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217 lines
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217 lines
9.0 KiB
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Using Hot Failovers</title>
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Getting Started with Berkeley DB Transaction Processing" />
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<link rel="up" href="filemanagement.html" title="Chapter 5. Managing DB Files" />
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<link rel="prev" href="architectrecovery.html" title="Designing Your Application for Recovery" />
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<link rel="next" href="logfileremoval.html" title="Removing Log Files" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 12.1.6.2</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Using Hot Failovers</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="architectrecovery.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 5. Managing DB Files</th>
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<td width="20%" align="right"> <a accesskey="n" href="logfileremoval.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="hotfailover"></a>Using Hot Failovers</h2>
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</div>
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</div>
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</div>
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<p>
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You can maintain a backup that can be used for failover purposes.
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Hot failovers differ from the backup and restore
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procedures described previously in this chapter in that data
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used for traditional backups is typically copied to offline storage.
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Recovery time for a traditional backup is determined by:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p>
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How quickly you can retrieve that storage media.
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Typically storage media for critical backups is moved
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to a safe facility in a remote location, so this step can
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take a relatively long time.
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</p>
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</li>
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<li>
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<p>
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How fast you can read the backup from the storage media
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to a local disk drive. If you have very large backups,
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or if your storage media is very slow, this can be a
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lengthy process.
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</p>
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</li>
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<li>
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<p>
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How long it takes you to run catastrophic recovery
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against the newly restored backup. As described earlier
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in this chapter, this process can be lengthy because
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every log file must be examined during the recovery
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process.
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</p>
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</li>
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</ul>
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</div>
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<p>
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When you use a hot failover, the backup is maintained
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at a location that is reasonably fast to access. Usually, this
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is a second disk drive local to the machine.
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In this situation, recovery time is very quick
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because you only have to reopen your
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environment and database, using the failover environment
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for the environment open.
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</p>
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<p>
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Hot failovers obviously do not protect you from truly
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catastrophic disasters (such as a fire in your machine room)
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because the backup is still local to the machine. However,
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you can guard against more mundane problems (such as a broken
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disk drive) by keeping the backup on a
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second drive that is managed by an alternate disk controller.
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</p>
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<p>
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To maintain a hot failover:
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</p>
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<div class="orderedlist">
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<ol type="1">
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<li>
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<p>
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Copy all the active database files to the failover
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directory. Use the <span class="command"><strong>db_archive</strong></span>
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command line utility with the
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<code class="literal">-s</code> option to identify all the active
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database files.
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</p>
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</li>
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<li>
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<p>
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Identify all the inactive log files in your production
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environment and <span class="emphasis"><em>move</em></span> these to the failover
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directory. Use the <span class="command"><strong>db_archive</strong></span>
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command with no command line options to obtain a list
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of these log files.
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</p>
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</li>
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<li>
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<p>
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Identify the active log files in your production
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environment, and <span class="emphasis"><em>copy</em></span> these to the
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failover directory. Use the
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<span class="command"><strong>db_archive</strong></span> command with the
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<code class="literal">-l</code> option to obtain a list of these
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log files.
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</p>
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</li>
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<li>
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<p>
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Run catastrophic recovery against the failover
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directory. Use the <span class="command"><strong>db_recover</strong></span>
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command with the <code class="literal">-c</code> option to do
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this.
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</p>
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</li>
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<li>
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<p>
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Optionally copy the backup to an archival location.
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</p>
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</li>
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</ol>
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</div>
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<p>
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Once you have performed this procedure, you can maintain an
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active hot backup by repeating steps 2 - 5 as often
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as is required by your application.
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</p>
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<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
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<h3 class="title">Note</h3>
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<p>
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If you perform step 1, steps 2-5 must follow in order to
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ensure consistency of your hot backup.
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</p>
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</div>
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<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
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<h3 class="title">Note</h3>
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<p>
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Rather than use the previous procedure, you can use the
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<span class="command"><strong>db_hotbackup</strong></span> command line utility to do the
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same thing. This utility will (optionally) run a checkpoint and
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then copy all necessary files to a target directory for you.
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</p>
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</div>
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<p>
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To actually perform a failover, simply:
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</p>
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<div class="orderedlist">
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<ol type="1">
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<li>
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<p>
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Shut down all processes which are running against the original environment.
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</p>
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</li>
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<li>
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<p>
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If you have an archival copy of the backup environment,
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you can optionally try copying the remaining log files
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from the original environment and running catastrophic
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recovery against that backup environment. Do this
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<span class="emphasis"><em>only</em></span> if you have a an archival
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copy of the backup environment.
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</p>
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<p>
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This step can allow you to recover data created or
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modified in the original environment, but which did not
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have a chance to be reflected in the hot backup
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environment.
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</p>
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</li>
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<li>
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<p>
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Reopen your environment and databases as normal, but use
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the backup environment instead of the production
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environment.
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</p>
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</li>
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</ol>
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</div>
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</div>
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<div class="navfooter">
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<hr />
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<table width="100%" summary="Navigation footer">
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<tr>
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<td width="40%" align="left"><a accesskey="p" href="architectrecovery.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="filemanagement.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="logfileremoval.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">Designing Your Application for Recovery </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> Removing Log Files</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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