86 lines
6.2 KiB
HTML
86 lines
6.2 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 name="Robots" content="index,follow" />
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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="concept" />
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<meta name="DC.Title" content="Query Engine Overview" />
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<meta name="abstract" content="DB2 UDB for iSeries provides two query engines to process queries: the Classic Query Engine (CQE) and the SQL Query Engine (SQE)." />
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<meta name="description" content="DB2 UDB for iSeries provides two query engines to process queries: the Classic Query Engine (CQE) and the SQL Query Engine (SQE)." />
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<meta name="DC.subject" content="query engine overview" />
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<meta name="keywords" content="query engine overview" />
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<meta name="DC.Relation" scheme="URI" content="rzajqkickoff.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzajqsqecqe.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzajqdispatcher.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzajqstatsmgr.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzajqcache.htm" />
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<meta name="DC.Relation" scheme="URI" content="../rzajp/rzajpkickoff.htm" />
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<meta name="DC.Relation" scheme="URI" content="../sqlp/rbafykickoff.htm" />
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<meta name="DC.Relation" scheme="URI" content="../apis/qqqqry.htm" />
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<meta name="DC.Relation" scheme="URI" content="../cl/opnqryf.htm" />
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<meta name="DC.Relation" scheme="URI" content="../cl/runsqlstm.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="queryoptimize" />
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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>Query Engine Overview</title>
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</head>
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<body id="queryoptimize"><a name="queryoptimize"><!-- --></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">Query Engine Overview</h1>
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<div><p>DB2<sup>®</sup> UDB
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for iSeries™ provides
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two query engines to process queries: the Classic Query Engine (CQE) and the
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SQL Query Engine (SQE). </p>
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<p>The CQE processes queries originating from non-SQL interfaces: OPNQRYF,
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Query/400, and QQQQry API. SQL based interfaces, such as ODBC, JDBC, CLI,
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Query Manager, Net.Data<sup>®</sup>,
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RUNSQLSTM, and embedded or interactive SQL, run through the SQE. For ease
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of use, the routing decision for processing the query by either CQE or SQE
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is pervasive and under the control of the system. The requesting user or application
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program cannot control or influence this behavior. However, a better understanding
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of the engines and of the process that determines which path a query takes
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can lead you to a better understand of your query's performance. </p>
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<p>Along with the new query engine, several more components were created and
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other existing components were updated. Additionally, new data access methods
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were created for SQE. </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="rzajqsqecqe.htm">SQE and CQE Engines</a></strong><br />
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To fully understand the implementation of query management and
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processing in DB2 UDB
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for iSeries on <span class="keyword">i5/OS™</span> V5R2 and subsequent releases,
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it is important to see how the queries were implemented in releases of <span class="keyword">i5/OS™</span> previous to V5R2.</li>
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<li class="ulchildlink"><strong><a href="rzajqdispatcher.htm">Query Dispatcher</a></strong><br />
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The function of the Dispatcher is to route the query request to either CQE or SQE, depending on the attributes of the query. All queries are processed by the Dispatcher and you cannot bypass it.</li>
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<li class="ulchildlink"><strong><a href="rzajqstatsmgr.htm">Statistics Manager</a></strong><br />
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In releases before V5R2, the retrieval of statistics was a function of the Optimizer. When the Optimizer needed to know information about a table, it looked at the table description to retrieve the row count and table size. If an index was available, the Optimizer might then extract further information about the data in the table. In V5R2, the collection of statistics was removed from the Optimizer and is now handled by a separate component called the Statistics Manager.</li>
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<li class="ulchildlink"><strong><a href="rzajqcache.htm">Plan Cache</a></strong><br />
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The Plan Cache is a repository that contains the access plans for queries that were optimized by SQE.</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 class="relinfo"><strong>Related information</strong><br />
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<div><a href="../rzajp/rzajpkickoff.htm">Embedded SQL programming</a></div>
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<div><a href="../sqlp/rbafykickoff.htm">SQL programming</a></div>
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<div><a href="../apis/qqqqry.htm">Query (QQQQRY) API</a></div>
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<div><a href="../cl/opnqryf.htm">Open Query File (OPNQRYF) command</a></div>
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<div><a href="../cl/runsqlstm.htm">Run SQL Statements (RUNSQLSTM) command</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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