134 lines
10 KiB
HTML
134 lines
10 KiB
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<meta name="DC.Title" content="iSeries server as the source server for DDM" />
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<meta name="abstract" content="When an application program or user in a source server job first refers to a DDM file, several actions occur as part of processing the request on the source server." />
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>iSeries server as the source
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server for DDM</title>
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</head>
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<body id="rbae5xs3xsrc"><a name="rbae5xs3xsrc"><!-- --></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"><span class="keyword">iSeries server</span> as the source
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server for DDM</h1>
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<div><p>When an application program or user in a source server job first
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refers to a DDM file, several actions occur as part of processing the request
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on the source server.</p>
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<p>All of these actions, as well as those required on the target server, must
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complete successfully before any operations (file or nonfile) requested by
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the source program can be done. When the DDM file is referred to:</p>
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<ul><li>If the request is to open a file, its information is used simultaneously
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to create an open data path (ODP) on the source server and to start the SDDM
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support, which runs within the same job as the source program. The SDDM also
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uses the information: to convert the source server request into a DDM request,
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to communicate with the appropriate target server, and to establish a DDM
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conversation to be used for the source job. (The ODP is partially created
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with the DDM file information; it is not usable until the SDDM processes the
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remaining information after the DDM conversation is established.)</li>
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<li>The communications portion of DDM establishes a communications path with
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the target server. The target <em>server</em> is identified by using the remote
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location information specified in the DDM file, and the target <em>file</em> is
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identified by the remote file name. Other information about e remote location,
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not kept in the DDM file, is stored by the SDDM. This includes
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the transaction program name, user ID, activation group number, and scope
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of the conversation. Using the remote location information, the TDDM is started
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on the target server and a DDM conversation is established when the remote
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server receives the program start request. The conversation is established
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the first time the remote file is accessed, but only if a conversation using
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the same remote location values for that target server does not already exist
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for the source job.</li>
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<li>After the DDM conversation is established, the SDDM (which can be used
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by multiple programs and multiple DDM files in the same source job) sends
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the DDM architecture command to the TDDM, for file-related requests. This
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command describes the file operation to be done and contains the name of the
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remote file (specified in the DDM file) to be accessed. For nonfile-related
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requests, such as when the <span class="cmdname">Submit Remote Command (SBMRMTCMD)</span> command
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is used, the remote file name is not sent to the TDDM; the remote file name
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is ignored.</li>
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</ul>
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<p>The SDDM converts each program request for a file open or input/output
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operation (received by using the DDM file and ODP) into an equivalent DDM
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command request and then sends it to the target server.</p>
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<p>The following figure shows the basic parts on the source <span class="keyword">iSeries™ server</span> that
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are involved in accessing remote files.</p>
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<div class="fignone" id="rbae5xs3xsrc__rbae5s3xsrc"><a name="rbae5xs3xsrc__rbae5s3xsrc"><!-- --></a><span class="figcap">Figure 1. <span class="keyword">iSeries server</span> as
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the DDM source server</span><br /><img src="rsll105.gif" alt="The parts involved in accessing remote files are the user application program, the open data path, SDDM, DDM Communications manager, and the target system." /><br /></div>
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<p>After each request is handled by the target job, the DDM response from
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the target server is returned, converted by the SDDM into the appropriate
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form, and passed back to the user. The response might include data (if data
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was requested) or an indication of status (for other types of file access).
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The source program waits until the function completes and the results are
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received.</p>
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<p>The following figure shows a simplified example of the interchange of data
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between the source and target servers for a typical request to access a remote
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file.</p>
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<div class="fignone" id="rbae5xs3xsrc__rbae5iorqst"><a name="rbae5xs3xsrc__rbae5iorqst"><!-- --></a><span class="figcap">Figure 2. Typical handling of an I/O operation
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request</span><br /><img src="rsll115.gif" alt="The handling of an I/O Operation Request proceeds as follows: Source system opens DDM file;, target system opens the remote file; the source system gets a record by key for later change; target system accesses, locks, and sends the record; source system modifies the record and requests a change; the target system changes the record and releases the lock; the source system closes the DDM file; the target system closes the remote file." /><br /></div>
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<p>After the first DDM file that was opened in the job is closed, the DDM
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conversation that it used is normally kept active. This allows the same program
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or another program in the job to use the same conversation when opening another
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DDM file, or doing other DDM-related operations. (For example, in <a href="rbae5jobcnvs.htm#rbae5jobcnvs__rbae5jobfig">Figure 1</a>,
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source job 3A has two DDM files using the same conversation.) This saves the
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time and resources required to establish a new conversation every time a new
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DDM file that uses the same remote location information is used in that job.</p>
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<p>When a DDM file is closed, the DDM conversation remains active, but nothing
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happens in the conversation until the SDDM processes the next DDM-related
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request from a program. While it is not being used, however, the conversation
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can be dropped. This can occur if the DDMCNV job attribute's default value
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of *KEEP is changed to *DROP using the <span class="cmdname">Change Job (CHGJOB</span>)
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command, or if the<span class="cmdname"> Reclaim DDM Conversations (RCLDDMCNV)</span> command
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or <span class="cmdname">Reclaim Resources (RCLRSC)</span> command is used while the
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job is active. </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="rbae5ile1.htm">Integrated Language Environment and DDM</a></strong><br />
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Integrated
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Language Environment<sup>®</sup> (ILE) introduces the concept of activation groups
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that run within jobs on the <span class="keyword">iSeries server</span>.</li>
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<li class="ulchildlink"><strong><a href="rbae5srcsvraction.htm">Source server actions dependent on type of target server</a></strong><br />
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If the target server is not another <span class="keyword">iSeries server</span> or <span class="keyword">System/38™</span>, only the DDM architecture
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commands defined in Level 2.0 and earlier of the DDM architecture are used.</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="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="rbae5partsddm.htm" title="The support on the source (or local) iSeries server is started, as needed, within a source job to do DDM functions.">Parts of DDM: Source DDM</a></div>
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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="rbae5ddmcnv.htm" title="The DDMCNV parameter is a job-related parameter that controls whether Advanced Program-to-Program Communication (APPC) or iSeries conversations in the job that is allocated for DDM use (that is, DDM conversations) are to be automatically dropped or kept active for the source job.">DDMCNV parameter considerations</a></div>
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<div><a href="rbae5ctlcnv.htm" title="Normally, the DDM conversations associated with a source server job are kept active until one of the conditions described in this topic is met.">Control DDM conversations</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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