<?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="Optimizer" /> <meta name="abstract" content="Optimizer is an important module of the i5/OS Query component because it makes the key decisions for good database performance. Its main objective is to find the most efficient access path to the data." /> <meta name="description" content="Optimizer is an important module of the i5/OS Query component because it makes the key decisions for good database performance. Its main objective is to find the most efficient access path to the data." /> <meta name="DC.Relation" scheme="URI" content="rzaiksqlperf.htm" /> <meta name="DC.Relation" scheme="URI" content="costest.htm" /> <meta name="DC.Relation" scheme="URI" content="optdecrules.htm" /> <meta name="copyright" content="(C) Copyright IBM Corporation 1999, 2006" /> <meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1999, 2006" /> <meta name="DC.Format" content="XHTML" /> <meta name="DC.Identifier" content="optimizer" /> <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>Optimizer</title> </head> <body id="optimizer"><a name="optimizer"><!-- --></a> <!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script> <h1 class="topictitle1">Optimizer</h1> <div><p>Optimizer is an important module of the <span class="keyword">i5/OS™</span> Query component because it makes the key decisions for good database performance. Its main objective is to find the most efficient access path to the data.</p> <div class="section"><p>Query optimization is a trade-off between the time spent to select a query implementation and the time spent to run it. Query optimization must handle the following distinct user needs: </p> <ul><li>Quick interactive response</li> <li>Efficient use of total-machine resources</li> </ul> </div> <div class="section"><p>In deciding how to access data, Optimizer does the following: </p> <ul><li>Determines possible implementations</li> <li>Picks the optimal implementation for the <span class="keyword">i5/OS</span> Query component to execute</li> </ul> </div> </div> <div> <ul class="ullinks"> <li class="ulchildlink"><strong><a href="costest.htm">Cost estimation</a></strong><br /> At runtime, the Optimizer chooses an optimal access method for the query by calculating an implementation cost based on the current state of the database.</li> <li class="ulchildlink"><strong><a href="optdecrules.htm">Optimizer decision-making rules</a></strong><br /> In performing its function, Optimizer uses a general set of guidelines to choose the best method for accessing data.</li> </ul> <div class="familylinks"> <div class="parentlink"><strong>Parent topic:</strong> <a href="rzaiksqlperf.htm" title="Good application design includes the efficient use of machine resources. To run in a manner that is acceptable to the end user, an application program must be efficient in operation, and must run with adequate response time.">SQL performance</a></div> </div> </div> </body> </html>