87 lines
7.4 KiB
HTML
87 lines
7.4 KiB
HTML
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<meta name="abstract" content="If your program processes a database file sequentially for input only or output only, you might be able to improve performance using the sequential-only processing (SEQONLY) parameter on the Override with Database File (OVRDBF) or the Open Database File (OPNDBF) command." />
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<title>Sequential-only processing of database files</title>
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</head>
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<body id="rbafoseqop"><a name="rbafoseqop"><!-- --></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">Sequential-only processing of database files</h1>
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<div><p> If your program processes a database file sequentially for input
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only or output only, you might be able to improve performance using the sequential-only
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processing (SEQONLY) parameter on the Override with Database File (OVRDBF)
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or the Open Database File (OPNDBF) command.</p>
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<div class="p">To use SEQONLY processing, the file must be opened for input-only or output-only.
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The NBRRCDS parameter can be used with any combination of open options. (The
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Open Query File (OPNQRYF) command uses sequential-only processing whenever
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possible.) Depending on your high-level language specifications, the high-level
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language can also use sequential-only processing as the default. For example,
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if you open a file for input only and the only file operations specified in
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the high-level language program are sequential read operations, then the high-level
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language automatically requests sequential-only processing. <div class="note"><span class="notetitle">Note:</span> File positioning
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operations are not considered sequential read operations; therefore, a high-level
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language program containing positioning operations will <em>not</em> automatically
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request sequential-only processing. (The SETLL operation in the RPG/400<sup>®</sup> language
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and the START operation in the COBOL/400<sup>®</sup> language are examples of
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file positioning operations.) Even though the high-level language program
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cannot automatically request sequential-only processing, you can request it
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using the SEQONLY parameter on the Override with Database File (OVRDBF) command.</div>
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</div>
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<p>If you specify sequential-only processing, you can also specify the number
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of records to be moved as one unit between the system database main storage
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area and the job's internal data main storage area. If you do not specify
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the sequential-only number of records to be moved, the system calculates a
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number based on the number of records that fit into a 4096-byte buffer.</p>
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<div class="p">The system also provides you a way to control the number of records that
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are moved as a unit between auxiliary storage and main storage. If you are
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reading the data in the file in the same order as the data is physically stored,
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you can improve the performance of your job using the NBRRCDS parameter on
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the OVRDBF command. <div class="note"><span class="notetitle">Note:</span> Sequential-only processing should not be used with
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a keyed sequence access path file unless the physical data is in the same
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order as the access path. SEQONLY(*YES) processing might cause poor application
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performance until the physical data is reorganized into the access path's
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order.</div>
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</div>
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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="rbafoocons.htm">Open considerations for sequential-only processing</a></strong><br />
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The considerations apply for opening files when sequential-only processing is specified. If the system determines that sequential-only processing is not allowed, a message is sent to the program to indicate that the request for sequential-only processing is not being accepted; however, the file is still opened for processing.</li>
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<li class="ulchildlink"><strong><a href="rbafoicons.htm">Input/output considerations for sequential-only processing</a></strong><br />
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The considerations apply for input/output operations on files when sequential-only processing is specified.</li>
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<li class="ulchildlink"><strong><a href="rbafoclosc.htm">Close considerations for sequential-only processing</a></strong><br />
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The considerations apply for closing files when sequential-only processing is specified.</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="rbafopreopn.htm" title="These topics describe the file processing parameters and other methods or considerations that can affect database file processing.">Database file processing: Runtime considerations</a></div>
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