67 lines
4.1 KiB
HTML
67 lines
4.1 KiB
HTML
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<meta name="DC.Title" content="Summary of performance considerations" />
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<meta name="abstract" content="There are performance factors you should consider when developing queries that use distributed files." />
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<title>Summary of performance considerations</title>
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<body id="summary"><a name="summary"><!-- --></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">Summary of performance considerations</h1>
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<div><p>There are performance factors you should consider when developing
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queries that use distributed files.</p>
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<ol><li class="stepexpand"><span>For the OPNQRYF command and the query API (QQQQRY), specifying
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ALWCPYDTA(*OPTIMIZE) allows each node to choose an index or a sort to satisfy
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the ordering specified.</span></li>
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<li class="stepexpand"><span>For the OPNQRYF command and the query API (QQQQRY), specifying
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ALWCPYDTA(*YES) or ALWCPYDTA(*NO) enforces that each node use an index that
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exactly matches the specified ordering fields. This is more restrictive than
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the way the optimizer processes ordering for nondistributed files.</span></li>
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<li class="stepexpand"><span>Adding an ORDER BY clause to a DISTINCT select can return records
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faster by not requiring a final sort on the requesting system.</span></li>
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<li class="stepexpand"><span>Including all of the fields of the partitioning key in the grouping
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fields generally results in one-step grouping, which performs better than
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two-step grouping.</span></li>
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<li class="stepexpand"><span>Including all of the fields of the partitioning key in the join
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criteria generally results in a collocated distributed join.</span></li>
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<li class="stepexpand"><span>Including all of the fields of the partitioning key in isolatable,
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equal record selection generally results in the query being processed on only
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one node.</span></li>
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<li class="stepexpand"><span>Including any of the following scalar functions in isolatable,
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equal record selection generally results in the query being processed on only
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one node:</span> <ul><li>NODENAME</li>
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<li>NODENUMBER</li>
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<li>PARTITION</li>
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</ul>
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</li>
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</ol>
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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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