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5.9 KiB
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104 lines
5.9 KiB
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<title>Summarization of DRDA blocking rules</title>
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<body id="rbal1blocksummary"><a name="rbal1blocksummary"><!-- --></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">Summarization of DRDA<sup>®</sup> blocking rules</h1>
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<div><div class="section"><p>In summary, what these rules (including the notes) say is that
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in the absence of certain special or unusual conditions, blocking will occur
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in both of the following cases:</p>
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<ul><li>It will occur if the cursor is read-only (see note 3) and if: <ul><li>Either the application requester or application server is a non-<span class="keyword">DB2 Universal Database™ for iSeries™</span>.</li>
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<li>Both the application requester and application server are <span class="keyword">DB2 Universal Database for iSeries</span> and
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ALWBLK(*ALLREAD) is specified and COMMIT(*ALL) is <strong>not</strong> specified.</li>
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</ul>
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</li>
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<li>It will occur if COMMIT(*ALL) was not specified and all of the following
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conditions are also 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 a precompile/bind
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option was used to request limited-block protocol (/K=ALL with <span>DB2
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Universal Database™ for Linux<sup>®</sup>, UNIX<sup>®</sup> and Windows<sup>®</sup></span>, ALWBLK(*ALLREAD) with DB2<sup>®</sup> UDB
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for iSeries,
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CURRENTDATA(NO) with DB2 Universal Database for z/OS<sup>®</sup>, SBLOCK
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with DB2
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Universal Database for VM). </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 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 an EXECUTE or EXECUTE IMMEDIATE statement (or
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when connected to a non-<span class="keyword">iSeries server</span>,
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any dynamic statement), and a precompile or bind option is used that caused
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the package default value to be single-row protocol. <ul><li>For <span class="keyword">DB2 Universal Database for iSeries</span>, this is
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the ALWBLK(*READ) precompile option (the default).</li>
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<li>For DB2,
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this is CURRENTDATA(YES) on BIND PACKAGE (the default).</li>
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<li>For DB2
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Universal Database for VM, this is the SBLOCK keyword on SQLPREP.</li>
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<li>For DB2 for OS/2<sup>®</sup> (DB2/2),
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this is /K=UNAMBIG on SQLPREP or SQLBIND (the default).</li>
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</ul>
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</li>
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<li>A cursor is read-only if one or more of the following conditions are 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>The DECLARE CURSOR statement specified the SCROLL keyword without DYNAMIC
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(<span class="keyword">i5/OS™</span> only).</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 (<span class="keyword">i5/OS</span> 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="rbal1facblk.htm" title="A very important performance factor is whether blocking occurs when data is transferred between the application requester (AR) and the application server (AS). A group of rows transmitted as a block of data requires much less communications overhead than the same data sent one row at a time.">Factors that affect blocking for DRDA</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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