106 lines
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106 lines
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HTML
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<meta name="DC.Title" content="Index recovery" />
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<title>Index recovery</title>
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<body id="rbal1indexrec"><a name="rbal1indexrec"><!-- --></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">Index recovery</h1>
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<div><p>An index describes the order in which rows are read from a table.
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When indexes are recorded in the journal, the server can recover the index
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to avoid spending a significant amount of time rebuilding indexes during the
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IPL that follows an abnormal server end or during the vary on of an independent
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ASP after an abnormal vary off.</p>
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<div class="section"><p>When you journal tables, images of changes to the rows in the
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table are written to the journal. These row images are used to recover the
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table if the server, or independent ASP, ends abnormally. However, after an
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abnormal end, the server might find that indexes built over the table are
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not synchronized with the data in the table. If an access path and its data
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are not synchronized, the server must rebuild the index to ensure that the
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two are synchronized and usable.</p>
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</div>
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<div class="section"><p>When indexes are journaled, the server records images of the index
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in the journal to provide known synchronization points between the index and
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its data. By having that information in the journal, the server can recover
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both the data and the index, and ensure that the two are synchronized. In
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such cases, the lengthy time to rebuild the indexes can be avoided. </p>
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</div>
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<div class="section"><p>The <span class="keyword">iSeries™ server</span> provides
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several functions to assist with index recovery. All indexes on the server
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have a maintenance option that specifies when the index is maintained. SQL
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indexes are created with an attribute of *IMMED maintenance.</p>
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</div>
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<div class="section"><p>In the event of a power failure or abnormal server failure, indexes
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that are in the process of change might need to be rebuilt to make sure they
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agree with the data. All indexes on the server have a recovery option that
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specifies when the index should be rebuilt if necessary. All SQL indexes with
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an attribute of UNIQUE are created with a recovery attribute of *IPL, which
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means these indexes are rebuilt before the <span class="keyword">i5/OS™</span> licensed
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program has been started. All other SQL indexes are created with the *AFTIPL
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recovery attribute, which means they are rebuilt after the operating system
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has been started or after the independent ASP has varied on. During an IPL
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or vary on of an independent ASP, you can see a display showing indexes that
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need to be rebuilt and their recovery options, and you can override these
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recovery options.</p>
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</div>
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<div class="section"><p>SQL indexes are not journaled automatically. You can use the <span class="cmdname">Start
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Journal Access Path (STRJRNAP)</span> command to journal any index created
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by SQL operations. The server save and restore functions allow you to save
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indexes when a table is saved by using ACCPTH(*YES) on the <span class="cmdname">Save Object
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(SAVOBJ)</span> or <span class="cmdname">Save Library (SAVLIB)</span> command.
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If you must restore a table, there is no need to rebuild the indexes. Any
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indexes not previously saved and restored are automatically and asynchronously
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rebuilt by the database.</p>
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</div>
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<div class="section"><p>Before journaling indexes, you must start journaling for the tables
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associated with the index. In addition, you must use the same journal for
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the index and its associated table.</p>
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</div>
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<div class="section"><p>Index journaling is designed to minimize additional output operations.
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For example, the server writes the journal data for the changed row and the
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changed index in the same output operation. However, you should seriously
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consider isolating your journal receivers in user ASPs when you start journaling
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your indexes. Placing journal receivers in their own user ASP provides the
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best journal management performance, while helping to protect them from a
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disk failure.</p>
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</div>
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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="rbal1rcvjrn.htm" title="Journal management can be used as a part of the backup and recovery strategy for relational databases and indexes.">Journal management for distributed relational databases</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="../cl/strjrnap.htm">Start Journal Access Path (STRJRNAP) command</a></div>
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<div><a href="../cl/savobj.htm">Save Object (SAVOBJ) command</a></div>
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<div><a href="../cl/savlib.htm">Save Library (SAVLIB) command</a></div>
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</div>
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</div>
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</body>
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