<?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_h_ffactor()</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_h_compare.html" title="Db::set_h_compare()" /> <link rel="next" href="dbset_h_hash.html" title="Db::set_h_hash()" /> </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_h_ffactor()</th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="dbset_h_compare.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_h_hash.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_h_ffactor"></a>Db::set_h_ffactor()</h2> </div> </div> </div> <pre class="programlisting">#include <db_cxx.h> int Db::set_h_ffactor(u_int32_t h_ffactor); </pre> <p> Set the desired density within the hash table. If no value is specified, the fill factor will be selected dynamically as pages are filled. </p> <p> The density is an approximation of the number of keys allowed to accumulate in any one bucket, determining when the hash table grows or shrinks. If you know the average sizes of the keys and data in your data set, setting the fill factor can enhance performance. A reasonable rule computing fill factor is to set it to the following: </p> <pre class="programlisting"> (pagesize - 32) / (average_key_size + average_data_size + 8) </pre> <p> The <code class="methodname">Db::set_h_ffactor()</code> method configures a database, not only operations performed using the specified <a class="link" href="db.html" title="Chapter 2. The Db Handle">Db</a> handle. </p> <p> The <code class="methodname">Db::set_h_ffactor()</code> method may not be called after the <a class="xref" href="dbopen.html" title="Db::open()">Db::open()</a> method is called. If the database already exists when <a class="xref" href="dbopen.html" title="Db::open()">Db::open()</a> is called, the information specified to <code class="methodname">Db::set_h_ffactor()</code> will be ignored. </p> <p> The <code class="methodname">Db::set_h_ffactor()</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="idp5578640"></a>Parameters</h3> </div> </div> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp3772776"></a>h_ffactor</h4> </div> </div> </div> <p> The <span class="bold"><strong>h_ffactor</strong></span> parameter is the desired density within the hash table. </p> </div> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="idp2762912"></a>Errors</h3> </div> </div> </div> <p> The <code class="methodname">Db::set_h_ffactor()</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="idp5623488"></a>EINVAL</h4> </div> </div> </div> <p> If 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="idp5624816"></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="idp5610224"></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_h_compare.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_h_hash.html">Next</a></td> </tr> <tr> <td width="40%" align="left" valign="top">Db::set_h_compare() </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> Db::set_h_hash()</td> </tr> </table> </div> </body> </html>