80 lines
6.7 KiB
HTML
80 lines
6.7 KiB
HTML
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<title>How node groups work with DB2 Multisystem</title>
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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">How node groups work with DB2 Multisystem</h1>
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<div><p>A <em>node group</em> is a system object (*NODGRP), which is stored
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on the system on which it was created.</p>
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<p>A node group is not a distributed object. The *NODGRP system
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object contains all the information about the systems in the group as well
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as information about how the data in the data files should be partitioned
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(distributed). The default partitioning is for each system (node) to receive
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an equal share of the data.</p>
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<p>The partitioning is handled using a hash algorithm. When a node group
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is created, partition numbers ranging from 0 to 1023 are associated with the
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node group. With the default partitioning, an equal number of partitions are
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assigned to each of the nodes in the node group. When data is added to the
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file, the data in the partitioning key is hashed, which results in a partition
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number. The entire record of data is not hashed-only the data in the partitioning
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key is hashed through the hash algorithm. The node that is associated with
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the resulting partition number is where the record of data physically resides.
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Therefore, with the default partitioning, each node stores an equal share
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of the data, provided that there are enough records of data and a wide range
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of values.</p>
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<p>If you do not want each node to receive an equal share of the data or if
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you want to control which systems have specific pieces of data, you can change
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how the data is partitioned, either by specifying a custom partitioning scheme
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on the Create Node Group (CRTNODGRP) command using the partition file (PTNFILE)
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parameter, or by changing the partitioning scheme later using the Change Node
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Group Attributes (CHGNODGRPA) command. Using the PTNFILE parameter, you can
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set the node number for each of the partitions within the node group; in other
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words, the PTNFILE parameter allows you to tailor how you want data to be
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partitioned on the systems in the node group. (The PTNFILE parameter is used
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in an example in Creating node groups using the CRTNODGRP command with DB2<sup>®</sup> Multisystem.)
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For more information about partitioning, see Partitioning with DB2 Multisystem.</p>
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<p>Because a node group is a system object, it can be saved and restored using
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the Save Object (SAVOBJ) command and the Restore Object (RSTOBJ) command.
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You can restore a node group object either to the system on which it was created
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or to any of the systems in the node group. If the node group object is restored
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to a system that is not in the node group, the object is unusable.</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="rzaf3c2-gen4.htm" title="To enable database files to be visible across a set of iSeries servers, you must first define the group of systems (node group) that you want the files on.">Introduction of node groups 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="crtngc.htm" title="This section uses two CL command examples to show how to create a node group by using the Create Node Group (CRTNODGRP) command.">Create Node Group (CRTNODGRP) command</a></div>
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<div><a href="ption.htm" title="Partitioning is the process of distributing a file across the nodes in a node group.">Partitioning with DB2 Multisystem</a></div>
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