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110 lines
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<meta name="DC.Title" content="Create Node Group (CRTNODGRP) command" />
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<meta name="abstract" content="This section uses two CL command examples to show how to create a node group by using the Create Node Group (CRTNODGRP) command." />
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<title>Create Node Group (CRTNODGRP) command</title>
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<body id="crtngc"><a name="crtngc"><!-- --></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">Create Node Group (CRTNODGRP) command</h1>
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<div><p>This section uses two CL command examples to show how to create
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a node group by using the Create Node Group (CRTNODGRP) command.</p>
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<div class="p">In the following example, a node group with default partitioning (equal
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partitioning across the systems) is created: <pre>CRTNODGRP NODGRP(LIB1/GROUP1) RDB(SYSTEMA SYSTEMB SYSTEMC SYSTEMD)
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TEXT('Node group for test files')</pre>
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</div>
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<p>In this example, the command creates a node group that contains four nodes.
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Note that each of the nodes must be defined RDB entries (previously added
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to the relational database directory using the ADDRDBDIRE command) and that
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one node must be defined as local (*LOCAL).</p>
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<p>The partitioning attributes default to assigning one-fourth of the partitions
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to each node number. This node group can be used on the NODGRP parameter of
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the Create Physical File (CRTPF) command to create a distributed file. For
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more information about distributed files, see Creating distributed files with DB2<sup>®</sup> Multisystem.</p>
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<div class="p">In the following example, a node group with specified partitioning is created
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by using the partitioning file (PTNFILE) parameter: <pre>CRTNODGRP NODGRP(LIB1/GROUP2) RDB(SYSTEMA SYSTEMB SYSTEMC)
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PTNFILE(LIB1/PTN1)
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TEXT('Partition most of the data to SYSTEMA')</pre>
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</div>
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<p>In this example, the command creates a node group that contains three nodes
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(SYSTEMA, SYSTEMB, and SYSTEMC). The partitioning attributes are taken from
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the file called PTN1. This file can be set up to force a higher percentage
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of the records to be located on a particular system.</p>
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<p>The file PTN1 in this example is a partitioning file. This file is not
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a distributed file, but a regular local physical file that can be used to
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set up a custom partitioning scheme. The partitioning file must have one 2-byte
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binary field. The partitioning file must contain 1024 records in which each
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record contains a valid node number.</p>
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<div class="fignone" id="crtngc__ftn1"><a name="crtngc__ftn1"><!-- --></a><span class="figcap">Figure 1. Example of the contents of partitioning file PTNFILE</span><br /><img src="rbal3508.gif" alt="In this graphic of a partitioning file with a 2–byte binary field, Row 1 corresponds to partition number 0, and Row 1024 corresponds to partition number 1023." /><br /></div>
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<p>If the node group contains three nodes, all of the records in the partitioning
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file must have numbers 1, 2, or 3. The node numbers are assigned in the order
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that the RDB names were specified on the Create Node Group (CRTNODGRP) command.
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A higher percentage of data can be forced to a particular node by having more
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records containing that node number in the partitioning file. This is a method
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for customizing the partitioning with respect to the amount of data that physically
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resides on each system. To customize the partitioning with respect to specific
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values residing on specific nodes, use the Change Node Group Attributes (CHGNODGRPA)
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command. See Changing node groups using the CHGNODGRPA command with DB2 Multisystem
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for more information.</p>
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<p>You should note that, because the node group information is stored in the
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distributed file, the file is not immediately sensitive to changes in the
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node group or to changes in the RDB directory entries that are included in
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the node group. You can make modifications to node groups and RDB directory
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entries, but until you use the CHGPF command and specify the changed node
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group, your files do not change their behavior.</p>
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<p>Another concept is that of a <em>visibility node</em>. A
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visibility node within a node group contains the file object (part of the
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mechanism that allows the file to be distributed across several nodes), but
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no data. A visibility node retains a current level of the file object at all
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times; the visibility node has no data stored on it. In contrast, a node (sometimes
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called a <em>data node</em>) contains data. As an example of how you can use
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a visibility node in your node group, assume that the <span class="keyword">iSeries™</span> server
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that your sales executives use is part of your node group. These executives
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probably do not want to run queries on a regular basis, but on occasion they
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might want to run a specific query. From their server, they can run their
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queries, access real-time data, and receive the results of their query. So
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even though none of the data is stored on their server, because their system
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is a visibility node, the executives can run the query whenever necessary.</p>
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<p>To specify a node as being a visibility node, you must use the PTNFILE
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parameter on the Create Node Group (CRTNODGRP) command. If the partitioning
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file contains no records for a particular node number, that node is a visibility
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node.</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="nodework.htm" title="A node group is a system object (*NODGRP), which is stored on the system on which it was created.">How node groups work with DB2 Multisystem</a></div>
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<div><a href="crtdf.htm" title="A distributed file is a database file that is spread across multiple iSeries servers.">Distributed files with DB2 Multisystem</a></div>
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<div><a href="chgnga.htm" title="The Change Node Group Attributes (CHGNODGRPA) command changes the data partitioning attributes for a node group.">Change Node Group Attributes (CHGNODGRPA) command</a></div>
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</div>
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</div>
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