84 lines
5.9 KiB
HTML
84 lines
5.9 KiB
HTML
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<!DOCTYPE html
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<meta name="abstract" content="In addition to the performance considerations for nondistributed join queries, more performance considerations exist for queries involving distributed files." />
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<meta name="description" content="In addition to the performance considerations for nondistributed join queries, more performance considerations exist for queries involving distributed files." />
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<meta name="DC.subject" content="join, implementation, optimization, query, join implementation, join optimization, partition compatible, definition, data types, that are partition compatible" />
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<meta name="DC.Relation" scheme="URI" content="repartitioned.htm" />
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<title>Implementation and optimization of join operations with DB2 Multisystem</title>
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</head>
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<body id="joins"><a name="joins"><!-- --></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">Implementation and optimization of join operations with DB2<sup>®</sup> Multisystem</h1>
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<div><p>In addition to the performance considerations for nondistributed
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join queries, more performance considerations exist for queries involving
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distributed files.</p>
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<p>Joins can be performed only when the data is partition compatible. The
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distributed query optimizer generates a plan that makes data partition compatible,
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which might involve moving data between nodes.</p>
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<p>Data is <em>partition compatible</em> when the data in the partitioning keys
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of both files uses the same node group and hashes to the same node. For example,
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the same numeric value stored in either a large-integer field or a small-integer
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field hashes to the same value.</p>
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<p>The data types that follow are partition compatible:</p>
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<ul><li>Large integer (4-byte), small integer (2-byte), packed decimal, and zoned
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numeric.</li>
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<li>Fixed-length and varying-length SBCS character and DBCS-open, -either,
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or -only.</li>
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<li>Fixed-length and varying-length graphic.</li>
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</ul>
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<p>Date, time, timestamp, and floating-point numeric data types are not partition
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compatible because they cannot be partitioning keys.</p>
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<p>Joins involving distributed files are classified into four types: collocated,
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directed, repartitioned, and broadcast. The following sections define the
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types of joins and give examples of the different join types.</p>
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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="colocated.htm">Collocated join with DB2 Multisystem</a></strong><br />
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In a collocated join, corresponding records of files being joined exist on the same node.</li>
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<li class="ulchildlink"><strong><a href="directed.htm">Directed join with DB2 Multisystem</a></strong><br />
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In the directed join, the partitioning keys of at least one of the files are used as the join fields.</li>
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<li class="ulchildlink"><strong><a href="repartitioned.htm">Repartitioned join with DB2 Multisystem</a></strong><br />
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In a repartitioned join, the partitioning keys of the files are not used as the join fields.</li>
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<li class="ulchildlink"><strong><a href="broadcast.htm">Broadcast join with DB2 Multisystem</a></strong><br />
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In a broadcast join, all of the selected records of one file are sent or broadcast to all the nodes of the other file before the join is performed.</li>
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<li class="ulchildlink"><strong><a href="joinopt.htm">Join optimization with DB2 Multisystem</a></strong><br />
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The distributed query optimizer generates a plan to join distributed files.</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="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 class="relconcepts"><strong>Related concepts</strong><br />
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<div><a href="joinopt.htm" title="The distributed query optimizer generates a plan to join distributed files.">Join optimization 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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