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_ENV->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="memp.html" title="Chapter��8.�� The DB_MPOOLFILE Handle" /> 11 <link rel="prev" href="envset_cache_max.html" title="DB_ENV->set_cache_max()" /> 12 <link rel="next" href="mempset_mp_max_openfd.html" title="DB_ENV->set_mp_max_openfd()" /> 13 </head> 14 <body> 15 <div class="navheader"> 16 <table width="100%" summary="Navigation header"> 17 <tr> 18 <th colspan="3" align="center">DB_ENV->set_cachesize()</th> 19 </tr> 20 <tr> 21 <td width="20%" align="left"><a accesskey="p" href="envset_cache_max.html">Prev</a>��</td> 22 <th width="60%" align="center">Chapter��8.�� 23 The DB_MPOOLFILE Handle 24 </th> 25 <td width="20%" align="right">��<a accesskey="n" href="mempset_mp_max_openfd.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="envset_cachesize"></a>DB_ENV->set_cachesize()</h2> 35 </div> 36 </div> 37 </div> 38 <pre class="programlisting">#include <db.h> 39 40int 41DB_ENV->set_cachesize(DB_ENV *dbenv, 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 cache 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 The cache may be resized by calling <code class="methodname">DB_ENV->set_cachesize()</code> 71 after the environment is open. The supplied size will be rounded to the nearest multiple 72 of the region size and may not be larger than the maximum size configured with 73 <a class="xref" href="envset_cache_max.html" title="DB_ENV->set_cache_max()">DB_ENV->set_cache_max()</a>. The 74 <span class="bold"><strong>ncache</strong></span> parameter is ignored when resizing the cache. 75 76 </p> 77 <p> 78 The database environment's initial cache size may also be configured 79 using the environment's <a href="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class="olink">DB_CONFIG</a> file. The 80 syntax of the entry in that file is a single line with the string 81 "set_cachesize", one or more whitespace characters, and the initial 82 cache size specified in three parts: the gigabytes of cache, the 83 additional bytes of cache, and the number of caches, also separated by 84 whitespace characters. For example, "set_cachesize 2 524288000 3" 85 would create a 2.5GB logical cache, split between three physical 86 caches. Because the <a href="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class="olink">DB_CONFIG</a> file is 87 read when the database environment is opened, it will silently 88 overrule configuration done before that time. 89 </p> 90 <p> 91 The <code class="methodname">DB_ENV->set_cachesize()</code> method configures a database environment, 92 not only operations performed using the specified <a class="link" href="env.html" title="Chapter��5.�� The DB_ENV Handle">DB_ENV</a> handle. 93 </p> 94 <p> 95 The <code class="methodname">DB_ENV->set_cachesize()</code> method may be called at any time during 96 the life of the application. 97 </p> 98 <p> 99 The <code class="methodname">DB_ENV->set_cachesize()</code> <span> 100 <span> 101 method returns a non-zero error value on failure and 0 on success. 102 </span> 103 104 </span> 105 </p> 106 <div class="sect2" lang="en" xml:lang="en"> 107 <div class="titlepage"> 108 <div> 109 <div> 110 <h3 class="title"><a id="id1688516"></a>Parameters</h3> 111 </div> 112 </div> 113 </div> 114 <div class="sect3" lang="en" xml:lang="en"> 115 <div class="titlepage"> 116 <div> 117 <div> 118 <h4 class="title"><a id="id1688522"></a>bytes</h4> 119 </div> 120 </div> 121 </div> 122 <p> 123 The size of the cache is set to <span class="bold"><strong>gbytes</strong></span> gigabytes plus <span class="bold"><strong>bytes</strong></span>. 124 </p> 125 </div> 126 <div class="sect3" lang="en" xml:lang="en"> 127 <div class="titlepage"> 128 <div> 129 <div> 130 <h4 class="title"><a id="id1688666"></a>gbytes</h4> 131 </div> 132 </div> 133 </div> 134 <p> 135 The size of the cache is set to <span class="bold"><strong>gbytes</strong></span> gigabytes plus <span class="bold"><strong>bytes</strong></span>. 136 </p> 137 </div> 138 <div class="sect3" lang="en" xml:lang="en"> 139 <div class="titlepage"> 140 <div> 141 <div> 142 <h4 class="title"><a id="id1688254"></a>ncache</h4> 143 </div> 144 </div> 145 </div> 146 <p> 147 The <span class="bold"><strong>ncache</strong></span> parameter is the number of 148 caches to create. 149 </p> 150 </div> 151 </div> 152 <div class="sect2" lang="en" xml:lang="en"> 153 <div class="titlepage"> 154 <div> 155 <div> 156 <h3 class="title"><a id="id1688706"></a>Errors</h3> 157 </div> 158 </div> 159 </div> 160 <p> 161 The <code class="methodname">DB_ENV->set_cachesize()</code> <span> 162 <span> 163 method may fail and return one of the following non-zero errors: 164 </span> 165 166 </span> 167 </p> 168 <div class="sect3" lang="en" xml:lang="en"> 169 <div class="titlepage"> 170 <div> 171 <div> 172 <h4 class="title"><a id="id1688657"></a>EINVAL</h4> 173 </div> 174 </div> 175 </div> 176 <p> 177 If the specified cache size was impossibly small; or if an invalid 178 flag value or parameter was specified. 179 </p> 180 </div> 181 </div> 182 <div class="sect2" lang="en" xml:lang="en"> 183 <div class="titlepage"> 184 <div> 185 <div> 186 <h3 class="title"><a id="id1688658"></a>Class</h3> 187 </div> 188 </div> 189 </div> 190 <p> 191 <a class="link" href="env.html" title="Chapter��5.�� The DB_ENV Handle">DB_ENV</a> 192 </p> 193 </div> 194 <div class="sect2" lang="en" xml:lang="en"> 195 <div class="titlepage"> 196 <div> 197 <div> 198 <h3 class="title"><a id="id1688530"></a>See Also</h3> 199 </div> 200 </div> 201 </div> 202 <p> 203 <a class="xref" href="env.html#envlist" title="Database Environments and Related Methods">Database Environments and Related Methods</a> 204 </p> 205 </div> 206 </div> 207 <div class="navfooter"> 208 <hr /> 209 <table width="100%" summary="Navigation footer"> 210 <tr> 211 <td width="40%" align="left"><a accesskey="p" href="envset_cache_max.html">Prev</a>��</td> 212 <td width="20%" align="center"> 213 <a accesskey="u" href="memp.html">Up</a> 214 </td> 215 <td width="40%" align="right">��<a accesskey="n" href="mempset_mp_max_openfd.html">Next</a></td> 216 </tr> 217 <tr> 218 <td width="40%" align="left" valign="top">DB_ENV->set_cache_max()��</td> 219 <td width="20%" align="center"> 220 <a accesskey="h" href="index.html">Home</a> 221 </td> 222 <td width="40%" align="right" valign="top">��DB_ENV->set_mp_max_openfd()</td> 223 </tr> 224 </table> 225 </div> 226 </body> 227</html> 228