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130 lines
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<meta name="DC.Title" content="DDM-related jobs and DDM conversations" />
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<meta name="abstract" content="This topic provides additional information about activation groups, source server jobs, target server jobs, and the DDM conversations used by those jobs." />
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<title>DDM-related jobs and DDM conversations</title>
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<body id="rbae5jobcnvs"><a name="rbae5jobcnvs"><!-- --></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">DDM-related jobs and DDM conversations</h1>
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<div><p>This topic provides additional information about activation groups,
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source server jobs, target server jobs, and the DDM conversations used by
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those jobs.</p>
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<p>For remote file processing, at least two separate jobs are used, one running
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on each server: a source job and a target job. (The source server job is the
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one in which the user application is running.) Multiple application programs
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can be running in different activation groups within a single source job.
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Each activation group within a source job has a separate DDM conversation
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and target job for the remote location information specified in the DDM files.
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Multiple DDM files share a conversation when the following items are true:</p>
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<ul><li>The files are accessed in the same activation group within a source job.</li>
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<li>The files specify the same remote location combination.</li>
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</ul>
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<p>For each DDM conversation, there is one target job, which includes the
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TDDM.</p>
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<p>The SDDM runs within a source job or activation group on the source server.
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It can handle multiple DDM conversations with one or more target servers at
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the same time. For the same source job or activation group, one SDDM handles
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all the remote file access requests. This is true regardless of how many target
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servers or remote files are involved. No separate job for the SDDM exists
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in the server.</p>
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<p>If the source server DDM files involved all use the same remote location
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information to identify the target server, one TDDM job is created for each
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source server job that requests access to one or more files on the target
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server.</p>
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<p>The following figure shows five programs accessing six DDM files. The numbers
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in the upper set of boxes representing DDM files correspond to the same numbers
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in the lower set of boxes representing the associated remote files. These
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DDM files are using four different remote location descriptions to access
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six different remote files, all on the same target server. Seven DDM conversations
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are needed to handle the processing. An explanation of the DDM conversations
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follows:</p>
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<ul><li>PGM1 and PGM2 run in different source jobs and are using DDM files (2
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and 3) that contain the same remote location information. A separate conversation
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is needed for each source job.</li>
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<li>PGM3 in source job 3 uses the two DDM files (5 and 6) that both use the
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same remote location information. They will share the same conversation and
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target job (5B).</li>
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<li>PGM4 and PGM5 run in different activation groups within source job 4.
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They are using two DDM files (5 and 6) that both use the same remote location
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information. A separate conversation is needed for each activation group.</li>
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</ul>
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<p>In the following figure, jobs 1, 2, and 3 in System A each have a SDDM.
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Each activation group in job 4 has its own SDDM. Jobs 1B through 7B each have
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their own TDDM. </p>
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<div class="p">When the application program or the source job closes the DDM file on the
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source server, the DDM conversation and its associated target job ends, unless
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the following items are true: <ul><li>The value of the DDMCNV attribute of the <span class="cmdname">Change Job (CHGJOB)</span> command
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for the source job is *KEEP (the server default).</li>
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<li>Any locks established during the job by the <span class="cmdname">Allocate Object (ALCOBJ)</span> command
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still exist.</li>
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</ul>
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</div>
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<div class="fignone" id="rbae5jobcnvs__rbae5jobfig"><a name="rbae5jobcnvs__rbae5jobfig"><!-- --></a><span class="figcap">Figure 1. Relationships of DDM source
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and target jobs</span><br /><img src="rsll118.gif" alt="This figure is described in the preceding text." /><br /></div>
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<p>The <span class="cmdname">CHGJOB</span> and <span class="cmdname">ALCOBJ</span> commands are
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described in topic Use CL and DDS with DDM. If DDMCNV(*KEEP) is specified,
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the DDM conversation remains active and waits for another DDM request to be
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started.</p>
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<p>From a performance viewpoint, if the DDM conversation is likely to be used
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again, *KEEP is the value that should be used. This saves the time and resources
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used on the target server to start each TDDM and establish the conversation
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and job.</p>
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<p>The following figure shows the relationship between the SDDM and two TDDMs
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on <em>different</em> target servers and the figure in Example: Access
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files on multiple servers with DDM topic shows the relationship between the
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SDDM and two TDDMs on <em>one</em> target server.</p>
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<p>An <span class="keyword">iSeries™ server</span> can be a source
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server and a target server at the same time, and two servers can be accessing
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files located on each other. In addition, an <span class="keyword">iSeries</span> job
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can be a source job and a target job. A DDM file can refer to a remote file
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that is another DDM file.</p>
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<div class="fignone" id="rbae5jobcnvs__rbae5srctgt3"><a name="rbae5jobcnvs__rbae5srctgt3"><!-- --></a><span class="figcap">Figure 2. Example: Access multiple local
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and remote files</span>. <span class="figdesc">An <span class="keyword">iSeries server</span> with
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communications links to a <span class="keyword">System/38™</span> and
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to a <span class="keyword">System/36™</span>.</span><br /><img src="rsll107.gif" alt="An iSeries with communications links to a System/38 and to a System/36." /><br /></div>
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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="rbae5advcncp.htm" title="Most users of DDM will not need the information in the remainder of these topics; it is intended primarily for experienced programmers who need to know more about DDM.">Additional DDM concepts</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="rbae5cldsp.htm" title="This topic contains DDM-related information about specific iSeries control language (CL) commands, data description specifications (DDS) considerations, DDS keywords, and DDM user profile authority.">Use CL and DDS with DDM</a></div>
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</div>
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<div class="relref"><strong>Related reference</strong><br />
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<div><a href="rbae5exampleacc.htm" title="This topic contains a figure which shows the relationships among the source server, its DDM files, and two target servers.">Example: Access files on multiple servers with DDM</a></div>
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<div><a href="rbae5addcons.htm" title="This topic describes additional considerations for the SBMRMTCMD command.">Additional considerations: SBMRMTCMD command</a></div>
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</div>
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<div class="relinfo"><strong>Related information</strong><br />
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<div><a href="../books/sc415606.pdf " target="_blank">ILE Concepts</a></div>
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</div>
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</div>
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</body>
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