90 lines
6.4 KiB
HTML
90 lines
6.4 KiB
HTML
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<?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="reference" />
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<meta name="DC.Title" content="Query optimizer index advisor" />
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<meta name="abstract" content="The query optimizer analyzes the row selection in the query and determines, based on default values, if creation of a permanent index improves performance. If the optimizer determines that a permanent index might be beneficial, it returns the key columns necessary to create the suggested index." />
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<meta name="description" content="The query optimizer analyzes the row selection in the query and determines, based on default values, if creation of a permanent index improves performance. If the optimizer determines that a permanent index might be beneficial, it returns the key columns necessary to create the suggested index." />
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<meta name="DC.subject" content="query optimizer index advisor, optimizer, query index advisor, index advisor, query optimizer, advisor, query optimizer index" />
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<meta name="keywords" content="query optimizer index advisor, optimizer, query index advisor, index advisor, query optimizer, advisor, query optimizer index" />
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<meta name="DC.Relation" scheme="URI" content="queryopt.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzajqshowindexes.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzajqadvise3020.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzajqovrve.htm" />
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<meta name="DC.Relation" scheme="URI" content="t3020.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Identifier" content="idxadvisor" />
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Query optimizer index advisor</title>
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</head>
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<body id="idxadvisor"><a name="idxadvisor"><!-- --></a>
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<img src="./delta.gif" alt="Start of change" /><!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Query optimizer index advisor</h1>
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<div><p>The query optimizer analyzes the row selection in the query and
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determines, based on default values, if creation of a permanent index improves
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performance. If the optimizer determines that a permanent index might be beneficial,
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it returns the key columns necessary to create the suggested index.</p>
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<div class="section"><p>The optimizer is able to perform radix index probe over any combination
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of the primary key columns, plus one additional secondary key column. Therefore
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it is important that the first secondary key column be the most selective
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secondary key column. The optimizer will use radix index scan with any of
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the remaining secondary key columns. While radix index scan is not as fast
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as radix index probe it can still reduce the number of keys selected. Hence,
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secondary key columns that are fairly selective should be included.</p>
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</div>
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<div class="section"><p>It is up to the user to determine the true selectivity of any
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secondary key columns and to determine whether those key columns should be
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included when creating the index. When building the index the primary key
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columns should be the left-most key columns followed by any of the secondary
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key columns the user chooses and they should be prioritized by selectivity.</p>
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<div class="note"><span class="notetitle">Note:</span> After
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creating the suggested index and executing the query again, it is possible
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that the query optimizer will choose not to use the suggested index. The CQE
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optimizer when suggesting indexes only considers the selection criteria and
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does not include join, ordering, and grouping criteria. The SQE optimizer
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includes selection, join, ordering, and grouping criteria when suggesting
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indexes.</div>
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</div>
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<div class="section"><p>You can access index advisor information in many different ways.
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These include:</p>
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<ul><li>The index advisor interface in iSeries™ Navigator</li>
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<li>SQL performance monitor Show statements</li>
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<li>Visual Explain interface</li>
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<li>Querying the Database monitor view 3020 - Index advised.</li>
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</ul>
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</div>
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</div>
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<div>
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<ul class="ullinks">
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<li class="ulchildlink"><img src="./delta.gif" alt="Start of change" /><strong><a href="rzajqshowindexes.htm">Display index advisor information</a></strong><img src="./deltaend.gif" alt="End of change" /><br />
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You can display index advisor information from the optimizer using iSeries Navigator.</li>
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<li class="ulchildlink"><strong><a href="rzajqadvise3020.htm">Querying database monitor view 3020 - Index advised</a></strong><br />
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The index advisor information can be found in the Database Monitor view 3020 - Index advised (SQE).</li>
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</ul>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="queryopt.htm" title="Query optimization is an iterative process. You can gather performance information about your queries and control the processing of your queries.">Optimizing query performance using query optimization tools</a></div>
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</div>
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<div class="relref"><strong>Related reference</strong><br />
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<div><a href="rzajqovrve.htm" title="You can use Visual Explain to view many types of information.">Overview of information available from Visual Explain</a></div>
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<div><a href="t3020.htm">Database monitor view 3020 - Index advised (SQE)</a></div>
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<div><a href="rzajqmonstatements.htm" title="You can view SQL statements that are included in a detailed monitor.">Viewing statements in a monitor</a></div>
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</div>
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</div>
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<img src="./deltaend.gif" alt="End of change" /></body>
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</html>
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