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<meta name="DC.Title" content="Testing performance with the query governor" />
<meta name="abstract" content="You can use the query governor to test the performance of your queries." />
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<h1 class="topictitle1">Testing performance with the query governor</h1>
<div><p>You can use the query governor to test the performance of your
queries.</p>
<div class="section"><p>To test the performance of a query with the query governor, do
the following:</p>
</div>
<div class="section"> <ol><li>Set the query time limit to zero ( QRYTIMLMT(0) ) using the <span class="cmdname">Change
Query Attributes (CHGQRYA)</span> command or in the INI file. This forces
an inquiry message from the governor stating that the estimated time to run
the query exceeds the query time limit.</li>
<li>Prompt for message help on the inquiry message and find the same information
that you can find by running the <span class="cmdname">Print SQL Information (PRTSQLINF)</span> command.</li>
</ol>
</div>
<div class="section"><p>The query governor lets you optimize performance without having
to run through several iterations of the query. </p>
</div>
<div class="section"><p>Additionally, if the query is canceled, the query optimizer evaluates
the access plan and sends the optimizer debug messages to the job log. This
occurs even if the job is <em>not</em> in debug mode. You can then review the
optimizer tuning messages in the job log to see if additional tuning is needed
to obtain optimal query performance. This allows you to try several permutations
of the query with different attributes, indexes, and syntax or both to determine
what performs better through the optimizer without actually running the query
to completion. This saves on system resources because the actual query of
the data is never actually done. If the tables to be queried contain a large
number of rows, this represents a significant savings in system resources.</p>
</div>
<div class="section"><p>Be careful when you use this technique for performance testing,
because all query requests will be stopped before they are run. This is especially
important for a CQE query that cannot be implemented in a single query step.
For these types of queries, separate multiple query requests are issued, and
then their results are accumulated before returning the final results. Stopping
the query in one of these intermediate steps gives you only the performance
information that relates to that intermediate step, and not for the entire
query.</p>
</div>
</div>
<div>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="govrle.htm" title="The DB2 Universal Database for iSeries Predictive Query Governor can stop the initiation of a query if the estimated run time (elapsed execution time) or estimated temporary storage for the query is excessive. The governor acts before a query is run instead of while a query is run. The governor can be used in any interactive or batch job on the iSeries. It can be used with all DB2 Universal Database for iSeries query interfaces and is not limited to use with SQL queries.">Set resource limits with the Predictive Query Governor</a></div>
</div>
<div class="relinfo"><strong>Related information</strong><br />
<div><a href="../cl/prtsqlinf.htm">Print SQL Information (PRTSQLINF) command</a></div>
<div><a href="../cl/chgqrya.htm">Change Query Attributes (CHGQRYA) command</a></div>
</div>
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