91 lines
3.8 KiB
HTML
91 lines
3.8 KiB
HTML
<!--$Id: db_set_h_ffactor.html 63573 2008-05-23 21:43:21Z trent.nelson $-->
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<!--Copyright (c) 1997,2008 Oracle. All rights reserved.-->
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<!--See the file LICENSE for redistribution information.-->
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<html>
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<head>
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<title>Berkeley DB: Db::set_h_ffactor</title>
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<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
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<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++">
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</head>
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<body bgcolor=white>
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<table width="100%"><tr valign=top>
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<td>
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<b>Db::set_h_ffactor</b>
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</td>
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<td align=right>
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<a href="../api_cxx/api_core.html"><img src="../images/api.gif" alt="API"></a>
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<a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a></td>
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</tr></table>
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<hr size=1 noshade>
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<tt>
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<b><pre>
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#include <db_cxx.h>
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<p>
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int
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Db::set_h_ffactor(u_int32_t h_ffactor);
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<p>
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int Db::get_h_ffactor(u_int32_t *h_ffactorp);
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</pre></b>
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<hr size=1 noshade>
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<b>Description: Db::set_h_ffactor</b>
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<p>Set the desired density within the hash table. If no value is
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specified, the fill factor will be selected dynamically as pages are
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filled.</p>
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<p>The Db::set_h_ffactor method configures a database, not only operations performed
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using the specified <a href="../api_cxx/db_class.html">Db</a> handle.</p>
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<p>The Db::set_h_ffactor method may not be called after the <a href="../api_cxx/db_open.html">Db::open</a> method is called.
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If the database already exists when
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<a href="../api_cxx/db_open.html">Db::open</a> is called, the information specified to Db::set_h_ffactor will
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be ignored.
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</p>
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<p>The Db::set_h_ffactor method
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either returns a non-zero error value
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or throws an exception that encapsulates a non-zero error value on
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failure, and returns 0 on success.
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</p>
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<b>Parameters</b> <br>
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<b>h_ffactor</b><ul compact><li>The <b>h_ffactor</b> parameter is the desired density within the hash table.</ul>
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<p>The density is an approximation of the number of keys allowed to
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accumulate in any one bucket, determining when the hash table grows or
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shrinks. If you know the average sizes of the keys and data in your
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data set, setting the fill factor can enhance performance. A reasonable
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rule computing fill factor is to set it to the following:</p>
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<blockquote><pre>(pagesize - 32) / (average_key_size + average_data_size + 8)</pre></blockquote>
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<br>
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<br><b>Errors</b>
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<p>The Db::set_h_ffactor method
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may fail and throw
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<a href="../api_cxx/except_class.html">DbException</a>,
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encapsulating one of the following non-zero errors, or return one of
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the following non-zero errors:</p>
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<br>
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<b>EINVAL</b><ul compact><li>If the method was called after <a href="../api_cxx/db_open.html">Db::open</a> was called; or if an
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invalid flag value or parameter was specified.</ul>
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<br>
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<hr size=1 noshade>
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<b>Description: Db::get_h_ffactor</b>
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<p>The Db::get_h_ffactor method returns the hash table density.</p>
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<p>The Db::get_h_ffactor method may be called at any time during the life of the
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application.</p>
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<p>The Db::get_h_ffactor method
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either returns a non-zero error value
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or throws an exception that encapsulates a non-zero error value on
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failure, and returns 0 on success.
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</p>
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<b>Parameters</b> <br>
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<b>h_ffactorp</b><ul compact><li>The Db::get_h_ffactor method returns the
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hash table density in <b>h_ffactorp</b>.</ul>
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<br>
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<hr size=1 noshade>
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<br><b>Class</b>
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<a href="../api_cxx/db_class.html">Db</a>
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<br><b>See Also</b>
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<a href="../api_cxx/db_list.html">Databases and Related Methods</a>
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</tt>
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<table width="100%"><tr><td><br></td><td align=right>
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<a href="../api_cxx/api_core.html"><img src="../images/api.gif" alt="API"></a><a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a>
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</td></tr></table>
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<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font>
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</body>
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</html>
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