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_h_ffactor()</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_h_compare.html" title="Db::set_h_compare()" /> 12 <link rel="next" href="dbset_h_hash.html" title="Db::set_h_hash()" /> 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_h_ffactor()</th> 19 </tr> 20 <tr> 21 <td width="20%" align="left"><a accesskey="p" href="dbset_h_compare.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_h_hash.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_h_ffactor"></a>Db::set_h_ffactor()</h2> 35 </div> 36 </div> 37 </div> 38 <pre class="programlisting">#include <db_cxx.h> 39 40int 41Db::set_h_ffactor(u_int32_t h_ffactor); </pre> 42 <p> 43 Set the desired density within the hash table. If no value is 44 specified, the fill factor will be selected dynamically as pages 45 are filled. 46 </p> 47 <p> 48 The density is an approximation of the number of keys allowed to 49 accumulate in any one bucket, determining when the hash table grows or 50 shrinks. If you know the average sizes of the keys and data in your 51 data set, setting the fill factor can enhance performance. A reasonable 52 rule computing fill factor is to set it to the following: 53 </p> 54 <pre class="programlisting"> (pagesize - 32) / (average_key_size + average_data_size + 8) </pre> 55 <p> 56 The <code class="methodname">Db::set_h_ffactor()</code> method configures a database, not only 57 operations performed using the specified 58 <a class="link" href="db.html" title="Chapter 2. The Db Handle">Db</a> handle. 59 </p> 60 <p> 61 The <code class="methodname">Db::set_h_ffactor()</code> method may not be called after the 62 <a class="xref" href="dbopen.html" title="Db::open()">Db::open()</a> method is called. If 63 the database already exists when <a class="xref" href="dbopen.html" title="Db::open()">Db::open()</a> 64 is called, the information specified to <code class="methodname">Db::set_h_ffactor()</code> will be ignored. 65 </p> 66 <p> 67 The <code class="methodname">Db::set_h_ffactor()</code> <span> 68 69 <span> 70 method either returns a non-zero error value or throws an 71 exception that encapsulates a non-zero error value on 72 failure, and returns 0 on success. 73 </span> 74 </span> 75 </p> 76 <div class="sect2" lang="en" xml:lang="en"> 77 <div class="titlepage"> 78 <div> 79 <div> 80 <h3 class="title"><a id="id1647041"></a>Parameters</h3> 81 </div> 82 </div> 83 </div> 84 <div class="sect3" lang="en" xml:lang="en"> 85 <div class="titlepage"> 86 <div> 87 <div> 88 <h4 class="title"><a id="id1648325"></a>h_ffactor</h4> 89 </div> 90 </div> 91 </div> 92 <p> 93 The <span class="bold"><strong>h_ffactor</strong></span> parameter is the 94 desired density within the hash table. 95 </p> 96 </div> 97 </div> 98 <div class="sect2" lang="en" xml:lang="en"> 99 <div class="titlepage"> 100 <div> 101 <div> 102 <h3 class="title"><a id="id1648542"></a>Errors</h3> 103 </div> 104 </div> 105 </div> 106 <p> 107 The <code class="methodname">Db::set_h_ffactor()</code> <span> 108 109 <span> 110 method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a> 111 exception, encapsulating one of the following non-zero errors, or return one 112 of the following non-zero errors: 113 </span> 114 </span> 115 </p> 116 <div class="sect3" lang="en" xml:lang="en"> 117 <div class="titlepage"> 118 <div> 119 <div> 120 <h4 class="title"><a id="id1648402"></a>EINVAL</h4> 121 </div> 122 </div> 123 </div> 124 <p> 125 If the method was called after <a class="xref" href="dbopen.html" title="Db::open()">Db::open()</a> 126 was called; or if an invalid flag value or parameter was specified. 127 </p> 128 </div> 129 </div> 130 <div class="sect2" lang="en" xml:lang="en"> 131 <div class="titlepage"> 132 <div> 133 <div> 134 <h3 class="title"><a id="id1648566"></a>Class</h3> 135 </div> 136 </div> 137 </div> 138 <p> 139 <a class="link" href="db.html" title="Chapter 2. The Db Handle">Db</a> 140 </p> 141 </div> 142 <div class="sect2" lang="en" xml:lang="en"> 143 <div class="titlepage"> 144 <div> 145 <div> 146 <h3 class="title"><a id="id1648493"></a>See Also</h3> 147 </div> 148 </div> 149 </div> 150 <p> 151 <a class="xref" href="db.html#dblist" title="Database and Related Methods">Database and Related Methods</a> 152 </p> 153 </div> 154 </div> 155 <div class="navfooter"> 156 <hr /> 157 <table width="100%" summary="Navigation footer"> 158 <tr> 159 <td width="40%" align="left"><a accesskey="p" href="dbset_h_compare.html">Prev</a> </td> 160 <td width="20%" align="center"> 161 <a accesskey="u" href="db.html">Up</a> 162 </td> 163 <td width="40%" align="right"> <a accesskey="n" href="dbset_h_hash.html">Next</a></td> 164 </tr> 165 <tr> 166 <td width="40%" align="left" valign="top">Db::set_h_compare() </td> 167 <td width="20%" align="center"> 168 <a accesskey="h" href="index.html">Home</a> 169 </td> 170 <td width="40%" align="right" valign="top"> Db::set_h_hash()</td> 171 </tr> 172 </table> 173 </div> 174 </body> 175</html> 176