64 lines
3.9 KiB
HTML
64 lines
3.9 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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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name="security" content="public" />
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<meta name="Robots" content="index,follow" />
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<meta http-equiv="PICS-Label" content='(PICS-1.1 "http://www.icra.org/ratingsv02.html" l gen true r (cz 1 lz 1 nz 1 oz 1 vz 1) "http://www.rsac.org/ratingsv01.html" l gen true r (n 0 s 0 v 0 l 0) "http://www.classify.org/safesurf/" l gen true r (SS~~000 1))' />
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<meta name="DC.Type" content="reference" />
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<meta name="DC.Title" content="Optimizer" />
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<meta name="abstract" content="Optimizer is an important module of the i5/OS Query component because it makes the key decisions for good database performance. Its main objective is to find the most efficient access path to the data." />
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<meta name="description" content="Optimizer is an important module of the i5/OS Query component because it makes the key decisions for good database performance. Its main objective is to find the most efficient access path to the data." />
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<meta name="DC.Relation" scheme="URI" content="rzaiksqlperf.htm" />
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<meta name="DC.Relation" scheme="URI" content="costest.htm" />
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<meta name="DC.Relation" scheme="URI" content="optdecrules.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1999, 2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1999, 2006" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Identifier" content="optimizer" />
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<meta name="DC.Language" content="en-us" />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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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>Optimizer</title>
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</head>
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<body id="optimizer"><a name="optimizer"><!-- --></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">Optimizer</h1>
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<div><p>Optimizer is an important module of the <span class="keyword">i5/OS™</span> Query
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component because it makes the key decisions for good database performance.
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Its main objective is to find the most efficient access path to the data.</p>
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<div class="section"><p>Query optimization is a trade-off between the time spent to select
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a query implementation and the time spent to run it. Query optimization must
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handle the following distinct user needs: </p>
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<ul><li>Quick interactive response</li>
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<li>Efficient use of total-machine resources</li>
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</ul>
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</div>
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<div class="section"><p>In deciding how to access data, Optimizer does the following:
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</p>
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<ul><li>Determines possible implementations</li>
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<li>Picks the optimal implementation for the <span class="keyword">i5/OS</span> Query
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component to execute</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"><strong><a href="costest.htm">Cost estimation</a></strong><br />
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At runtime, the Optimizer chooses an optimal access method for the query by calculating an implementation cost based on the current state of the database.</li>
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<li class="ulchildlink"><strong><a href="optdecrules.htm">Optimizer decision-making rules</a></strong><br />
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In performing its function, Optimizer uses a general set of guidelines to choose the best method for accessing data.</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="rzaiksqlperf.htm" title="Good application design includes the efficient use of machine resources. To run in a manner that is acceptable to the end user, an application program must be efficient in operation, and must run with adequate response time.">SQL performance</a></div>
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</div>
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</div>
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</body>
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</html>
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