75 lines
5.6 KiB
HTML
75 lines
5.6 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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<html lang="en-us" xml:lang="en-us">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name="security" content="public" />
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<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))' />
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<meta name="DC.Type" content="reference" />
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<meta name="DC.Title" content="Temporary bitmap" />
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<meta name="abstract" content="The temporary bitmap is a temporary object that allows the optimizer to sequence rows based upon their row address (their row number). The bitmap can be either scanned or probed by the optimizer to satisfy different operations of the query." />
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<meta name="description" content="The temporary bitmap is a temporary object that allows the optimizer to sequence rows based upon their row address (their row number). The bitmap can be either scanned or probed by the optimizer to satisfy different operations of the query." />
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<meta name="DC.subject" content="definitions, temporary bitmap access method, temporary bitmap, access method, bitmap, access method" />
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<meta name="keywords" content="definitions, temporary bitmap access method, temporary bitmap, access method, bitmap, access method" />
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<meta name="DC.Relation" scheme="URI" content="rzajqtempobj.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzajqbitscan.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzajqbitprobe.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Identifier" content="rzajqtempbit" />
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<meta name="DC.Language" content="en-us" />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Temporary bitmap</title>
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</head>
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<body id="rzajqtempbit"><a name="rzajqtempbit"><!-- --></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">Temporary bitmap</h1>
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<div><p>The temporary bitmap is a temporary object that allows the optimizer
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to sequence rows based upon their row address (their row number). The bitmap
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can be either scanned or probed by the optimizer to satisfy different operations
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of the query.</p>
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<div class="section"><p>A temporary bitmap is a data structure that uses a bitmap to represent
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all of the row numbers for a table. Since each row is represented by a separate
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bit, all of the rows within a table can be represented in a fairly condensed
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form. When a row is selected by the temporary, the bit within the bitmap that
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corresponds to the selected row is set on. After the temporary bitmap is populated,
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all of the selected rows can be retrieved in a sorted manner for quick and
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efficient retrieval. The temporary only represents the row number for the
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associated selected rows. No table data is present within the temporary, so
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a table probe operation is typically associated with this temporary
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in order to retrieve the underlying table data. Because the bitmap is by
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definition sorted, the random I/O associated with the table probe operation
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can be performed more efficiently. The database manager will perform pre-fetch
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or look ahead logic to determine if multiple rows are located on adjacent
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pages. If so, the table probe will request a larger I/O to bring the rows
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into main memory more efficiently. </p>
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</div>
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<div class="section"><p>A temporary bitmap is an internal data structure and can only
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be created by the database manager.</p>
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</div>
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<div class="section"><p>Visual explain icon:</p>
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</div>
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<div class="section"><br /><img src="rzajq526.gif" alt="Temporary bitmap icon" /><br /></div>
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</div>
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<div>
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<ul class="ullinks">
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<li class="ulchildlink"><strong><a href="rzajqbitscan.htm">Bitmap scan</a></strong><br />
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During a bitmap scan operation, the entire temporary bitmap is scanned and all of the row addresses contained within the bitmap will be processed. A bitmap scan is generally considered when the optimizer is considering a plan that involves an encoded vector index or if the cost of the random I/O associated with an index probe or scan operation can be reduced by first preprocessing and sorting the row numbers associated with the Table Probe operation.</li>
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<li class="ulchildlink"><strong><a href="rzajqbitprobe.htm">Bitmap probe</a></strong><br />
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A bitmap probe operation is used to test row numbers generated by a separate operation against the selected rows of a temporary bitmap. The row numbers can be generated by any operation that constructs a row number for a table. That row number is then used to probe into a temporary bitmap to determine if that row number matches the selection used to generate the temporary bitmap.</li>
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</ul>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzajqtempobj.htm" title="Temporary objects are created by the optimizer in order to process a query. In general, these temporary objects are internal objects and cannot be accessed by a user.">Temporary objects and access methods</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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