73 lines
4.8 KiB
HTML
73 lines
4.8 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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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Restart highly available cluster applications" />
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<meta name="abstract" content="To restart an application, the application needs to know its state at the time of the failover or switchover." />
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<meta name="description" content="To restart an application, the application needs to know its state at the time of the failover or switchover." />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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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>Restart highly available cluster applications</title>
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</head>
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<body id="rzaigapplicationsrestart"><a name="rzaigapplicationsrestart"><!-- --></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">Restart highly available cluster applications</h1>
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<div><p>To restart an application, the application needs to know its state
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at the time of the failover or switchover.</p>
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<p>State information is application specific; therefore, the application must
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determine what information is needed. Without any state information, the application
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can be restarted on your PC. However, you will must reestablish your position
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within the application.</p>
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<p>Several methods are available to save application state information for
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the backup system. Each application needs to determine which method works
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best for it.</p>
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<ul><li>The application can transfer all state information to the requesting client
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system. When a switchover or failover occurs, the application uses the stored
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state on the client to reestablish the state in the new server. This can
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be accomplished by using the Distribute Information API or Clustered Hash
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Table APIs.</li>
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<li>The application can replicate state information (such as job information
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and other control structures that are associated with the application) on
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a real-time basis. For every change in the structures, the application ships
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the change over to the backup system.</li>
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<li>The application can store pertinent state information that is associated
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with its application in the exit program data portion of the cluster resource
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group for that application. This method assumes that a small amount of state
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information is required. You can use the <span class="apiname">Change Cluster Resource
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Group (QcstChangeClusterResourceGroup)</span> API to do this.</li>
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<li>The application can store state information in a data object that is being
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replicated to the backup systems along with the application's data.</li>
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<li>The application can store state information in a data object contained
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in the switchable IASP that also contains the application's data.</li>
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<li>The application can store the state information about the client.</li>
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<li>No state information is saved, and you need to perform the recovery.</li>
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</ul>
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<div class="note"><span class="notetitle">Note:</span> The amount of information that is required to be saved is lessened if
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the application uses some form of checkpoint-restart processing. State information
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is only saved at predetermined application checkpoints. Restart then takes
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you back to the last known checkpoint which is similar to how database's commitment
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control processing works.</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="rzaigapplicationswritehighlyavailable.htm" title="A highly available application is one that can be resilient to a system outage in a clustered environment.">Writing a highly available cluster application</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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