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93 lines
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<h1 class="topictitle1">Tips: Design distributed relational database applications</h1>
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<div><p>Distributed relational database applications have different requirements
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from applications developed solely for use on a local database.</p>
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<div class="section"><p> To properly plan for these differences, design your applications
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with the following considerations in mind: </p>
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</div>
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<div class="section"><div class="p"> <ul><li>Take advantage of the distributed unit of work (DUW) function where appropriate. <div class="note"><span class="notetitle">Note:</span> Before
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Version 5 Release 1 of OS/400<sup>®</sup>, two-phase commit support was not available
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with TCP/IP on the <span class="keyword">iSeries™</span> server.</div>
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</li>
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<li>Code programs using common interfaces.</li>
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<li>Consider dividing a complex application into smaller parts and placing
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each piece of the application in the location best suited to process it. One
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good way to distribute processing in an application is to make use of the
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SQL CALL statement to run a stored procedure at a remote location where the
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data to be processed resides. The stored procedure is not limited to SQL operations
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when it runs on a <span class="keyword">DB2 Universal Database™ for iSeries</span> application
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server; it can use integrated database input/output or perform other types
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of processing.</li>
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<li>Investigate how the initial database applications will be prepared, tested,
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and used.</li>
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<li>Take advantage, when possible, of SQL set-processing capabilities. This
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will minimize communication with the application servers. For example, update
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multiple rows with one SQL statement whenever you can.</li>
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<li>Be aware that database updates within a unit of work must be done at a
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single site if the remote unit of work (RUW) connection method is used when
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the programs are prepared, or if the other nodes in the distributed application
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do not support DUW.</li>
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<li>Keep in mind that the DUW connection method restricts you from directing
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a single statement to more than one relational database.</li>
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<li>Performance is affected by the choice of connection management methods.
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Use of the RUW connection management method might be preferable if you do
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not have the need to switch back and forth among different remote relational
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databases. This is because more overhead is associated with the two-phase
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commit protocols used with DUW connection management. <p>However, if you
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have to switch frequently among multiple remote database management systems,
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use DUW connection management. When running with DUW connection management,
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communication conversations to one database management system do not have
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to be ended when you switch the connection to another database management
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system. In the like environment, this is not as big a factor as in the unlike
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environment, since conversations in the like environment can be kept active
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by use of the default DDMCNV(*KEEP) job definition attribute. Even in the
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like environment, however, a performance advantage can be gained by using
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DUW to avoid the cost of closing cursors and sending the communication flow
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to establish a new connection.</p>
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</li>
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<li>The connection management method determines the semantics of the CONNECT
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statement. With the RUW connection management method, the CONNECT statement
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ends any existing connections before establishing a new connection to the
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relational database. With the DUW connection management method, the CONNECT
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statement does not end existing connections.</li>
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</ul>
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</div>
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</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="rbal1desappnet.htm" title="Designing a distributed relational database involves making choices about applications, network considerations, and data considerations.">Design the application, network, and data for a distributed relational database</a></div>
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