132 lines
9.8 KiB
HTML
132 lines
9.8 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="copyright" content="(C) Copyright IBM Corporation 2005" />
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Share files" />
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<meta name="abstract" content="File management on iSeries provides several levels of support for shared files. Files can be shared among many users, many jobs, or many programs within the same job." />
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<meta name="description" content="File management on iSeries provides several levels of support for shared files. Files can be shared among many users, many jobs, or many programs within the same job." />
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<meta name="DC.subject" content="SHARE parameter, description, sharing file, in same job, general considerations, file, sharing, open considerations, sharing files in same job, parameter, run-time, shared files in same job, original program model, SHARE, open operation, sharing files, close operation, scope in ILE model, ILE (Integrated Language Environment) model, Integrated Language Environment (ILE) model, high-level language, activation group, definition, open data path (ODP), ODP (open data path)" />
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<meta name="keywords" content="SHARE parameter, description, sharing file, in same job, general considerations, file, sharing, open considerations, sharing files in same job, parameter, run-time, shared files in same job, original program model, SHARE, open operation, sharing files, close operation, scope in ILE model, ILE (Integrated Language Environment) model, Integrated Language Environment (ILE) model, high-level language, activation group, definition, open data path (ODP), ODP (open data path)" />
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<meta name="DC.Relation" scheme="URI" content="rbal3openc.htm" />
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<meta name="DC.Relation" scheme="URI" content="rbal3closec.htm" />
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<meta name="DC.Relation" scheme="URI" content="rbal3ft.htm" />
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<meta name="DC.Identifier" content="rbal3share" />
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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>Share files</title>
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</head>
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<body id="rbal3share"><a name="rbal3share"><!-- --></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">Share files</h1>
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<div><p>File management on <span class="keyword">iSeries™</span> provides
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several levels of support for shared files. Files can be shared among many
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users, many jobs, or many programs within the same job.</p>
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<p> The server automatically provides the first level of support.
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By default, the server lets multiple users and multiple jobs use one file
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at the same time. The server allocates the file and its associated resources
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for each use of the file in such a way that it can prevent conflicting uses.
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Within the same job, programs can share files if one program opens the same
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file more than once or if different programs open the same file. Even though
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the same file is being used, each open operation creates a new path from the
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program to the data or device, so that each open represents an independent
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use of the file.</p>
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<div class="section"><h4 class="sectiontitle">Open data path</h4><div class="p">A closer level of sharing within
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a job allows more than one program to share the same path to the data or device.
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This path, called an <strong>open data path</strong>, is the path through which all
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of the read and write operations for the file are performed. You can use this
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level of sharing by specifying the SHARE parameter on the create file, change
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file, and override file commands. The SHARE parameter allows more than one
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program to share the file status, positions, and storage area. It can improve
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performance by reducing the amount of main storage the job needs and by reducing
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the time it takes to open and close the file. <span class="keyword">iSeries</span> bases
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this level of sharing on two models: <ul><li>The <strong>original program model</strong> is the set of functions for compiling
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source code and creating high-level language programs on the <span class="keyword">iSeries</span> server
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before the Integrated
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Language Environment<sup>®</sup> (ILE) model was introduced.</li>
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<li>The <strong>ILE model</strong> is the set of constructs and interfaces that provide
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a common run-time environment and run-time bindable application programming
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interface (APIs) for all ILE-conforming high-level languages.</li>
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</ul>
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</div>
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</div>
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<div class="section"><h4 class="sectiontitle">Shared files in the original program model</h4><p>In the
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original program model, the SHARE(*YES) parameter lets two or more programs
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that run in the same job share an open data path (ODP). It connects the program
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to a file. If not specified otherwise, every time a file is opened a new open
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data path is built. You can specify that if a file is opened more than once
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and an open data path is still active for it in the same job, the active ODP
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for the file can be used with the current open of the file; a new open data
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path does not need to be created. This reduces the amount of time that is
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required to open the file after the first opened to open the file after the
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first open, and the amount of main storage that is required by the job. You
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must specify SHARE(*YES) for the first open and other opens of the same file
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to share the open data path. A well-designed (for performance) application
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will normally do a shared open on database files that multiple programs will
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open in the same job. Specifying SHARE(*YES) for other files depends on the
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application.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Shared files in the ILE model</h4><p>In the ILE model,
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shared files are scoped either to the job level or to the activation group
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level. An <strong>activation group</strong> is a substructure of a run-time job. It
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consists of server resources (storage for program or procedure variables,
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commitment definitions, and open files) that are allocated to one or more
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programs. An activation group is like a miniature job within a job.</p>
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<p>Any
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programs that run in any activation group can share shared files that are
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scoped to the job level. Only programs that run in the same activation group
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can share shared files that are scoped to the activation group level.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Share files: Considerations</h4><p>Sharing
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files allows you to have programs within a job interact in ways that would
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otherwise not be possible. However, you need to understand the effects of
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opening, performing read and write operations, and closing shared files.</p>
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<p>You
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should also see the appropriate documentation for all of the file types to
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understand how this support works, and the rules your programs must follow
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to use it correctly.</p>
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<div class="note"><span class="notetitle">Note:</span> Most high-level language programs process an
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open or a close operation independent of whether the file is being shared.
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You do not specify that the file is being shared in the high-level language
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program. You indicate that the file is being shared in the same job through
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the SHARE parameter. You specify the SHARE parameter only on the CREATE, CHANGE,
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and OVERRIDE file commands. Refer to your appropriate language information
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for more information.</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="rbal3openc.htm">Open considerations for files shared in a job</a></strong><br />
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There are certain points to consider when you open a shared file in the same job by specifying SHARE(*YES).</li>
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<li class="ulchildlink"><strong><a href="rbal3ioc.htm">I/O considerations for files shared in a job</a></strong><br />
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The server uses the same input/output area for all programs sharing the file, so the order of the operations is sequential regardless of which program does the operation.</li>
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<li class="ulchildlink"><strong><a href="rbal3closec.htm">Close considerations for files shared in a job</a></strong><br />
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The processing done when a program closes a shared file depends on whether other programs currently share the open data path.</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="rbal3workwith.htm" title="This topic describes the various tasks that can be used to ensure that files are used effectively.">Work with database files</a></div>
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</div>
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<div class="relconcepts"><strong>Related concepts</strong><br />
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<div><a href="rbal3ft.htm">File types</a></div>
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<div><a href="rbal3openiofba.htm" title="The server monitors the status of a file in feedback areas once it has successfully opened the file. As the server performs operations on a file, it updates the feedback areas to reflect the latest status. These feedback areas give you greater control over applications and provide important information when errors occur.">Monitor file status with the open and I/O feedback area</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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