80 lines
6.7 KiB
HTML
80 lines
6.7 KiB
HTML
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<!DOCTYPE html
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<meta name="DC.Title" content="How node groups work with DB2 Multisystem" />
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<meta name="abstract" content="A node group is a system object (*NODGRP), which is stored on the system on which it was created." />
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<meta name="DC.subject" content="node group, *NODGRP system object, partitioning, default partitioning, partition number, hash algorithm, default partitioning, system object, *NODGRP, CRTNODGRP (Create Node Group) command, changing data partitioning, Create Node Group (CRTNODGRP) command, command, CL, CRTNODGRP (Create Node Group), changing data partitioning, Create Node Group (CRTNODGRP), PTNFILE (partitioning file) parameter, partitioning file (PTNFILE) parameter, CHGNODGRPA (Change Node Group Attributes) command, Change Node Group Attributes (CHGNODGRPA) command, CHGNODGRPA (Change Node Group Attributes), Change Node Group Attributes (CHGNODGRPA), node group, changing" />
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<meta name="keywords" content="node group, *NODGRP system object, partitioning, default partitioning, partition number, hash algorithm, default partitioning, system object, *NODGRP, CRTNODGRP (Create Node Group) command, changing data partitioning, Create Node Group (CRTNODGRP) command, command, CL, CRTNODGRP (Create Node Group), changing data partitioning, Create Node Group (CRTNODGRP), PTNFILE (partitioning file) parameter, partitioning file (PTNFILE) parameter, CHGNODGRPA (Change Node Group Attributes) command, Change Node Group Attributes (CHGNODGRPA) command, CHGNODGRPA (Change Node Group Attributes), Change Node Group Attributes (CHGNODGRPA), node group, changing" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<title>How node groups work with DB2 Multisystem</title>
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</head>
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<body id="nodework"><a name="nodework"><!-- --></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">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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</div>
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</div>
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</body>
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</html>
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