60 lines
4.0 KiB
HTML
60 lines
4.0 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.Title" content="Optimization overview with DB2 Multisystem" />
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<meta name="abstract" content="Distributed queries are optimized at the distributed level and the local level." />
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<meta name="description" content="Distributed queries are optimized at the distributed level and the local level." />
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<meta name="DC.subject" content="optimization, overview, of distributed queries, query, optimization overview, distributed query, definition, temporary result file, temporary result file, distributed query" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<title>Optimization overview with DB2 Multisystem</title>
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</head>
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<body id="optov"><a name="optov"><!-- --></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">Optimization overview with DB2<sup>®</sup> Multisystem</h1>
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<div><p>Distributed queries are optimized at the distributed level and
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the local level.</p>
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<ul><li>Optimization at the distributed level focuses on dividing
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the query into the most efficient steps and determining which nodes process
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those steps. The distributed optimizer is distinctive to distributed queries.
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The distributed optimizer is discussed in this topic.</li>
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<li>Optimization at the local (step) level is the same optimization that occurs
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in a nondistributed environment; it is the optimizer with which you are probably
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familiar. Local-level optimization is discussed minimally in this topic.</li>
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</ul>
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<p>A basic assumption of distributed optimization is that the number of records
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stored at each data node is approximately equal and that all of the systems
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of the distributed query are of similar configurations. The decisions made
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by the distributed optimizer are based on the system and the data statistics
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of the coordinator node system.</p>
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<p>If a distributed query requires more than one step, a temporary result
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file is used. A <em>temporary result file</em> is a system-created temporary
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file (stored in library QRECOVERY) that is used to contain the results of
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a particular query step. The contents of the temporary result file are used
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as input to the next query step.</p>
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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="qqp.htm" title="This topic provides you with some guidelines for designing queries so that they use query resources more efficiently when you run queries that use distributed files.">Query design for performance with DB2 Multisystem</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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