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<meta name="abstract" content="The Plan Cache contains a wealth of information about the SQE queries being run through the database. Its contents are viewable through the iSeries Navigator GUI interface." />
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<title>Viewing the plan cache with iSeries Navigator</title>
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<img src="./delta.gif" alt="Start of change" /><!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Viewing the plan cache with iSeries™ Navigator</h1>
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<div><p>The Plan Cache contains a wealth of information about the SQE queries
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being run through the database. Its contents are viewable through the iSeries
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Navigator GUI interface.</p>
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<div class="section"><p>This Plan Cache interface provides a window into the database
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query operations on the system. The interface to the Plan Cache resides under
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the <span class="menucascade"><span class="uicontrol">iSeries Navigator</span> > <span class="uicontrol">system
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name</span> > <span class="uicontrol">Database</span></span>.</p>
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</div>
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<div class="section"><img src="rzajq558.gif" alt="iSeries Navigator - SQL Plan Cache
Snapshots" /></div>
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<div class="section"><p>Clicking the SQL Plan Cache folder shows a list of any snapshots
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gathered so far. A snapshot is a database monitor file generated from the
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plan cache and can be treated very much the same as the SQL Performance Monitors
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list. The same analysis capability exists for snapshots as exists for traditional
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SQL performance monitors. </p>
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<p>By right-clicking the SQL Plan Cache icon,
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a series of options are shown which allow different views of current plan
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cache of the database. The <span class="menucascade"><span class="uicontrol">SQL Plan Cache</span> > <span class="uicontrol">Show Statements</span></span> option brings up a screen
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with filtering capability. This screen provides a direct view of the current
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plan cache on the system. </p>
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</div>
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<div class="section"><img src="rzajq559.gif" alt="iSeries Navigator - SQL Plan Cache
statements" /></div>
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<div class="section"><p>Note that the retrieve action needs to be performed (pushed) to
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fill the display. The information shown shows the SQL query text, the last
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time the query was run, the most expensive single instance run of the query,
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total processing time consumed by the query, total number of times the query
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has been run and information about the user and job that first created the
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plan entry. It also shows how many times (if any) that the database engine
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was able to reuse the results of a prior run of the query to avoid rerunning
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the entire query.</p>
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<p>The screen also provides filtering options which allow
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the user to more quickly isolate specific criteria of interest. No filters
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are required to be specified (the default), though adding filtering will shorten
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the time it takes to show the results. The list of queries that is returned
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is ordered by default so that those consuming the most processing time are
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shown at the top. You can reorder the results by clicking on the column heading
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for which you want the list ordered. Repeated clicking toggles the order from
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ascending to descending. When an individual entry is chosen, more detailed
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information about that entry can be seen. <strong>Show Longest Runs</strong> shows details
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of up to ten of the longest running instances of that query. <strong>Run Visual
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Explain</strong> can also be performed against the chosen query to show the details
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of the query plan. Finally, if one or more entries are highlighted, a snapshot
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(database performance monitor file) for those selected entries can be generated.</p>
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<p>The
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information presented can be used in multiple ways to help with performance
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tuning. For example, Visual Explain of key queries can be utilized to show
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advice for creating an index to improve those queries. Alternatively, the
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longest running information can be used to determine if the query is being
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run during a heavy utilization period and can potentially be rescheduled to
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a more opportune time.</p>
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<p>One item to note is that the user and job name
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information given for each entry is the user and job that initially caused
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the creation of the cached entry (the user where full optimization took place).
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This is not necessarily the same as the last user to run that query.</p>
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<p>The
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filtering options provide a way to focus in on a particular area of interest:</p>
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<dl><dt class="dlterm">Minimum runtime for the longest execution</dt>
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<dd>Filter to those queries with at least one long individual query instance
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runtime</dd>
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<dt class="dlterm">Queries run after this date and time</dt>
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<dd>Filters to those queries that have been run recently</dd>
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<dt class="dlterm">Top 'n' most frequently run queries</dt>
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<dd>Finds those queries run most often.</dd>
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<dt class="dlterm">Top 'n' queries with the largest total accumulated runtime</dt>
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<dd>Shows the top resource consumers. This equates to the first n entries
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shown by default when no filtering is given. Specifying a value for n improves
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the performance of getting the first screen of entries, though the total entries
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displayed is limited to n.</dd>
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<dt class="dlterm">Queries ever run by user</dt>
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<dd>Provides a way to see the list of queries a particular user has run. Note
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that if this filter is specified, the user and job name information shown
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in the resulting entries still reflect the originator of the cached entry,
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which is not necessarily the same as the user specified on the filter.</dd>
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<dt class="dlterm">Queries currently active</dt>
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<dd>Shows the list of cached entries associated with queries that are still
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running or are in pseudo close mode. As with the user filtering, the user
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and job name information shown in the resulting entries still reflects the
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originator of the cached entry, which is not necessarily the same as the user
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currently running the query (there may be multiple users running the query). <div class="note"><span class="notetitle">Note:</span> Current
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SQL for a job (right-click the Database icon) is an alternative for the viewing
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a particular job's active query.</div>
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</dd>
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<dt class="dlterm">Queries with index advised</dt>
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<dd>Limits the list to those queries where an index was advised by the optimizer
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to improve performance.</dd>
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<dt class="dlterm">Queries with statistics advised</dt>
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<dd>Limits the list to those queries where a statistic not yet gathered might
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have been useful to the optimizer if it was collected. The optimizer automatically
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gathers these statistics in the background, so this option is normally not
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that interesting unless, for whatever reason, you want to control the statistics
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gathering yourself.</dd>
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<dt class="dlterm">Include queries initiated by the operating system</dt>
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<dd>includes into the list the 'hidden' queries initiated by the database
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itself behind the scenes to process a request. By default the list only includes
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user initiated queries.</dd>
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<dt class="dlterm">Queries that use or reference these objects</dt>
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<dd>Provides a way to limit the entries to those that referenced or use the
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table(s) or index(s) specified.</dd>
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<dt class="dlterm">SQL statement contains</dt>
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<dd>Provides a wildcard search capability on the SQL text itself. It is useful
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for finding particular types of queries. For example, queries with a FETCH
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FIRST clause can be found by specifying ‘fetch’. The search is case insensitive
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for ease of use. For example, the string 'FETCH' will find the same entries
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as the search string 'fetch'.</dd>
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</dl>
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<p>Multiple filter options can be specified. Note that in a
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multi-filter case, the candidate entries for each filter are computed independently
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and only those entries that are present in all the candidate lists are shown.
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So, for example, if you specified options <strong>Top 'n' most frequently run queries</strong> and <strong>Queries
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ever run by user</strong>, you will be shown those most-run entries in the cache
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that happen to have been run at some point by the specified user. You will
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not necessarily be shown the most frequently run queries run by the user (unless
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those queries also happen to be the most frequently run queries in the entire
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cache). </p>
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<p>The <span class="menucascade"><span class="uicontrol">SQL Plan Cache</span> > <span class="uicontrol">Properties</span></span> option shows high level information about the cache, including
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for example, cache size, number of plans, number of full open and pseudo opens
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that have occurred.</p>
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</div>
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<div class="section"><img src="rzajq560.gif" alt="iSeries Navigator - SQL Plan Cache
Properties" /></div>
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<div class="section"><p>This information can be used to view overall database activity.
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If tracked over time, it provides trends to help you better understand the
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database utilization peaks and valleys throughout the day and week.</p>
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<p>The <span class="menucascade"><span class="uicontrol">New</span> > <span class="uicontrol">Snapshot</span></span> option
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allows for the creation of a snapshot from the plan cache. Unlike the snapshot
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option under Show Statements, it allows you to create a snapshot without having
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to first view the queries. </p>
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</div>
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<div class="section"><img src="rzajq561.gif" alt="" /></div>
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<div class="section"><p>The same filtering options are provided here as on the Show Statements
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screen.</p>
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<p>The stored procedure, qsys2.dump_plan_cache, provides
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the simplest way to create a database monitor file output (snapshot) from
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the plan cache. The dump_plan_cache procedure takes two parameters, library
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name and file name, for identifying the resulting database monitor file. If
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the file does not exist, it is created. For example, to dump the plan cache
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to a database performance monitor file in library QGPL:</p>
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<pre><strong>CALL</strong> qsys2.dump_plan_cache('QGPL','SNAPSHOT1');</pre>
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</div>
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<div class="section"><p>Note that the plan cache is an actively changing cache. Therefore,
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it is important to realize that it contains timely information. If information
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over long periods of time is of interest, consider implementing a method of
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performing periodic snapshots of the plan cache to capture trends and heavy
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usage periods. The APIs described above, used in conjunction with job scheduling
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(for example), can be used to programmatically perform periodic snapshots.</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 class="relconcepts"><strong>Related concepts</strong><br />
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<div><a href="rzajqcache.htm" title="The Plan Cache is a repository that contains the access plans for queries that were optimized by SQE.">Plan Cache</a></div>
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</div>
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