Class</h3> </div> </div> </div> <p> <a class="link" href="db.html" title="Chapter 2. The Db Handle">Db</a> </p> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="idp1800448"></a>See Also</h3> </div> </div> </div> <p> <a class="xref" href="db.html#dblist" title="Database and Related Methods">Database and Related Methods</a> </p> </div> </div> <div class="navfooter"> <hr /> <table width="100%" summary="Navigation footer"> <tr> <td width="40%" align="left"><a accesskey="p" href="dbset_bt_prefix.html">Prev</a> </td> <td width="20%" align="center"> <a accesskey="u" href="db.html">Up</a> </td> <td width="40%" align="right"> <a accesskey="n" href="dbset_create_dir.html">Next</a></td> </tr> <tr> <td width="40%" align="left" valign="top">Db::set_bt_prefix() </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> Db::set_create_dir()</td> </tr> </table> </div> </body> </html>