83 lines
5.0 KiB
HTML
83 lines
5.0 KiB
HTML
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<title>CPI432F - Access path suggestion for file &1</title>
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</head>
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<body id="cpi432f"><a name="cpi432f"><!-- --></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">CPI432F - Access path suggestion for file &1</h1>
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<div>
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<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" frame="border" border="1" rules="all"><thead align="left"><tr valign="bottom"><th colspan="2" align="center" valign="bottom" id="d0e16">CPI432F</th>
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</tr>
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</thead>
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<tbody><tr valign="middle"><td valign="middle" width="26.02040816326531%" headers="d0e16 ">Message Text:</td>
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<td valign="middle" width="73.9795918367347%" headers="d0e16 ">Access path suggestion for file &1.</td>
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</tr>
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<tr valign="middle"><td valign="middle" width="26.02040816326531%" headers="d0e16 ">Cause Text:</td>
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<td valign="middle" width="73.9795918367347%" headers="d0e16 ">To improve performance the query optimizer is suggesting a permanent
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access path be built with the key fields it is recommending. The access path
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will access records from member &3 of file &1 in library &2.
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<p></p>
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In the list of key fields that follow, the query optimizer is
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recommending the first &10 key fields as primary key fields. The remaining
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key fields are considered secondary key fields and are listed in order of
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expected selectivity based on this query. Primary key fields are fields that
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significantly reduce the number of keys selected based on the corresponding
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selection predicate. Secondary key fields are fields that may or may not significantly
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reduce the number of keys selected. It is up to the user to determine the
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true selectivity of secondary key fields and to determine whether those key
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fields should be used when creating the access path. <p></p>
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The query
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optimizer is able to perform key positioning over any combination of the primary
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key fields, plus one additional secondary key field. Therefore it is important
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that the first secondary key field be the most selective secondary key field.
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The query optimizer will use key selection with any remaining secondary key
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fields. While key selection is not as fast as key positioning it can still
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reduce the number of keys selected. Hence, secondary key fields that are fairly
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selective should be included. When building the access path all primary key
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fields should be specified first followed by the secondary key fields which
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are prioritized by selectivity. The following list contains the suggested
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primary and secondary key fields: <p></p>
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&11. <p></p>
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If file &1
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in library &2 is a logical file then the access path should be built over
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member &9 of physical file &7 in library &8.</td>
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</tr>
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<tr valign="middle"><td valign="middle" width="26.02040816326531%" headers="d0e16 ">Recovery Text:</td>
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<td valign="middle" width="73.9795918367347%" headers="d0e16 ">If this query is run frequently, you may want to create the suggested
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access path for performance reasons. It is possible that the query optimizer
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will choose not to use the access path just created. <p></p>
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For more
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information, refer to <a href="rzajqdta.htm#rzajqdta">Data access on DB2 UDB for iSeries: data access paths and methods</a>.</td>
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</tr>
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</tbody>
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</table>
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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="pimes.htm" title="You can evaluate the structure and performance of the given SQL statements in a program using informational messages put in the job log by the database manager.">Query optimization performance information messages</a></div>
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</div>
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</body>
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