78 lines
5.3 KiB
HTML
78 lines
5.3 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 name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Data access on DB2 UDB for iSeries: data access paths and methods" />
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<meta name="abstract" content="Data access methods are used to process queries and access data." />
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<meta name="description" content="Data access methods are used to process queries and access data." />
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<meta name="DC.Relation" scheme="URI" content="spreaddata.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<title>Data access on DB2 UDB for iSeries:
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data access paths and methods</title>
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</head>
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<body id="rzajqdta"><a name="rzajqdta"><!-- --></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">Data access on <span class="keyword">DB2 UDB for iSeries™</span>:
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data access paths and methods</h1>
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<div><p>Data access methods are used to process queries and access data.</p>
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<p>In general, the query engine has two kinds of raw material with which to
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satisfy a query request: </p>
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<ul><li>The database objects that contain the data to be queries</li>
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<li>The executable instructions or operations to retrieve and transform the
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data into usable information</li>
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</ul>
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<p>There are actually only two types of permanent database objects that can
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be used as source material for a query — tables and indexes (binary radix
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and encoded vector indexes). In addition, the query engine may need to create
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temporary objects or data structures to hold interim results or references
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during the execution of an access plan. The <span class="keyword">DB2<sup>®</sup> UDB Symmetric Multiprocessing</span> feature
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provides the optimizer with additional methods for retrieving data that include
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parallel processing. Finally, the optimizer uses certain methods to manipulate
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these objects.</p>
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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="rzajqpermobj.htm">Permanent objects and access methods</a></strong><br />
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The database objects and access methods used by the query engine can be broken down into three basic types of operations that are used to manipulate the permanent and temporary objects -- Create, Scan, and Probe.</li>
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<li class="ulchildlink"><strong><a href="rzajqtempobj.htm">Temporary objects and access methods</a></strong><br />
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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.</li>
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<li class="ulchildlink"><strong><a href="rzajq1parallel.htm">Objects processed in parallel</a></strong><br />
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The <span class="keyword">DB2 UDB Symmetric Multiprocessing</span> feature
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provides the optimizer with additional methods for retrieving data that include
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parallel processing. Symmetrical multiprocessing (SMP) is a form of parallelism
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achieved on a single server where multiple (CPU and I/O) processors that share
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memory and disk resource work simultaneously toward achieving a single end
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result.</li>
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<li class="ulchildlink"><strong><a href="spreaddata.htm">Spreading data automatically</a></strong><br />
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DB2
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Universal Database™ for iSeries™ automatically spreads the data across the
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disk devices available in the auxiliary storage pool (ASP) where the data
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is allocated. This ensures that the data is spread without user intervention. </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="rzajqkickoff.htm" title="The goal of database performance tuning is to minimize the response time of your queries and to make the best use of your server's resources by minimizing network traffic, disk I/O, and CPU time. This goal can only be achieved by understanding the logical and physical structure of your data, understanding the applications used on your server, and understanding how the many conflicting uses of your database may impact database performance.">Performance and query optimization</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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