70 lines
4.7 KiB
HTML
70 lines
4.7 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 name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Input/output considerations for files shared in a job or activation group" />
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<meta name="abstract" content="Listed here are the considerations for processing a database file that is shared in the same job or activation group." />
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<meta name="description" content="Listed here are the considerations for processing a database file that is shared in the same job or activation group." />
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<meta name="DC.subject" content="input/output, sharing files in a job, sharing files in an activation group, database file, sharing in a job, input/output considerations, sharing in an activation group" />
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<meta name="keywords" content="input/output, sharing files in a job, sharing files in an activation group, database file, sharing in a job, input/output considerations, sharing in an activation group" />
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<meta name="DC.Relation" scheme="URI" content="rbafosfile.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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<title>Input/output considerations for files shared in a job or activation
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group</title>
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</head>
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<body id="rbafoiocon"><a name="rbafoiocon"><!-- --></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 files shared in a job or activation
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group</h1>
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<div><p>Listed here are the considerations for processing a database file
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that is shared in the same job or activation group.</p>
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<div class="p"><ul><li>Because only one open data path is allowed for a shared file, only one
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record position is maintained for all the programs in the job or activation
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group that is sharing the file. If a program establishes a position for a
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record using a read or a read-for-update operation, and then calls another
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program that also uses the shared file, the record position might have moved
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or a record lock been released when the called program returns to the calling
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program. This can cause errors in the calling program because of an unexpected
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record position or lock condition. When sharing files, it is your responsibility
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to manage the record position and record locking considerations by re-establishing
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position and locks.</li>
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<li>If a shared file is first opened for update operation, this does not necessarily
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cause every subsequent program that shares the file to request a record lock.
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The system determines the type of record lock needed for each program using
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the file. The system tries to keep lock contention to a minimum, while still
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ensuring data integrity. <p>For example, PGMA is the first program in the
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job or activation group to open a shared file. PGMA intends to update records
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in the file; therefore, when the program reads a record for update operation,
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it locks the record. PGMA then calls PGMB. PGMB also uses the shared file,
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but it does not update any records in the file; PGMB just reads records. Even
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though PGMA originally opened the shared file as update-capable, PGMB does
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not lock the records it reads, because of the processing specifications in
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PGMB. Thus, the system ensures data integrity, while minimizing record lock
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contention.</p>
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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="rbafosfile.htm" title="By default, the database management system lets one file be read and changed by many users at the same time. However, you can share the database files in the same job or activation group through the SHARE parameter.">Share database files in the same job or activation group</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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