109 lines
7.9 KiB
HTML
109 lines
7.9 KiB
HTML
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<meta name="DC.Title" content="Example: Use a notify object to start an application" />
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<meta name="abstract" content="When a program is started after an abnormal end, it can look for an entry in the notify object. If the entry exists, the program can start a transaction again. After the transaction has been started again, the notify object is cleared by the program to prevent it from starting the same transaction yet another time." />
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<meta name="description" content="When a program is started after an abnormal end, it can look for an entry in the notify object. If the entry exists, the program can start a transaction again. After the transaction has been started again, the notify object is cleared by the program to prevent it from starting the same transaction yet another time." />
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<meta name="copyright" content="(C) Copyright IBM Corporation 2004, 2006" />
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<title>Example: Use a notify object to start an application</title>
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<body id="rzakjusenotify"><a name="rzakjusenotify"><!-- --></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">Example: Use a notify object to start an application</h1>
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<div><p>When a program is started after an abnormal end, it can look for
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an entry in the notify object. If the entry exists, the program can start
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a transaction again. After the transaction has been started again, the notify
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object is cleared by the program to prevent it from starting the same transaction
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yet another time.</p>
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<p>Here are ways to use a notify object:</p>
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<ul><li>If the commit identification is placed in a database file, query this
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file to determine where to start each application or workstation job again.</li>
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<li>If the commit identification is placed in a message queue for a particular
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workstation, a message can be sent to the work station users when they sign
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on to inform them of the last transaction committed.</li>
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<li>If the commit identification is placed in a database file that has a key
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or user name, the program can read this file when it is started. If a record
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exists in the file, start the program again. The program can send a message
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to the workstation user identifying the last transaction committed. Any recovery
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is performed by the program. If a record existed in the database file, the
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program deletes that record at the end of the program.</li>
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<li>For a batch application, the commit identification can be placed in a
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data area that contains totals, switch settings, and other status information
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necessary to start the application again. When the application is started,
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it accesses the data area and verifies the values stored there. If the application
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ends normally, the data area is set up for the next run.</li>
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<li>For a batch application, the commit identification can be sent to a message
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queue. A program that is run when the application is started can retrieve
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the messages from the queue and start the programs again.</li>
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</ul>
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<p>You can use several techniques for starting your applications
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again, depending on your application needs. In choosing the technique, consider
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the following information:</p>
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<ul><li>When there are multiple users of a program at the same time, a single
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data area cannot be used as the notify object because after an abnormal system
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end, the commit identification for each user will overlay each other in the
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data area.</li>
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<li>Your design for deleting information in the notify object must handle
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the situation when a failure occurs immediately following use
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of the information: <ul><li>If information is deleted immediately, it does not exist if another failure
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occurs before processing the interrupted transaction.</li>
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<li>The information in the notify object must not be deleted until the successful
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processing of the interrupted transaction. In this case, more than one entry
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will exist in the notify object if it is a database file or message queue.</li>
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<li>The program must access the last record if there is more than one entry.</li>
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</ul>
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</li>
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<li>A notify object cannot be used to provide the work station user with the
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last transaction committed because the notify object is updated only if a
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system or job failure occurs or if uncommitted changes exist at the normal
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end of a job.</li>
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<li>If information is displayed to the workstation user, it must be meaningful.
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This might require that the program translate codes kept in the notify object
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into information that will help the user start again.</li>
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<li>Information for starting again must be displayed if the work station user
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needs it. Additional logic in the program is required to prevent information
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from being displayed again when it is no longer meaningful.</li>
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<li>A single notify object and a standard processing program can provide a
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starting again function if the notify object is a database file. This standard
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processing program is called by the programs that require the ability to start
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again to minimize the changes to each individual program.</li>
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</ul>
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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="rzakjnotifyeach.htm">Example: Unique notify object for each program</a></strong><br />
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Using a single, unique notify object for each job allows use of an externally described commit identification even though there might be multiple users of the same program.</li>
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<li class="ulchildlink"><strong><a href="rzakjnotifyall.htm">Example: Single notify object for all programs</a></strong><br />
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Using a single notify object for all programs is advantageous because all information required to start again is in the same object and a standard approach to the notify object can be used in all programs. In this situation, use a unique combination of user and program identifications to make sure that the program accesses the correct information when it starts again.</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="rzakjscenario.htm" title="You can read scenarios and examples in this topic to see how one company sets up commitment control. Read code examples for programs that use commitment control.">Scenarios and examples: Commitment control</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="rzakjnotify.htm" title="A notify object is a message queue, data area, or database file that contains information identifying the last successful transaction completed for a particular commitment definition if that commitment definition did not end normally.">Commit notify object</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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