je/docs/GettingStartedGuide/hotfailover.html

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<p>Library Version 12.2.7.5</p>
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<th colspan="3" align="center">Hot Standby</th>
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<h2 class="title" style="clear: both"><a id="hotfailover"></a>Hot Standby</h2>
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<p>
As a final backup/recovery strategy, you can create a hot standby. Note that using hot standbys requires
your application to be able to specify its environment home directory at application startup time. Most
application developers allow the environment home directory to be identified using a command line option or a
configuration or properties file. If your application has its
environment home hard-coded into it, you cannot use hot standbys.
</p>
<p>
You create a hot standby by periodically backing up your database to an alternative
location on disk. Usually this alternative location is on a separate physical drive from
where you normally keep your database, but if multiple drives are not available then you
should at least put the hot standby on a separate disk partition.
</p>
<p>
You failover to your hot standby by causing your application to reopen its environment using the hot standby
location.
</p>
<p>
Note that a hot standby should not be used as a substitute for backing up and archiving your data to a safe
location away from your operating environment. Even if your data is spread across multiple physical disks, a
truly serious catastrophe (fires, malevolent software viruses,
faulty disk controllers, and so forth)
can still cause you to lose your data.
</p>
<p>
To create and maintain a hot standby:
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Copy all log files (<code class="filename">*.jdb</code>) from your environment
directory to the location where you want to keep your standby. Either a hot
or an offline backup can be used for this purpose, but typically a hot
standby is initially created by taking an offline backup of your database.
This ensures that you have captured the contents of your in-memory cache.
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<h3 class="title">Note</h3>
<p>
If you are using subdirectories to store your log files, then you must backup
the subdirectories, making sure to keep log files in the subdirectory in which
JE placed them. For information on using subdirectories to store your log
files, see <a class="xref" href="env.html#multisubdir" title="Multiple Environment Subdirectories">Multiple Environment Subdirectories</a>.
</p>
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Periodically copy to your standby directory any log files that were changed or created since the
time of your last copy. Most backup software is capable of performing this kind of an incremental
backup for you.
</p>
<p>
Note that the frequency of your incremental copies determines the amount of data that is at risk due to catastrophic
failures. For example, if you perform the incremental copy once an hour then at most your hot standby is an hour behind
your production database, and so you are risking at most an hours worth of database changes.
</p>
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<p>
Remove any <code class="filename">*.jdb</code> files from the hot standby directory that have been removed or
renamed to <code class="filename">.del</code> files in the primary directory. This is not necessary for
consistency, but will help to reduce disk space consumed by the hot standby.
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