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Hot Standby
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## Hot Standby

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.

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.

You failover to your hot standby by causing your application to reopen its environment using the hot standby location.

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.

To create and maintain a hot standby:

1. Copy all log files (`*.jdb`) 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.

   ### Note

   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 Multiple Environment Subdirectories.

2. 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.

   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.

3. Remove any `*.jdb` files from the hot standby directory that have been removed or renamed to `.del` 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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