91 lines
4.9 KiB
HTML
91 lines
4.9 KiB
HTML
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<meta name="DC.Title" content="When will query data be blocked for better performance?" />
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<meta name="abstract" content="The query data will be blocked if none of these conditions are true." />
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<title>When will query data be blocked for better performance?</title>
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</head>
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<body id="rbal1ques2"><a name="rbal1ques2"><!-- --></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">When will query data be blocked for better performance?</h1>
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<div><p>The query data will be blocked if none of these conditions are
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true.</p>
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<div class="section"><ul><li>The cursor is updatable (see note 1).</li>
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<li>The cursor is potentially updatable (see note 2).</li>
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<li>The BLOCKING NO precompiler or bind option was used on SQLPREP or SQLBIND.</li>
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</ul>
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</div>
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<div class="section"><p>Unless you force single-row protocol with the BLOCKING NO precompile/bind
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option, blocking will occur in both of the following cases:</p>
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<ul><li>The cursor is read-only (see note 3).</li>
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<li>All of the following are true: <ul><li>There is no FOR UPDATE OF clause in the SELECT, and</li>
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<li>There are no UPDATE or DELETE WHERE CURRENT OF statements against the
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cursor in the program, and</li>
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<li>Either the program does not contain dynamic SQL statements or BLOCKING
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ALL was used.</li>
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</ul>
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</li>
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</ul>
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</div>
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<div class="section"> <div class="note"><span class="notetitle">Notes:</span> <ol><li>A cursor is updatable if it is not read-only (see note 3), and one of
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the following items is true: <ul><li>The select statement contained the FOR UPDATE OF clause, or</li>
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<li>There exists in the program an UPDATE or DELETE WHERE CURRENT OF against
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the cursor.</li>
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</ul>
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</li>
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<li>A cursor is potentially updatable if it is not read-only (see note 3),
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and if the program includes any dynamic statement, and the BLOCKING UNAMBIG
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precompile or bind option was used on SQLPREP or SQLBIND.</li>
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<li>A cursor is read-only if one or more of the following conditions is true:
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<ul><li>The DECLARE CURSOR statement specified an ORDER BY clause but did not
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specify a FOR UPDATE OF clause.</li>
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<li>The DECLARE CURSOR statement specified a FOR FETCH ONLY clause.</li>
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<li>One or more of the following conditions are true for the cursor or a view
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or logical file referenced in the outer subselect to which the cursor refers:
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<ul><li>The outer subselect contains a DISTINCT keyword, GROUP BY clause, HAVING
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clause, or a column function in the outer subselect.</li>
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<li>The select contains a join function.</li>
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<li>The select contains a UNION operator.</li>
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<li>The select contains a subquery that refers to the same table as the table
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of the outer-most subselect.</li>
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<li>The select contains a complex logical file that had to be copied to a
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temporary file.</li>
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<li>All of the selected columns are expressions, scalar functions, or constants.</li>
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<li>All of the columns of a referenced logical file are input only.</li>
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</ul>
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</li>
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</ul>
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</li>
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</ol>
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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="rbal1xplat.htm" title="This topic collection concentrates on describing iSeries support for distributed relational databases in a network of iSeries servers (a like environment).">User FAQs</a></div>
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</div>
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</div>
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</body>
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