71 lines
4.6 KiB
HTML
71 lines
4.6 KiB
HTML
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<meta name="DC.Title" content="Fine-tune record-blocking" />
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<meta name="abstract" content="Record-blocking is a technique that significantly reduces the number of network flows." />
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<title>Fine-tune record-blocking</title>
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</head>
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<body id="odbcfinetunercdblock"><a name="odbcfinetunercdblock"><!-- --></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">Fine-tune record-blocking</h1>
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<div><p><strong>Record-blocking</strong> is a technique that significantly reduces
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the number of network flows. </p>
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<div class="section"><p>It does this by returning a <em>block</em> of rows from the server
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on the first FETCH request for a cursor. Subsequent FETCH requests are retrieved
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from the local block of rows, rather then going to the server each time. This
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technique dramatically increases performance when it is properly used. The
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default settings should be sufficient for most situations.</p>
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</div>
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<div class="section"><p>A change to one of the record-blocking parameters can make a significant
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difference when the performance of your environment is approaching the exponential
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threshold that is illustrated in <a href="rzaikintrocsperf.htm#introcsperf">Introduction to client/server performance</a>.
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For example, assume that an environment has <em>n</em> decision-support clients
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doing some amount of work with large queries, typically returning 1 MB of
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data. </p>
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</div>
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<div class="section"><p>At the opposite extreme is a scenario where users consistently
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ask for large amounts of data, but typically never examine more than a few
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rows. The overhead of returning 32KB of rows when only a few are needed could
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degrade performance. Setting the <em>BLOCKSIZE</em> or <em>BlockSizeKB</em> connection
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string keyword to a lower value, setting the <em>BLOCKFETCH</em> connection
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string keyword to 0 (Use ODBC blocking) or disabling record blocking altogether,
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might actually increase performance.</p>
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</div>
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<div class="section"><p>It is important to note that, as always in client/server, performance
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results may vary. You might make changes to these parameters and not realize
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any difference. This may indicate that your performance bottleneck is not
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the client request queue at the server. This parameter gives you one more
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tool to use when your users start objecting.</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="rzaikodbcperfarch.htm" title="For the iSeries Access for Windows ODBC driver, all of the internal data flows between the client and the server are chained together, and transmit only when needed.">The performance architecture of the iSeries Access for Windows ODBC driver</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="rzaikconnstrkeywordsperfprop.htm" title="Use these iSeries Access ODBC driver connection string keywords to change Performance properties of the ODBC connection.">Connection string keywords - Performance properties</a></div>
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</div>
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</div>
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</body>
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</html> |