92 lines
5.8 KiB
HTML
92 lines
5.8 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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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.Type" content="reference" />
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<meta name="DC.Title" content="Monitoring background statistics collection" />
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<meta name="abstract" content="The system value QDBFSTCCOL controls who is allowed to create statistics in the background." />
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<meta name="description" content="The system value QDBFSTCCOL controls who is allowed to create statistics in the background." />
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<meta name="DC.subject" content="statistics manager, monitoring background statistics collection" />
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<meta name="keywords" content="statistics manager, monitoring background statistics collection" />
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<meta name="DC.Relation" scheme="URI" content="../rzakz/rzakzqdbfstccol.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Monitoring background statistics collection</title>
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</head>
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<body id="monitorstats"><a name="monitorstats"><!-- --></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">Monitoring background statistics collection</h1>
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<div><p>The system value QDBFSTCCOL controls who is allowed to create statistics
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in the background.</p>
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<div class="section"><div class="p">The following list provides the possible values: <dl><dt class="dlterm"><span class="synph"><span class="kwd">*ALL</span></span></dt>
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<dd>Allows all statistics to be collected in the background. This is the default
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setting.</dd>
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<dt class="dlterm"><span class="synph"><span class="kwd">*NONE</span></span></dt>
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<dd>Restricts everyone from creating statistics in the background. This does
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not prevent immediate user-requested statistics from being collected, however.</dd>
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<dt class="dlterm"><span class="synph"><span class="kwd">*USER</span></span></dt>
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<dd>Allows only user-requested statistics to be collected in the background.</dd>
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<dt class="dlterm"><span class="synph"><span class="kwd">*SYSTEM</span></span></dt>
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<dd>Allows only system-requested statistics to be collected in the background.</dd>
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</dl>
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</div>
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</div>
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<div class="section"><p>When you switch the system value to something other than *ALL
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or *SYSTEM, the Statistics Manager continues to place statistics requests
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in the Plan Cache. When the system value is switched back to *ALL, for example,
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background processing analyzes the entire Plan Cache and looks for any column
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statistics requests that are there. This background task also identifies column
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statistics that have been used by an plan in the Plan Cache and determines
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if these column statistics have become stale. Requests for the new column
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statistics as well as requests for refresh of the stale columns statistics
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are then executed.</p>
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</div>
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<div class="section"><p>All background statistic collections initiated by the system or
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submitted to the background by a user are performed by the system job QDBFSTCCOL
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(user-initiated immediate requests are run within the user's job). This job
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uses multiple threads to create the statistics. The number of threads is determined
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by the number of processors that the system has. Each thread is then associated
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with a request queue.</p>
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</div>
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<div class="section"><p>There are four types of request queues based on who submitted
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the request and how long the collection is estimated to take. The default
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priority assigned to each thread can determine to which queue the thread belongs: </p>
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<ul><li>Priority 90 — short user requests</li>
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<li>Priority 93 — long user requests</li>
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<li>Priority 96 — short system requests</li>
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<li>Priority 99 — long system requests</li>
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</ul>
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</div>
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<div class="section"><p>Background statistics collections attempt to use as much parallelism
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as possible. This parallelism is independent of the SMP feature installed
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on the iSeries™.
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However, parallel processing is allowed only for immediate statistics collection
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if SMP is installed on the system and the job requesting the column statistics
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is set to allow parallelism.</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="statsmanager.htm" title="As stated earlier, the collection of statistics is handled by a separate component called the Statistics Manager. Statistical information can be used by the query optimizer to determine the best access plan for a query. Since the query optimizer bases its choice of access plan on the statistical information found in the table, it is important that this information be current.">Collecting statistics with the Statistics Manager</a></div>
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</div>
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<div class="relinfo"><strong>Related information</strong><br />
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<div><a href="../rzakz/rzakzqdbfstccol.htm">Allow background database statistics collection (QDBFSTCCOL) system value</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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