79 lines
5.9 KiB
HTML
79 lines
5.9 KiB
HTML
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<meta name="DC.Title" content="Factors that affect the size of DRDA query blocks" />
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<meta name="abstract" content="If a large amount of data is being returned on a query, performance might be improved by increasing the size of the block of query data. How this is done depends on the types of servers participating in the query." />
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<title>Factors that affect the size of DRDA query blocks</title>
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</head>
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<body id="rbal1factor"><a name="rbal1factor"><!-- --></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">Factors that affect the size of DRDA<sup>®</sup> query blocks</h1>
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<div><p>If a large amount of data is being returned on a query, performance
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might be improved by increasing the size of the block of query data. How this
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is done depends on the types of servers participating in the query.</p>
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<div class="section"><p>In an unlike environment, the size of the query block is determined
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at the application requester by a parameter sent with the <span class="cmdname">Open Query</span> command.
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When an <span class="keyword">iSeries™ server</span> is the application
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requester (AR), it always initially requests a query block size of 32 KB.
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It increases the size of each successive requested query block for large queries
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that require multiple blocks to transmit. Other types of ARs give the user
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a choice of what block size to use. The default query block sizes for DB2<sup>®</sup> Universal
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Driver for SQLJ and JDBC, DB2 Universal Database™ for z/OS<sup>®</sup>, DB2
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Universal Database™ for VM, and <span>DB2 Universal Database for Linux<sup>®</sup>, UNIX<sup>®</sup> and Windows<sup>®</sup></span> are
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32 KB, 32 KB, 8 KB, and 32 KB, respectively. See the product documentation
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for the platform being used as an AR when a <span class="keyword">DB2 Universal Database for iSeries</span> server
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is connected to an unlike AR.</p>
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</div>
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<div class="section"><p>In the <span class="keyword">DB2 UDB for iSeries</span> to <span class="keyword">DB2 UDB for iSeries</span> environment, the query block
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size is determined by the size of the buffer used by the database manager.
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The default size is 4 KB. This can be changed on application servers that
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are at the version 2 release 3, or later. In order to do this, use the <span class="cmdname">Submit
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Remote Command (SBMRMTCMD)</span> command to send and execute an <span class="cmdname">Override
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with Database File (OVRDBF)</span> command on the application server (AS).
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Besides the name of the file being overridden, the (<span class="cmdname">OVRDBF</span>)
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command should contain OVRSCOPE(*JOB) and SEQONLY(*YES nnn). The number of
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records desired per block replaces nnn in the SEQONLY parameter. Increasing
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the size of the database buffer not only can reduce communications overhead,
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but can also reduce the number of calls to the database manager to retrieve
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the rows.</p>
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</div>
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<div class="section"><p>You can also change the query block size using an SQL CALL statement
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(a stored procedure) from non-<span class="keyword">iSeries server</span>s
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or between <span class="keyword">iSeries server</span>s.</p>
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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="rbal1improveviadata.htm" title="Distributed relational database performance is affected by the overall design of the database. The location of distributed data, the level of commitment control you use, and the design of your SQL indexes all affect performance.">Improve distributed relational database performance through the database</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="../cl/sbmrmtcmd.htm">Submit Remote Command (SBMRMTCMD) command</a></div>
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<div><a href="../cl/ovrdbf.htm">Override with Database File (OVRDBF) command</a></div>
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</div>
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</div>
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</body>
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