89 lines
5.8 KiB
HTML
89 lines
5.8 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="DC.Type" content="concept" />
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<meta name="DC.Title" content="Input/output considerations for sequential-only processing" />
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<meta name="abstract" content="The considerations apply for input/output operations on files when sequential-only processing is specified." />
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<meta name="description" content="The considerations apply for input/output operations on files when sequential-only processing is specified." />
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<meta name="DC.subject" content="input/output, sequential-only processing, input/output considerations" />
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<meta name="keywords" content="input/output, sequential-only processing, input/output considerations" />
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<meta name="DC.Relation" scheme="URI" content="rbafoseqop.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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<!-- All rights reserved. Licensed Materials Property of IBM -->
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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>Input/output considerations for sequential-only processing</title>
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</head>
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<body id="rbafoicons"><a name="rbafoicons"><!-- --></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">Input/output considerations for sequential-only processing</h1>
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<div><p>The considerations apply for input/output operations on files when
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sequential-only processing is specified. </p>
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<div class="p"> <ul><li>For input, your program receives one record at a time from the input buffer.
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When all records in the input buffer are processed, the system automatically
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reads the next set of records. <div class="note"><span class="notetitle">Note:</span> Changes made after records are read into
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the input buffer are not reflected in the input buffer.</div>
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</li>
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<li>For output, your program must move one record at a time to the output
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buffer. When the output buffer is full, the system automatically adds the
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records to the database. <div class="note"><span class="notetitle">Note:</span> If you are using a journal, the entire buffer
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is written to the journal at one time as if the entries had logically occurred
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together. This journal processing occurs before the records are added to the
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database.</div>
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<p>If you use sequential-only processing for output, you might
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not see all the changes made to the file as they occur. For example, if sequential-only
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is specified for a file being used by PGMA, and PGMA is adding new records
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to the file and the SEQONLY parameter was specified with 5 as the number of
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records in the buffer, then only when the buffer is filled will the newly
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added records be transferred to the database. In this example, only when the
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fifth record was added, would the first five records be transferred to the
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database, and be available for processing by other jobs in the system.</p>
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<p>In
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addition, if you use sequential-only processing for output, some additions
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might not be made to the database if you do not handle the errors that can
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occur when records are moved from the buffer to the database. For example,
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assume that the buffer holds five records, and the third record in the buffer
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had a key that was a duplicate of another record in the file and the file
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was defined as a unique-key file. In this case, when the system transfers
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the buffer to the database it would add the first two records and then get
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a duplicate key error for the third. Because of this error, the third, fourth,
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and fifth records in the buffer would <em>not</em> be added to the database.</p>
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</li>
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<li>The force-end-of-data function can be used for output operations to force
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all records in the buffer to the database (except those records that would
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cause a duplicate key in a file defined as having unique keys, as described
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previously). The force-end-of-data function is only available in certain high-level
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languages.</li>
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<li>The number of records in a block will be changed to one if all of the
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following conditions are true: <ul><li>The member was opened for output-only processing or sequential-only processing.</li>
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<li>No override operations are in effect that have specified sequential-only
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processing.</li>
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<li>The file being opened is being extended because the increment number of
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records was set to zero.</li>
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<li>The number of bytes available in the file is less than the number of bytes
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that fit into a block of records.</li>
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</ul>
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</li>
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</ul>
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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="rbafoseqop.htm" title="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.">Sequential-only processing of database files</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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