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<title>PartialComparator (Oracle - Berkeley DB Java Edition API)</title>
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<div class="aboutLanguage"><b>Berkeley DB Java Edition</b><br><font size=\"-1\"> version 7.5.11</font>
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<div class="subTitle">com.sleepycat.je</div>
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<h2 title="Interface PartialComparator" class="title">Interface PartialComparator</h2>
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<pre>public interface <span class="typeNameLabel">PartialComparator</span></pre>
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<div class="block">A tag interface used to mark a B-tree or duplicate comparator class as a
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partial comparator.
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Comparators are configured using
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<a href="../../../com/sleepycat/je/DatabaseConfig.html#setBtreeComparator-java.util.Comparator-"><code>DatabaseConfig.setBtreeComparator(java.util.Comparator)</code></a> or
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<a href="../../../com/sleepycat/je/DatabaseConfig.html#setBtreeComparator-java.lang.Class-"><code>DatabaseConfig.setBtreeComparator(Class)</code></a>, and
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<a href="../../../com/sleepycat/je/DatabaseConfig.html#setDuplicateComparator-java.util.Comparator-"><code>DatabaseConfig.setDuplicateComparator(java.util.Comparator)</code></a> or
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<a href="../../../com/sleepycat/je/DatabaseConfig.html#setDuplicateComparator-java.lang.Class-"><code>DatabaseConfig.setDuplicateComparator(Class)</code></a>.
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<p>
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As described in the javadoc for these methods, a partial comparator is a
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comparator that allows for the keys of a database to be updated, but only
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if the updates are not significant with respect to uniqueness and ordering.
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Also described is the fact that comparators must be used with great caution,
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since a badly behaved comparator can cause B-tree corruption.
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<p>
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Even greater caution is needed when using partial comparators, for several
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reasons. Partial comparators are normally used for performance reasons in
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certain situations, but the performance trade-offs are very subtle and
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difficult to understand. In addition, as of JE 6, this tag interface must
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be added to all partial comparator classes so that JE can correctly perform
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transaction aborts, while maintaining the last committed key or duplicate
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data values properly. In addition, for a database with duplicates
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configured, a partial comparator (implementing this tag interface) will
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disable optimizations in JE 6 that drastically reduce cleaner costs.
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<p>
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For these reasons, we do not recommend using partial comparators, although
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they are supported in order to avoid breaking applications that used them
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prior to JE 6. Whenever possible, please avoid using partial comparators.</div>
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<div class="aboutLanguage"><b>Berkeley DB Java Edition</b><br><font size=\"-1\"> version 7.5.11</font>
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