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129 lines
6.7 KiB
HTML
129 lines
6.7 KiB
HTML
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<?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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<html xmlns="http://www.w3.org/1999/xhtml">
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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>Hot Standby</title>
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<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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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 Java Edition" />
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<link rel="up" href="backuprestore.html" title="Chapter 11. Backing up and Restoring Berkeley DB Java Edition Applications" />
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<link rel="prev" href="catastrophicrecovery.html" title="Performing Catastrophic Recovery" />
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<link rel="next" href="administration.html" title="Chapter 12. Administering Berkeley DB Java Edition Applications" />
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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 12.2.7.5</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">Hot Standby</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="catastrophicrecovery.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 11. Backing up and Restoring Berkeley DB Java Edition Applications</th>
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<td width="20%" align="right"> <a accesskey="n" href="administration.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>Hot Standby</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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As a final backup/recovery strategy, you can create a hot standby. Note that using hot standbys requires
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your application to be able to specify its environment home directory at application startup time. Most
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application developers allow the environment home directory to be identified using a command line option or a
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configuration or properties file. If your application has its
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environment home hard-coded into it, you cannot use hot standbys.
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</p>
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<p>
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You create a hot standby by periodically backing up your database to an alternative
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location on disk. Usually this alternative location is on a separate physical drive from
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where you normally keep your database, but if multiple drives are not available then you
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should at least put the hot standby on a separate disk partition.
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</p>
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<p>
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You failover to your hot standby by causing your application to reopen its environment using the hot standby
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location.
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</p>
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<p>
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Note that a hot standby should not be used as a substitute for backing up and archiving your data to a safe
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location away from your operating environment. Even if your data is spread across multiple physical disks, a
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truly serious catastrophe (fires, malevolent software viruses,
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faulty disk controllers, and so forth)
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can still cause you to lose your data.
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</p>
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<p>
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To create and maintain a hot standby:
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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 log files (<code class="filename">*.jdb</code>) from your environment
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directory to the location where you want to keep your standby. Either a hot
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or an offline backup can be used for this purpose, but typically a hot
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standby is initially created by taking an offline backup of your database.
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This ensures that you have captured the contents of your in-memory cache.
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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 are using subdirectories to store your log files, then you must backup
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the subdirectories, making sure to keep log files in the subdirectory in which
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JE placed them. For information on using subdirectories to store your log
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files, see <a class="xref" href="env.html#multisubdir" title="Multiple Environment Subdirectories">Multiple Environment Subdirectories</a>.
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</p>
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</div>
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</li>
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<li>
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<p>
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Periodically copy to your standby directory any log files that were changed or created since the
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time of your last copy. Most backup software is capable of performing this kind of an incremental
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backup for you.
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</p>
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<p>
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Note that the frequency of your incremental copies determines the amount of data that is at risk due to catastrophic
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failures. For example, if you perform the incremental copy once an hour then at most your hot standby is an hour behind
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your production database, and so you are risking at most an hours worth of database changes.
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</p>
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</li>
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<li>
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<p>
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Remove any <code class="filename">*.jdb</code> files from the hot standby directory that have been removed or
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renamed to <code class="filename">.del</code> files in the primary directory. This is not necessary for
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consistency, but will help to reduce disk space consumed by the hot standby.
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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="catastrophicrecovery.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="backuprestore.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="administration.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">Performing Catastrophic 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"> Chapter 12. Administering Berkeley DB Java Edition Applications</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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