77 lines
4.8 KiB
HTML
77 lines
4.8 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="User index considerations" />
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<meta name="abstract" content="The performance of a user index is much better than that of a database file. However, before using a user index, you must know the functional differences between a user index and a database file." />
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<meta name="description" content="The performance of a user index is much better than that of a database file. However, before using a user index, you must know the functional differences between a user index and a database file." />
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<meta name="DC.Relation" scheme="URI" content="concept.htm" />
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<meta name="DC.Relation" scheme="URI" content="../apis/jc1.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="conIndexCons" />
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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> User index considerations</title>
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</head>
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<body id="conIndexCons"><a name="conIndexCons"><!-- --></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"> User index considerations</h1>
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<div><p>The performance of a user index is much better than that of a database
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file. However, before using a user index, you must know the functional differences
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between a user index and a database file.</p>
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<p>The contents of a database file are not affected by an abnormal system
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end. On the other hand, the contents of a user index may become totally unusable
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if the system ends abnormally. Therefore, you should not use a user index
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if the information you want to store needs to remain without errors after
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an abnormal system end.</p>
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<p>If your system abnormally ends when you are removing or inserting a user
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index entry, unpredictable results may occur. If you are inserting or removing
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a user index entry and you should force the index entry to the disk unit using
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one of the following:</p>
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<ul><li>A user index created with the immediate update parameter set to 1 (affects
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performance)</li>
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<li>A modify index (MODIDX) MI instruction with the immediate update bit set
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to 1</li>
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<li>The set access state (SETACST) MI instruction</li>
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</ul>
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<p>If you do not force the index entry and the system abnormally ends, your
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index will probably be damaged.</p>
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<p>To determine if your last system power down was normal or abnormal, you
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can check the system value QABNORMSW.</p>
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<p>You will not get an error message if your index is damaged. The definition
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of your index is usable; it is probably the data in your index that is bad.</p>
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<p>You can log changes to a database file in a journal, and you can use the
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journal to apply or remove those changes later. You can also use the journal
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to audit who is using the database file. However, the system does not support
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the journaling of indexes. As a result, user applications should log entries
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in a journal to keep track of changes to the index, but you cannot update
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the index using apply and remove journal entry functions. For more information
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on journaling, see the Journal and Commit APIs.</p>
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<p>Indexes support the storage of data that does not need to remain after
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an abnormal system end. If an abnormal system end does occur, you must use
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a backup copy of the index that was previously saved or create a new copy
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of the index.</p>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="concept.htm" title="Describes the underlying concepts that you need to understand to work effectively with APIs. Among the concepts covered are basic concepts, programming considerations, and terminology.">API concepts</a></div>
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</div>
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<div class="relref"><strong>Related reference</strong><br />
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<div><a href="../apis/jc1.htm">Journal and Commit APIs</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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