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</td></tr></table><table id="gradientTable"><tr><td class="nsrBottom" background="../icons/gradient.gif" /></tr></table></div><div id="mainSection"><div id="mainBody"><div id="allHistory" class="saveHistory" onsave="saveAll()" onload="loadAll()" /><span style="color: DarkGray"> </span><div class="summary">
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The Btree prefix function.
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</div><p />
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<b>Namespace:</b>
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<a href="N_BerkeleyDB.htm">BerkeleyDB</a><br />
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<b>Assembly:</b>
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<span sdata="assembly">libdb_dotnet62</span> (in libdb_dotnet62.dll) Version: 6.2.23.0<h1 class="heading"><span onclick="ExpandCollapse(syntaxToggle)" style="cursor:default;" onkeypress="ExpandCollapse_CheckKey(syntaxToggle, event)" tabindex="0"><img id="syntaxToggle" class="toggle" name="toggleSwitch" src="../icons/collapse_all.gif" />Syntax</span></h1><div id="syntaxSection" class="section" name="collapseableSection" style=""><div id="syntaxCodeBlocks" class="code"><span codeLanguage="CSharp"><table><tr><th>C#</th></tr><tr><td><pre xml:space="preserve"><span class="keyword">public</span> <a href="T_BerkeleyDB_EntryPrefixComparisonDelegate.htm">EntryPrefixComparisonDelegate</a> <span class="identifier">PrefixCompare</span></pre></td></tr></table></span><span codeLanguage="VisualBasicDeclaration"><table><tr><th>Visual Basic (Declaration)</th></tr><tr><td><pre xml:space="preserve"><span class="keyword">Public</span> <span class="identifier">PrefixCompare</span> <span class="keyword">As</span> <a href="T_BerkeleyDB_EntryPrefixComparisonDelegate.htm">EntryPrefixComparisonDelegate</a></pre></td></tr></table></span><span codeLanguage="ManagedCPlusPlus"><table><tr><th>Visual C++</th></tr><tr><td><pre xml:space="preserve"><span class="keyword">public</span>:
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<a href="T_BerkeleyDB_EntryPrefixComparisonDelegate.htm">EntryPrefixComparisonDelegate</a>^ <span class="identifier">PrefixCompare</span></pre></td></tr></table></span></div></div><h1 class="heading"><span onclick="ExpandCollapse(remarksToggle)" style="cursor:default;" onkeypress="ExpandCollapse_CheckKey(remarksToggle, event)" tabindex="0"><img id="remarksToggle" class="toggle" name="toggleSwitch" src="../icons/collapse_all.gif" />Remarks</span></h1><div id="remarksSection" class="section" name="collapseableSection" style="">
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<p>
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The prefix function is used to determine the amount by which keys
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stored on the Btree internal pages can be safely truncated without
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losing their uniqueness. See the Btree prefix comparison section of
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the Berkeley DB Reference Guide for more details about how this
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works. The usefulness of this is data-dependent, but can produce
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significantly reduced tree sizes and search times in some data sets.
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</p>
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<p>
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If no prefix function or key comparison function is specified by the
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application, a default lexical comparison function is used as the
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prefix function. If no prefix function is specified and
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<a href="F_BerkeleyDB_SecondaryBTreeDatabaseConfig_Compare.htm">Compare</a> is specified, no prefix function is
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used. It is an error to specify a prefix function without also
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specifying <a href="F_BerkeleyDB_SecondaryBTreeDatabaseConfig_Compare.htm">Compare</a>.
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</p>
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<p>
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If the database already exists, the prefix function must be the
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same as that historically used to create the database or corruption
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can occur.
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</p>
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</div><h1 class="heading"><span onclick="ExpandCollapse(seeAlsoToggle)" style="cursor:default;" onkeypress="ExpandCollapse_CheckKey(seeAlsoToggle, event)" tabindex="0"><img id="seeAlsoToggle" class="toggle" name="toggleSwitch" src="../icons/collapse_all.gif" />See Also</span></h1><div id="seeAlsoSection" class="section" name="collapseableSection" style=""><div class="seeAlsoStyle"><a href="T_BerkeleyDB_SecondaryBTreeDatabaseConfig.htm">SecondaryBTreeDatabaseConfig Class</a></div><div class="seeAlsoStyle"><a href="N_BerkeleyDB.htm">BerkeleyDB Namespace</a></div></div></div><div id="footer"><div class="footerLine"><img width="100%" height="3px" src="../icons/footer.gif" title="Footer image" /></div><A NAME="feedback"></A><span id="fb" class="feedbackcss"> </span>
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