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<h1>Defragmentation Configuration</h1><div id="TOC"><div id="TOCinner"><span class="TOCtitle">Contents</span><div class="TOCcontents"><ul><li><a href ="#Original File">Original File</a></li><li><a href ="#Backup File">Backup File</a></li><li><a href ="#Mapping">Mapping</a></li><li><a href ="#Class Filter">Class Filter</a></li><li><a href ="#Database Configuration">Database Configuration</a></li><li><a href ="#Commit Frequency">Commit Frequency</a></li><li><a href ="#Upgrading">Upgrading</a></li></ul></li></ul></div></div></div>
<p>DefragmentConfig class allows you fine-tune the
defragmentation process. This topic discusses different settings available
through DefragmentConfig.</p>
<a name="Original File"></a><h2>Original File</h2>
<p>The path to the file to be defragmented. Can be specified in
the constructor:</p>
<p> <code>configuration
= new DefragmentConfig(origPath)</code></p>
<a name="Backup File"></a><h2>Backup File</h2>
<p><code>configuration = new DefragmentConfig(origPath, backupPath)</code></p>
<p>The path to the
backup of the original file. If this file exists before the defragmentation, an
IOException will be thrown and no action taken.</p>
<p>If you want the
backup file to be deleted automatically before the defragment run, specify:</p>
<span name="cs_wiki_filter" csw_filters="net">
<p>.NET:</p>
<p><code>configuration.ForceBackupDelete(true)</code></p>
</span>
<a name="Mapping"></a><h2>Mapping</h2>
<p>You can also specify the desired Mapping to be used
internally:</p>
<p><code>configuration = new DefragmentConfig(origPath, backupPath, mapping)</code></p>
<p><code>mapping</code>
is an object of a class implementing ContextIDMapping interface. Mapping is
used to keep track of objects moved during defragmentation. Db4o provides 2
mapping classes.</p>
<p><b>TreeIDMapping </b>- default in-memory mapping. Will increase the
memory usage, but is a faster alternative. Set up <a href="http://developer.db4o.com/Resources/view.aspx/Reference/Implementation_Strategies/Maintenance/Defragment/Defragmentation_Configuration#Commit Frequency">objectCommitFrequency</a> to
control memory usage.</p>
<p><b>BTreeIDMapping</b> - mapping is done in a separate file using
B-tree method. Reduces the memory usage, but is a much slower option.</p>
<a name="Class Filter"></a><h2>Class Filter</h2>
<p>Defragmentation
process uses <code>StoredClassFilter accept</code> method to define which
classes should be left in a database after the defragmentation. By default, all
classes are left. However, you can use AvailableClassFilter to get rid of the
deleted classes instances:</p>
<span name="cs_wiki_filter" csw_filters="net">
<p>.NET:</p>
<p><code>configuration.StoredClassFilter(new
AvailableClassFilter())</code></p>
</span>
<p>In this case only the classes known to the classloader will
be left in the database, the rest will be deleted.</p>
<a name="Database Configuration"></a><h2>Database Configuration</h2>
<p>For db4o configurations that influence low-level file layout
details, it is important to provide the defragmentation process with the copy
of db4o configuration:</p>
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<p>.NET:</p>
<p><code>configuration.Db4oConfig(db4oConfiguration)</code></p>
</span>
<p>For more information about db4o configuration see
<a href="../../../tuning/configuration.html" class="wikiLink">Configuration</a>.</p>
<a name="Commit Frequency"></a><h2>Commit Frequency</h2>
<p>Commit frequency sets the number of processed objects that
should trigger an immediate commit of the target file. By default, frequency =
0 and commit never happens.</p>
<span name="cs_wiki_filter" csw_filters="net">
<p>.NET:</p>
<p><code>configuration.ObjectCommitFrequency(frequency)</code></p>
</span>
<p>This method can be used to reduce memory usage during
defragmentation.</p>
<a name="Upgrading"></a><h2>Upgrading</h2>
<p>You can upgrade your database file together with the
defragmentation:</p>
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<p>.NET:</p>
<p><code>configuration.pgradeFile(tempFile)</code></p>
</span>
<p>This method can be used to reduce memory usage during
defragmentation, however it will make it slower.</p>
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This revision (8) was last Modified 2007-11-21T13:19:14 by Tetyana.
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