80 lines
5.4 KiB
HTML
80 lines
5.4 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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<meta name="DC.Title" content="Control how the system runs the Open Query File (OPNQRYF) command" />
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<meta name="abstract" content="The optimization function allows you to specify how you are going to use the results of the query." />
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<meta name="description" content="The optimization function allows you to specify how you are going to use the results of the query." />
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<meta name="DC.subject" content="Open Query File (OPNQRYF) command, using, results of a query, OPNQRYF (Open Query File) command, results of a query, example, running the OPNQRYF command" />
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<meta name="DC.Relation" scheme="URI" content="rbafosropenex1.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<title>Control how the system runs the Open Query File (OPNQRYF) command</title>
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</head>
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<body id="rbafosropn"><a name="rbafosropn"><!-- --></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 how the system runs the Open Query File (OPNQRYF) command</h1>
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<div><p>The optimization function allows you to specify how you are going
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to use the results of the query.</p>
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<p>When you use the Open Query File (OPNQRYF) command, there are two steps
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where performance considerations exist. The first step is during the actual
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processing of the OPNQRYF command itself. This step decides if the OPNQRYF
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command is going to use an existing access path or build a new one for this
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query request. The second step when performance considerations play a role
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is when the application program is using the results of the OPNQRYF command
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to process the data.</p>
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<p>For most batch type functions, you are usually only interested in the total
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time of both steps mentioned in the preceding paragraph. Therefore, the default
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for the OPNQRYF command is OPTIMIZE(*ALLIO). This means that the OPNQRYF command
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considers the total time it takes for both steps.</p>
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<p>If you use the OPNQRYF command in an interactive environment, you might
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not be interested in processing the entire file. You might want the first
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screen full of records to be displayed as quickly as possible. For this reason,
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you want the first step to avoid building an access path, if possible. You
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can specify OPTIMIZE(*FIRSTIO) in such a situation.</p>
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<p>If you want to process the same results of the OPNQRYF command with multiple
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programs, you might want the first step to make an efficient open data path
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(ODP). That is, you try to minimize the number of records that must be read
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by the processing program in the second step by specifying OPTIMIZE(*MINWAIT)
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on the OPNQRYF command.</p>
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<p>If the KEYFLD or GRPFLD parameter on the OPNQRYF command requires that
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an access path be built when there is no access path to share, the access
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path is built entirely regardless of the OPTIMIZE entry. Optimization mainly
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affects selection processing.</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="rbafosropenex1.htm">Example 1: Control how the system runs the Open Query File (OPNQRYF) command</a></strong><br />
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This example shows how to optimize for the first set of records.</li>
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<li class="ulchildlink"><strong><a href="rbafosropenex2.htm">Example 2: Control how the system runs the Open Query File command</a></strong><br />
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This example shows how to optimize to minimize the number of records read.</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="rbafodynrs.htm" title="Dynamic record selection allows you to request a subset of the records in a file without using data description specifications (DDS).">Select records without using DDS</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="../rzajq/rzajqkickoff.htm">Database performance and query optimization</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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