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<meta name="DC.Title" content="Control DDM conversations" />
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<meta name="abstract" content="The term connection in this topic collection refers to the concept of an SQL connection. An SQL connection lasts from the time an explicit or implicit SQL CONNECT is done until the logical SQL connection is terminated by such means as an SQL DISCONNECT, or a RELEASE followed by a COMMIT." />
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<meta name="DC.subject" content="connection, SQL versus network, conversations, SNA versus TCP/IP, communications, DDM conversations, distributed data management (DDM), keeping conversations, dropping conversations, DDM (distributed data management), keeping conversations, dropping conversations, keeping conversations active, DDM (distributed data management), SQL statement, DISCONNECT, RELEASE, distributed data management (DDM), unused conversations, dropped conversations, unused conversations, dropped conversations, DDMCNV job attribute, DDMCNV (DDM conversations) job attribute, keeping conversations active, keeping conversations active, command, RCLRSC (Reclaim Resources), Reclaim Resources (RCLRSC), command, CL, Reclaim Resources (RCLRSC), resources, reclaiming, RCLDDMCNV (Reclaim Distributed Data Management Conversations), Reclaim Distributed Data Management Conversations (RCLDDMCNV), RCLDDMCNV (Reclaim Distributed Data Management Conversations), Reclaim Distributed Data Management Conversations (RCLDDMCNV), distributed data management conversations, CHGJOB, CHGJOB (Change Job), Change Job (CHGJOB), CHGJOB (Change Job), Change Job (CHGJOB), job, changing" />
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<title>Control DDM conversations</title>
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<body id="rbal1ddmcnv"><a name="rbal1ddmcnv"><!-- --></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">Control DDM conversations</h1>
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<div><p>The term <em>connection</em> in this topic collection refers to the
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concept of an SQL connection. An SQL connection lasts from the time an explicit
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or implicit SQL CONNECT is done until the logical SQL connection is terminated
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by such means as an SQL DISCONNECT, or a RELEASE followed by a COMMIT.</p>
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<div class="section"> <p>Multiple SQL connections can occur serially over a single network
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connection or conversation. In other words, when a connection is ended, the
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conversation that carried it is not necessarily ended.</p>
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<div class="note"><span class="notetitle">Note:</span> The term <em>conversation</em> has
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a specific, technical meaning in SNA APPC terminology. It does not extend
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to TCP/IP terminology in a formal sense. However, there is a similar concept
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in TCP/IP (a 'network connection' in other topics on the subject). In this
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topic collection, the word is used with the understanding that it applies
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to TCP/IP network connections as well. In other topics of this topic collection,
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the term retains its specific APPC meaning, but it is expected that the reader
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can discern that meaning from the context. </div>
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</div>
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<div class="section"><p>When an application requester (AR) uses DRDA<sup>®</sup> to connect to an application server
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(AS), it uses a DDM conversation. The conversation is established with the
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SQL CONNECT statement from the AR, but only if: </p>
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<ul><li>A conversation using the same remote location values does not already
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exist for the AR job.</li>
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<li>A conversation uses the same activation group.</li>
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<li>If started from DDM, a conversation has the file scoped to the activation
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group.</li>
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<li>A conversation has the same conversation type (protected or unprotected).</li>
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</ul>
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<p>DDM conversations can be in one of three states: active, unused,
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or dropped. A DDM conversation used by the distributed relational database
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is active while the AR is connected to the AS.</p>
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</div>
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<div class="section"><p>The SQL DISCONNECT and RELEASE statements are used to end connections.
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Connections can also be ended implicitly by the server. In addition, when
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running with RUW connection management, previous connections are ended when
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a CONNECT is performed. </p>
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<p>After a connection ends, the DDM conversations
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then either become unused or are dropped. If a DDM conversation is unused,
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the conversation to the remote database management system is maintained by
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the DDM communications manager and marked as unused. If a DDM conversation
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is dropped, the DDM communications manager ends the conversation. The DDMCNV
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job attribute determines whether DDM conversations for connections that are
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no longer active become unused or dropped. If the job attribute value is *KEEP
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and the connection is to another <span class="keyword">iSeries™ server</span>,
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the conversation becomes unused. If the job attribute value is *DROP or the
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connection is not to another <span class="keyword">iSeries server</span>,
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the conversation is dropped.</p>
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</div>
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<div class="section"><p>Using a DDMCNV job attribute of *KEEP is desirable when connections
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to remote relational databases are frequently changed.</p>
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</div>
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<div class="section"><p>A value of *DROP is desirable in the following situations:</p>
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<ul><li>When the cost of maintaining the conversation is high and the conversation
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will not be used relatively soon.</li>
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<li>When running with a mixture of programs compiled with RUW connection management
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and programs compiled with DUW connection management. Attempts to run programs
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compiled with RUW connection management to remote locations will fail when
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protected conversations exist.</li>
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<li>When running with protected conversations either with DDM or DRDA. Additional
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overhead is incurred on commits and rollbacks for unused protected conversations.</li>
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</ul>
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</div>
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<div class="section"><p>If a DDM conversation is also being used to operate on remote
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files through DDM, the conversation will remain active until the following
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conditions are met:</p>
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<ul><li>All the files used in the conversation are closed and unlocked</li>
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<li>No other DDM-related functions are being performed</li>
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<li>No DDM-related function has been interrupted (by a break program, for
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example)</li>
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<li>For protected conversations, a commit or rollback was performed after
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ending all SQL programs and after all DDM-related functions were completed</li>
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<li>An AR job is no longer connected to the AS</li>
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</ul>
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</div>
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<div class="section"><p>Regardless of the value of the DDMCNV job attribute, conversations
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are dropped at the end of a job routing step, at the end of the job, or when
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the job initiates a <span class="cmdname">Reroute Job (RRTJOB)</span> command. Unused
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conversations within an active job can also be dropped by the <span class="cmdname">Reclaim
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DDM Conversations (RCLDDMCNV)</span> or <span class="cmdname">Reclaim Resources (RCLRSC)</span> command.
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Errors, such as communications line failures, can also cause conversations
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to drop. </p>
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</div>
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<div class="section"><p>The DDMCNV parameter is changed by the <span class="cmdname">Change Job (CHGJOB)</span> command
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and is displayed by <span class="cmdname">Display Job (DSPJOB)</span> command with OPTION(*DFNA).
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Also, you can use the <span class="cmdname">Retrieve Job Attributes (RTVJOBA)</span> command
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to get the value of this parameter and use it within a CL program.</p>
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</div>
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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="rbal1reclaim.htm">Reclaim DDM resources</a></strong><br />
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The <span class="cmdname">Reclaim Distributed Data Management Conversations
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(RCLDDMCNV)</span> command reclaims all application conversations that
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are not currently being used by a source job, even if the DDMCNV attribute
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value for the job is *KEEP.</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="rbal1admin.htm" title="As an administrator for a distributed relational database, you are responsible for work being done on several servers.">Administration</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="../cl/chgjob.htm">Change Job (CHGJOB) command</a></div>
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<div><a href="../cl/dspjob.htm">Display Job (DSPJOB) command</a></div>
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<div><a href="rbal1excon.htm" title="The CONNECT statement is used to explicitly connect an application requester (AR) to an identified application server (AS). This SQL statement can be embedded within an application program or you can issue it using Interactive SQL.">Explicit connection management</a></div>
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<div><a href="rbal1reclaim.htm" title="The Reclaim Distributed Data Management Conversations (RCLDDMCNV) command reclaims all application conversations that are not currently being used by a source job, even if the DDMCNV attribute value for the job is *KEEP.">Reclaim DDM resources</a></div>
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<div><a href="../cl/rclrsc.htm">Reclaim Resources (RCLRSC) command</a></div>
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<div><a href="../cl/rrtjob.htm">Reroute Job (RRTJOB) command</a></div>
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<div><a href="../cl/rtvjoba.htm">Retrieve Job Attributes (RTVJOBA) command</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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