88 lines
5.6 KiB
HTML
88 lines
5.6 KiB
HTML
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<meta name="DC.Title" content="Examine query optimizer debug messages in the job log" />
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<meta name="abstract" content="Query optimizer debug messages issue informational messages to the job log about the implementation of a query. These messages explain what happened during the query optimization process." />
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<title>Examine query optimizer debug messages in the job log</title>
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<body id="qodm"><a name="qodm"><!-- --></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">Examine query optimizer debug messages in the job log</h1>
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<div><p>Query optimizer debug messages issue informational messages to
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the job log about the implementation of a query. These messages explain what
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happened during the query optimization process. </p>
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<div class="section"><p>For example, you can learn: </p>
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<ul><li>Why an index was or was not used</li>
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<li>Why a temporary result was required</li>
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<li>Whether joins and blocking are used</li>
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<li>What type of index was advised by the optimizer</li>
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<li>Status of the job's queries</li>
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<li>Indexes used</li>
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<li>Status of the cursor</li>
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</ul>
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</div>
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<div class="section"><p>The optimizer automatically logs messages for all queries it optimizes,
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including SQL, call level interface, ODBC, OPNQRYF, and SQL Query Manager.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Viewing debug messages using STRDBG command:</h4><p><span class="cmdname">STRDBG</span> command
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puts a job into debug mode. It also specifies certain attributes of the debugging
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session. For example, it can specify whether database files in production
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schemas can be updated while in debug mode. For example, use the following
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command: </p>
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<pre>STRDBG PGM(Schema/program) UPDPROD(*YES)</pre>
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<p><span class="cmdname">STRDBG</span> places
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in the job log information about all SQL statements that run.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Viewing debug messages using QAQQINI table:</h4><p>You
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can also set the QRYOPTLIB parameter on the <span class="cmdname">Change Query Attributes
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(CHGQRYA)</span> command to a user schema where the QAQQINI table exists.
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Set the parameter on the QAQQINI table to MESSAGES_DEBUG, and set the value
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to *YES. This option places query optimization information in the job log.
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Changes made to the QAQQINI table are effective immediately and will affect
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all users and queries that use this table. Once you change the MESSAGES_DEBUG
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parameter, all queries that use this QAQQINI table will write debug messages
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to their respective joblogs. Pressing F10 from the command Entry panel displays
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the message text. To see the second-level text, press F1 (Help). The second-level
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text sometimes offers hints for improving query performance.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Viewing debug messages in Run SQL Scripts:</h4><p>To view
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debug messages in Run SQL Scripts, from the <span class="uicontrol">Options</span> menu,
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select <span class="uicontrol">Include Debug Messages in Job Log</span>. Then from
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the <span class="uicontrol">View</span> menu, select <span class="uicontrol">Job Log</span>.
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To view detailed messages, double-click a message.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Viewing debug messages in Visual Explain:</h4><p>In Visual
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Explain, debug messages are always available. You do not need to turn them
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on or off. Debug messages appear in the lower portion of the window. You can
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view detailed messages by double-clicking on a message.</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="queryopt.htm" title="Query optimization is an iterative process. You can gather performance information about your queries and control the processing of your queries.">Optimizing query performance using query optimization tools</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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