1<?xml version="1.0" encoding="UTF-8" standalone="no"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml"> 4 <head> 5 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> 6 <title>DB->set_cachesize()</title> 7 <link rel="stylesheet" href="apiReference.css" type="text/css" /> 8 <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> 9 <link rel="start" href="index.html" title="Berkeley DB C API Reference" /> 10 <link rel="up" href="db.html" title="Chapter��2.�� The DB Handle" /> 11 <link rel="prev" href="dbset_bt_prefix.html" title="DB->set_bt_prefix()" /> 12 <link rel="next" href="dbset_create_dir.html" title="DB->set_create_dir()" /> 13 </head> 14 <body> 15 <div class="navheader"> 16 <table width="100%" summary="Navigation header"> 17 <tr> 18 <th colspan="3" align="center">DB->set_cachesize()</th> 19 </tr> 20 <tr> 21 <td width="20%" align="left"><a accesskey="p" href="dbset_bt_prefix.html">Prev</a>��</td> 22 <th width="60%" align="center">Chapter��2.�� 23 The DB Handle 24 </th> 25 <td width="20%" align="right">��<a accesskey="n" href="dbset_create_dir.html">Next</a></td> 26 </tr> 27 </table> 28 <hr /> 29 </div> 30 <div class="sect1" lang="en" xml:lang="en"> 31 <div class="titlepage"> 32 <div> 33 <div> 34 <h2 class="title" style="clear: both"><a id="dbset_cachesize"></a>DB->set_cachesize()</h2> 35 </div> 36 </div> 37 </div> 38 <pre class="programlisting">#include <db.h> 39 40int 41DB->set_cachesize(DB *db, 42 u_int32_t gbytes, u_int32_t bytes, int ncache); </pre> 43 <p> 44 Set the size of the shared memory buffer pool -- that is, the cache. 45 The cache should be the size of the normal working data set of the 46 application, with some small amount of additional memory for unusual 47 situations. (Note: the working set is not the same as the number of 48 pages accessed simultaneously, and is usually much larger.) 49 </p> 50 <p> 51 The default cache size is 256KB, and may not be specified as less than 52 20KB. Any cache size less than 500MB is automatically increased by 53 25% to account for buffer pool overhead; cache sizes larger than 500MB 54 are used as specified. The maximum size of a single cache is 4GB on 55 32-bit systems and 10TB on 64-bit systems. (All sizes are in 56 powers-of-two, that is, 256KB is 2^18 not 256,000.) For information on 57 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>. 58 </p> 59 <p> 60 It is possible to specify caches to Berkeley DB large enough they 61 cannot be allocated contiguously on some architectures. For example, 62 some releases of Solaris limit the amount of memory that may be 63 allocated contiguously by a process. If <span class="bold"><strong>ncache</strong></span> is 0 or 1, the cache will be allocated 64 contiguously in memory. If it is greater than 1, the cache will be 65 split across <span class="bold"><strong>ncache</strong></span> separate regions, 66 where the <span class="bold"><strong>region size</strong></span> is equal to the 67 initial cache size divided by <span class="bold"><strong>ncache</strong></span>. 68 </p> 69 <p> 70 Because databases opened within Berkeley DB environments use the cache 71 specified to the environment, it is an error to attempt to set a cache 72 in a database created within an environment. 73 </p> 74 <p> 75 The <code class="methodname">DB->set_cachesize()</code> method may not be called after the 76 <a class="xref" href="dbopen.html" title="DB->open()">DB->open()</a> method is called. 77 </p> 78 <p> 79 The <code class="methodname">DB->set_cachesize()</code> <span> 80 <span> 81 method returns a non-zero error value on failure and 0 on success. 82 </span> 83 84 </span> 85 </p> 86 <div class="sect2" lang="en" xml:lang="en"> 87 <div class="titlepage"> 88 <div> 89 <div> 90 <h3 class="title"><a id="id1644406"></a>Parameters</h3> 91 </div> 92 </div> 93 </div> 94 <div class="sect3" lang="en" xml:lang="en"> 95 <div class="titlepage"> 96 <div> 97 <div> 98 <h4 class="title"><a id="id1644378"></a>bytes</h4> 99 </div> 100 </div> 101 </div> 102 <p> 103 The size of the cache is set to <span class="bold"><strong>gbytes</strong></span> gigabytes plus <span class="bold"><strong>bytes</strong></span>. 104 </p> 105 </div> 106 <div class="sect3" lang="en" xml:lang="en"> 107 <div class="titlepage"> 108 <div> 109 <div> 110 <h4 class="title"><a id="id1644629"></a>gbytes</h4> 111 </div> 112 </div> 113 </div> 114 <p> 115 The size of the cache is set to <span class="bold"><strong>gbytes</strong></span> gigabytes plus <span class="bold"><strong>bytes</strong></span>. 116 </p> 117 </div> 118 <div class="sect3" lang="en" xml:lang="en"> 119 <div class="titlepage"> 120 <div> 121 <div> 122 <h4 class="title"><a id="id1644721"></a>ncache</h4> 123 </div> 124 </div> 125 </div> 126 <p> 127 The <span class="bold"><strong>ncache</strong></span> parameter is the number of 128 caches to create. 129 </p> 130 </div> 131 </div> 132 <div class="sect2" lang="en" xml:lang="en"> 133 <div class="titlepage"> 134 <div> 135 <div> 136 <h3 class="title"><a id="id1644740"></a>Errors</h3> 137 </div> 138 </div> 139 </div> 140 <p> 141 The <code class="methodname">DB->set_cachesize()</code> <span> 142 <span> 143 method may fail and return one of the following non-zero errors: 144 </span> 145 146 </span> 147 </p> 148 <div class="sect3" lang="en" xml:lang="en"> 149 <div class="titlepage"> 150 <div> 151 <div> 152 <h4 class="title"><a id="id1644696"></a>EINVAL</h4> 153 </div> 154 </div> 155 </div> 156 <p> 157 If the specified cache size was impossibly small; the method was 158 called after <a class="xref" href="dbopen.html" title="DB->open()">DB->open()</a> 159 was called; or if an invalid flag value or parameter was specified. 160 </p> 161 </div> 162 </div> 163 <div class="sect2" lang="en" xml:lang="en"> 164 <div class="titlepage"> 165 <div> 166 <div> 167 <h3 class="title"><a id="id1644779"></a>Class</h3> 168 </div> 169 </div> 170 </div> 171 <p> 172 <a class="link" href="db.html" title="Chapter��2.�� The DB Handle">DB</a> 173 </p> 174 </div> 175 <div class="sect2" lang="en" xml:lang="en"> 176 <div class="titlepage"> 177 <div> 178 <div> 179 <h3 class="title"><a id="id1644485"></a>See Also</h3> 180 </div> 181 </div> 182 </div> 183 <p> 184 <a class="xref" href="db.html#dblist" title="Database and Related Methods">Database and Related Methods</a> 185 </p> 186 </div> 187 </div> 188 <div class="navfooter"> 189 <hr /> 190 <table width="100%" summary="Navigation footer"> 191 <tr> 192 <td width="40%" align="left"><a accesskey="p" href="dbset_bt_prefix.html">Prev</a>��</td> 193 <td width="20%" align="center"> 194 <a accesskey="u" href="db.html">Up</a> 195 </td> 196 <td width="40%" align="right">��<a accesskey="n" href="dbset_create_dir.html">Next</a></td> 197 </tr> 198 <tr> 199 <td width="40%" align="left" valign="top">DB->set_bt_prefix()��</td> 200 <td width="20%" align="center"> 201 <a accesskey="h" href="index.html">Home</a> 202 </td> 203 <td width="40%" align="right" valign="top">��DB->set_create_dir()</td> 204 </tr> 205 </table> 206 </div> 207 </body> 208</html> 209