<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html lang="en-us" xml:lang="en-us"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <meta name="security" content="public" /> <meta name="Robots" content="index,follow" /> <meta http-equiv="PICS-Label" content='(PICS-1.1 "http://www.icra.org/ratingsv02.html" l gen true r (cz 1 lz 1 nz 1 oz 1 vz 1) "http://www.rsac.org/ratingsv01.html" l gen true r (n 0 s 0 v 0 l 0) "http://www.classify.org/safesurf/" l gen true r (SS~~000 1))' /> <meta name="DC.Type" content="concept" /> <meta name="DC.Title" content="Restart highly available cluster applications" /> <meta name="abstract" content="To restart an application, the application needs to know its state at the time of the failover or switchover." /> <meta name="description" content="To restart an application, the application needs to know its state at the time of the failover or switchover." /> <meta name="DC.Relation" scheme="URI" content="rzaigapplicationswritehighlyavailable.htm" /> <meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" /> <meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1998, 2006" /> <meta name="DC.Format" content="XHTML" /> <meta name="DC.Identifier" content="rzaigapplicationsrestart" /> <meta name="DC.Language" content="en-us" /> <!-- All rights reserved. Licensed Materials Property of IBM --> <!-- US Government Users Restricted Rights --> <!-- Use, duplication or disclosure restricted by --> <!-- GSA ADP Schedule Contract with IBM Corp. --> <link rel="stylesheet" type="text/css" href="./ibmdita.css" /> <link rel="stylesheet" type="text/css" href="./ic.css" /> <title>Restart highly available cluster applications</title> </head> <body id="rzaigapplicationsrestart"><a name="rzaigapplicationsrestart"><!-- --></a> <!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script> <h1 class="topictitle1">Restart highly available cluster applications</h1> <div><p>To restart an application, the application needs to know its state at the time of the failover or switchover.</p> <p>State information is application specific; therefore, the application must determine what information is needed. Without any state information, the application can be restarted on your PC. However, you will must reestablish your position within the application.</p> <p>Several methods are available to save application state information for the backup system. Each application needs to determine which method works best for it.</p> <ul><li>The application can transfer all state information to the requesting client system. When a switchover or failover occurs, the application uses the stored state on the client to reestablish the state in the new server. This can be accomplished by using the Distribute Information API or Clustered Hash Table APIs.</li> <li>The application can replicate state information (such as job information and other control structures that are associated with the application) on a real-time basis. For every change in the structures, the application ships the change over to the backup system.</li> <li>The application can store pertinent state information that is associated with its application in the exit program data portion of the cluster resource group for that application. This method assumes that a small amount of state information is required. You can use the <span class="apiname">Change Cluster Resource Group (QcstChangeClusterResourceGroup)</span> API to do this.</li> <li>The application can store state information in a data object that is being replicated to the backup systems along with the application's data.</li> <li>The application can store state information in a data object contained in the switchable IASP that also contains the application's data.</li> <li>The application can store the state information about the client.</li> <li>No state information is saved, and you need to perform the recovery.</li> </ul> <div class="note"><span class="notetitle">Note:</span> The amount of information that is required to be saved is lessened if the application uses some form of checkpoint-restart processing. State information is only saved at predetermined application checkpoints. Restart then takes you back to the last known checkpoint which is similar to how database's commitment control processing works.</div> </div> <div> <div class="familylinks"> <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> </div> </div> </body> </html>