105 lines
6.4 KiB
HTML
105 lines
6.4 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="task" />
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<meta name="DC.Title" content="Minimize locks" />
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<meta name="abstract" content="A typical way to minimize record locks is to release the record lock. (This technique does not work if LCKLVL(*ALL) has been specified.)" />
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<meta name="description" content="A typical way to minimize record locks is to release the record lock. (This technique does not work if LCKLVL(*ALL) has been specified.)" />
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<meta name="DC.Relation" scheme="URI" content="rzakjdeadlocks.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 2004, 2006" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Identifier" content="rzakjminimizelock" />
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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>Minimize locks</title>
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</head>
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<body id="rzakjminimizelock"><a name="rzakjminimizelock"><!-- --></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">Minimize locks</h1>
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<div><p>A typical way to minimize record locks is to release the record
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lock. (This technique does not work if LCKLVL(*ALL) has been specified.)</p>
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<div class="section"><p>Here is an example of minimize record by releasing
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the record lock. A single file maintenance application typically follows these
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steps:</p>
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<ol><li>Display a prompt for a record identification to be changed.</li>
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<li>Retrieve the requested record.</li>
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<li>Display the record.</li>
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<li>Allow the workstation user to make the change.</li>
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<li>Update the record.</li>
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</ol>
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<p>In most cases, the record is locked from the access of the requested
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record through the update. The record wait time might be exceeded for another
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job that is waiting for the record. To avoid locking a record while the workstation
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user is considering a change, release the record after it is retrieved from
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the database (before the record display appears). You then need to access
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the record again before updating. If the record was changed between the time
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it was released and the time it was accessed again, you must inform the workstation
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user. The program can determine if the record was changed by saving one or
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more fields of the original record and comparing them to the fields in the
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same record after it is retrieved as follows:</p>
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<ul><li>Use an update count field in the record and add 1 to the field just before
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an update. The program saves the original value and compares it to the value
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in the field when the record is retrieved again. If a change has occurred,
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the workstation user is informed and the record appears again. The update
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count field is changed only if an update occurs. The record is released while
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the workstation user is considering a change. If you use this technique, you
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must use it in every program that updates the file.</li>
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<li>Save the contents of the entire data record and compare it to the record
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the next time it is retrieved.</li>
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</ul>
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<p>In both cases above, the sequence of operations prevents the simple
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use of externally described data in RPG where the same field names are used
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in the master record and in the display file. Using the same field names (in
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RPG) does not work because the workstation user's changes are overlaid when
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the record is retrieved again.You can solve this problem by moving the record
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data to a data structure. Or, if you use the DDS keyword <span class="keyword">RTNDTA</span>,
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you can continue to use externally described data. The <span class="keyword">RTNDTA</span> keyword
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allows your program to reread data on the display without the operating system
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having to move data from the display to the program. This allows the program
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to do as follows:</p>
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</div>
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<ol><li><span>Prompt for the record identification.</span></li>
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<li><span>Retrieve the requested record from the database.</span></li>
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<li><span>Release the record.</span></li>
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<li><span>Save the field or fields used to determine if the record was changed.</span></li>
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<li><span>Display the record and wait for the workstation user to respond.</span></li>
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</ol>
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<div class="section"><p>If the workstation user changes the record on the display, the
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program uses the following sequence:</p>
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<ol><li>Retrieve the record from the database again.</li>
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<li>Compare the saved fields to determine if the database record has been
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changed. If it has been changed, the program releases the record and sends
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a message when the record appears.</li>
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<li>Retrieve the record from the display by running a read operation with
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the <span class="keyword">RTNDTA</span> keyword and updates the record in the database
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record.</li>
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<li>Proceed to the next logical prompt because there are no additional
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records to be released if the workstation user cancels the request.</li>
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</ol>
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<p>LCKLVL(*CHG) and LCKLVL(*CS) work in this situation. If LCKLVL(*ALL)
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is used, you must release the record lock by using a commit or rollback operation.</p>
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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="rzakjoptimize.htm" title="Using commitment control requires resources that can affect system performance. Several factors affect system performance regarding commitment control.">Optimize performance for commitment control</a></div>
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</div>
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<div class="reltasks"><strong>Related tasks</strong><br />
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<div><a href="rzakjdeadlocks.htm" title="Find deadlock conditions by using these instructions.">Detect deadlocks</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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