139 lines
5.5 KiB
HTML
139 lines
5.5 KiB
HTML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html lang="en-us" xml:lang="en-us">
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="EVI maintenance" />
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<meta name="abstract" content="There are unique challenges to maintaining EVIs. The following table shows a progression of how EVIs are maintained and the conditions under which EVIs are most effective and where EVIs are least effective based on the EVI maintenance characteristics." />
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<meta name="description" content="There are unique challenges to maintaining EVIs. The following table shows a progression of how EVIs are maintained and the conditions under which EVIs are most effective and where EVIs are least effective based on the EVI maintenance characteristics." />
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<meta name="keywords" content="index, encoded vector index maintenance, encoded vector index, maintenance" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<title>EVI maintenance</title>
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</head>
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<body id="evimaintenance"><a name="evimaintenance"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">EVI maintenance</h1>
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<div><p>There are unique challenges to maintaining EVIs. The following
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table shows a progression of how EVIs are maintained and the conditions under
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which EVIs are most effective and where EVIs are least effective based on
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the EVI maintenance characteristics.</p>
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<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" frame="border" border="1" rules="all"><caption>Table 1. EVI Maintenance Considerations</caption><thead align="left"><tr valign="bottom"><th valign="bottom" id="d0e30"> </th>
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<th valign="bottom" id="d0e31">Condition</th>
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<th valign="bottom" id="d0e33">Characteristics</th>
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</tr>
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</thead>
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<tbody><tr><td rowspan="4" valign="top" headers="d0e30 "><p></p>
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Most Effective <p><br />
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Least Effective</td>
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<td valign="top" headers="d0e31 ">When inserting an existing distinct key value</td>
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<td valign="top" headers="d0e33 "><ul><li>Minimum overhead</li>
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<li>Symbol table key value looked up and statistics updated</li>
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<li>Vector element added for new row, with existing byte code</li>
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</ul>
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</td>
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</tr>
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<tr><td valign="top" headers="d0e31 ">When inserting a <em>new</em> distinct key value - in
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order, within byte code range</td>
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<td valign="top" headers="d0e33 "><ul><li>Minimum overhead</li>
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<li>Symbol table key value added, byte code assigned, statistics assigned</li>
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<li>Vector element added for new row, with new byte code</li>
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</ul>
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</td>
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</tr>
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<tr><td valign="top" headers="d0e31 ">When inserting a new distinct key value - out of order,
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within byte code range</td>
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<td valign="top" headers="d0e33 "><ul><li>Minimum overhead if contained within overflow area threshold</li>
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<li>Symbol table key value added to overflow area, byte code assigned, statistics
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assigned</li>
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<li>Vector element added for new row, with new byte code</li>
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<li>Considerable overhead if overflow area threshold reached</li>
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<li>Access path validated - not available</li>
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<li>EVI refreshed, overflow area keys incorporated, new byte codes assigned
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(symbol table and vector elements updated)</li>
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</ul>
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</td>
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</tr>
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<tr><td valign="top" headers="d0e31 ">When inserting a new distinct key value - out of byte
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code range</td>
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<td valign="top" headers="d0e33 "><ul><li>Considerable overhead</li>
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<li>Access plan invalidated - not available</li>
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<li>EVI refreshed, next byte code size used, new byte codes assigned (symbol
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table and vector elements updated</li>
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</ul>
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</td>
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</tr>
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</tbody>
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</table>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="whatareevi.htm" title="An encoded vector index (EVI) is an index object that is used by the query optimizer and database engine to provide fast data access in decision support and query reporting environments.">Encoded vector indexes</a></div>
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</div>
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