120 lines
7.2 KiB
HTML
120 lines
7.2 KiB
HTML
|
<?xml version="1.0" encoding="UTF-8"?>
|
||
|
|
<!DOCTYPE html
|
||
|
|
PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
|
||
|
|
<html lang="en-us" xml:lang="en-us">
|
||
|
|
<head>
|
||
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
|
||
|
|
<meta name="security" content="public" />
|
||
|
|
<meta name="Robots" content="index,follow" />
|
||
|
|
<meta http-equiv="PICS-Label" content='(PICS-1.1 "http://www.icra.org/ratingsv02.html" l gen true r (cz 1 lz 1 nz 1 oz 1 vz 1) "http://www.rsac.org/ratingsv01.html" l gen true r (n 0 s 0 v 0 l 0) "http://www.classify.org/safesurf/" l gen true r (SS~~000 1))' />
|
||
|
|
<meta name="DC.Type" content="reference" />
|
||
|
|
<meta name="DC.Title" content="Sorted list scan" />
|
||
|
|
<meta name="abstract" content="During a sorted list scan operation, the entire temporary sorted list is scanned and all of the entries contained within the sorted list will be processed." />
|
||
|
|
<meta name="description" content="During a sorted list scan operation, the entire temporary sorted list is scanned and all of the entries contained within the sorted list will be processed." />
|
||
|
|
<meta name="DC.subject" content="definitions, sorted list scan access method, temporary sorted list, scan access method, sorted list scan, access method" />
|
||
|
|
<meta name="keywords" content="definitions, sorted list scan access method, temporary sorted list, scan access method, sorted list scan, access method" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rzajqtempslist.htm" />
|
||
|
|
<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
|
||
|
|
<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1998, 2006" />
|
||
|
|
<meta name="DC.Format" content="XHTML" />
|
||
|
|
<meta name="DC.Identifier" content="rzajqslistscan" />
|
||
|
|
<meta name="DC.Language" content="en-us" />
|
||
|
|
<!-- All rights reserved. Licensed Materials Property of IBM -->
|
||
|
|
<!-- US Government Users Restricted Rights -->
|
||
|
|
<!-- Use, duplication or disclosure restricted by -->
|
||
|
|
<!-- GSA ADP Schedule Contract with IBM Corp. -->
|
||
|
|
<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
|
||
|
|
<link rel="stylesheet" type="text/css" href="./ic.css" />
|
||
|
|
<title>Sorted list scan</title>
|
||
|
|
</head>
|
||
|
|
<body id="rzajqslistscan"><a name="rzajqslistscan"><!-- --></a>
|
||
|
|
<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
|
||
|
|
<h1 class="topictitle1">Sorted list scan</h1>
|
||
|
|
<div><p>During a sorted list scan operation, the entire temporary sorted
|
||
|
|
list is scanned and all of the entries contained within the sorted list will
|
||
|
|
be processed. </p>
|
||
|
|
<div class="section"><p>A sorted list scan is generally considered when the optimizer
|
||
|
|
is considering a plan that requires the data values to be sequenced. The use
|
||
|
|
of a sorted list scan will allow the optimizer to generate a plan that can
|
||
|
|
take advantage of any non-join selection while creating the temporary sorted
|
||
|
|
list. An additional benefit of using a sorted list scan is that the data structure
|
||
|
|
of the temporary sorted list will usually cause the table data within the
|
||
|
|
sorted list to remain resident within main memory after creation thus reducing
|
||
|
|
paging on the subsequent sorted list scan operation.</p>
|
||
|
|
</div>
|
||
|
|
<div class="section">
|
||
|
|
<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" frame="border" border="1" rules="all"><caption>Table 1. Sorted list scan attributes</caption><thead align="left"><tr><th valign="top" width="31.313131313131315%" id="d0e41">Data access method</th>
|
||
|
|
<th valign="top" width="68.68686868686868%" id="d0e43">Sorted list scan</th>
|
||
|
|
</tr>
|
||
|
|
</thead>
|
||
|
|
<tbody><tr><td valign="top" width="31.313131313131315%" headers="d0e41 "><strong>Description</strong></td>
|
||
|
|
<td valign="top" width="68.68686868686868%" headers="d0e43 ">Read all of the entries in a temporary sorted list.
|
||
|
|
The sorted list may perform distinct processing to eliminate duplicate values
|
||
|
|
or take advantage of the temporary sorted list to sequence all of the rows.</td>
|
||
|
|
</tr>
|
||
|
|
<tr><td valign="top" width="31.313131313131315%" headers="d0e41 "><strong>Advantages</strong></td>
|
||
|
|
<td valign="top" width="68.68686868686868%" headers="d0e43 "><ul><li>Reduces the random I/O to the table generally associated with longer running
|
||
|
|
queries that would otherwise use an index to sequence the data.</li>
|
||
|
|
<li>Selection can be performed prior to generating the sorted list to subset
|
||
|
|
the number of rows in the temporary object</li>
|
||
|
|
</ul>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr><td valign="top" width="31.313131313131315%" headers="d0e41 "><strong>Considerations</strong></td>
|
||
|
|
<td valign="top" width="68.68686868686868%" headers="d0e43 ">Generally used to process ordering or distinct processing.
|
||
|
|
Can perform poorly when the entire sorted list does not stay resident in memory
|
||
|
|
as it is being populated and processed. </td>
|
||
|
|
</tr>
|
||
|
|
<tr><td valign="top" width="31.313131313131315%" headers="d0e41 "><strong>Likely to be used</strong></td>
|
||
|
|
<td valign="top" width="68.68686868686868%" headers="d0e43 "><ul><li>When the use of temporary results is allowed by the query environmental
|
||
|
|
parameter (ALWCPYDTA)</li>
|
||
|
|
<li>When the data is required to be ordered based upon a column or columns
|
||
|
|
for ordering or distinct processing</li>
|
||
|
|
</ul>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr><td valign="top" width="31.313131313131315%" headers="d0e41 "><strong>Example SQL statement</strong></td>
|
||
|
|
<td valign="top" width="68.68686868686868%" headers="d0e43 "> <pre>CREATE INDEX X1 ON Employee (LastName, WorkDept)
|
||
|
|
|
||
|
|
SELECT * FROM Employee
|
||
|
|
WHERE WorkDept BETWEEN 'A01' AND 'E01'
|
||
|
|
ORDER BY FirstNme
|
||
|
|
OPTIMZE FOR ALL ROWS</pre>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr><td valign="top" width="31.313131313131315%" headers="d0e41 "><strong>Messages indicating use</strong></td>
|
||
|
|
<td valign="top" width="68.68686868686868%" headers="d0e43 ">There are multiple ways in which a sorted list scan
|
||
|
|
can be indicated through the messages. The messages in this example illustrate
|
||
|
|
how the SQL Query Engine will indicate a sorted list scan was used. <ul><li>Optimizer Debug: <pre>CPI4328 -- Access path of file X1 was used by query.
|
||
|
|
CPI4325 -- Temporary result file built for query.</pre>
|
||
|
|
</li>
|
||
|
|
<li>PRTSQLINF: <pre>SQL4008 -- Index X1 used for table 1.
|
||
|
|
SQL4002 -- Reusable ODP sort used.</pre>
|
||
|
|
</li>
|
||
|
|
</ul>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr><td valign="top" width="31.313131313131315%" headers="d0e41 "><strong>SMP parallel enabled</strong></td>
|
||
|
|
<td valign="top" width="68.68686868686868%" headers="d0e43 ">No</td>
|
||
|
|
</tr>
|
||
|
|
<tr><td valign="top" width="31.313131313131315%" headers="d0e41 "><strong>Also referred to as</strong></td>
|
||
|
|
<td valign="top" width="68.68686868686868%" headers="d0e43 ">Sorted List Scan, Preload <p>Sorted List Scan Distinct</p>
|
||
|
|
<p>Sorted
|
||
|
|
List Scan Distinct, Preload</p>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr><td valign="top" width="31.313131313131315%" headers="d0e41 "><strong>Visual Explain icon</strong></td>
|
||
|
|
<td valign="top" width="68.68686868686868%" headers="d0e43 "><br /><img src="rzajq519.gif" alt="Sorted list scan icon" /><br /></td>
|
||
|
|
</tr>
|
||
|
|
</tbody>
|
||
|
|
</table>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
<div>
|
||
|
|
<div class="familylinks">
|
||
|
|
<div class="parentlink"><strong>Parent topic:</strong> <a href="rzajqtempslist.htm" title="The temporary sorted list is a temporary object that allows the optimizer to sequence rows based upon a column or set of columns. The sorted list can be either scanned or probed by the optimizer to satisfy different operations of the query.">Temporary sorted list</a></div>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</body>
|
||
|
|
</html>
|