<html>
<head>
<META http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Indexing</title>
<link rel="stylesheet" type="text/css" href="../../style.css">
</head>
<body>
<div class="CommonContent">
<div class="CommonContentArea">
<h1>Indexing</h1>
<p>db4o allows to index fields to provide maximum querying performance. To request an index to be created, you would issue the following API method call in your global <a href="configuration.html" class="wikiLink">db4o configuration method</a> before you open an ObjectContainer/ObjectServer:</p>
<p>// assuming</p>
<p><code>class Foo{<br> String bar;<br>}</code></p>
<span name="cs_wiki_filter" csw_filters="net">
<p>.NET: </p><p><code>configuration.ObjectClass(typeof(Foo)).ObjectField("bar").Indexed(true); </code></p>
</span>
<p>If the configuration is set in this way, an index on the Foo#bar field will be created (if not present already) the next time you open an ObjectContainer/ObjectServer and you use the Foo class the first time in your applcation. </p>
<p>Contrary to all other <a href="configuration.html" class="wikiLink">configuration calls</a> indexes - once created - will remain in a database even if the index configuration call is not issued before opening an ObjectContainer/ObjectServer. </p>
<p>To drop an index you would also issue a configuration call in your db4o configuration method:</p>
<p>Actually dropping the index will take place the next time the respective class is used.db4o will tell you when it creates and drops indexes, if you choose a message level of 1 or higher:</p>
<span name="cs_wiki_filter" csw_filters="net">
<p>.NET: </p><p><code>configuration.MessageLevel(1);</code></p>
</span>
<p>For creating and dropping indexes on large amounts of objects there are two possible strategies:</p>
<ol>
<li>Import all objects with indexing off, configure the index and reopen the ObjectContainer/ObjectServer.</li>
<li>Import all objects with indexing turned on and commit regularly for a fixed amount of objects (~10,000).</li></ol>
<ol>
<li>will be faster.</li>
<li>will keep memory consumption lower.</li></ol>
<p>For more information see <a href="performance_hints/enable_field_indexes.html" class="wikiLink">Enable Field Indexes</a> chapter.</p></div>
</div>
<div id="footer">
This revision (13) was last Modified 2007-05-07T16:49:45 by Tetyana.
</div>
</body>
</html>
