Importance of Journal Restore

Importance of Journal Restore

A restorable backup of an InterSystems IRIS® database alone is not enough to provide a viable restore of production data. In the event of a failure that requires restoring from backup, you must also apply journal files (described in Journaling) to the restored copy of the database. This journal restore accomplishes the following:

• Restores all journaled updates from the time of the backup to the time of the failure.

• Restore the transactional integrity of the database by rolling back uncommitted transactions.

While the backup approaches described in this topic can provide you with a physically consistent copy of databases that can be individually restored, you must also do a journal restore, even if you have no journals newer than the time of the backup, to ensure that any transactions that were open at the time of the backup are rolled back. This means that any backup approach you use must include each database’s journal files.

When restoring a crash-consistent snapshot image of your entire system (as in common in a virtualized environment), normal InterSystems IRIS startup recovery automatically ensures both physical integrity (including completion of interrupted writes) through the write image journal or WIJ (see Write Image Journaling), and logical integrity (including transaction rollback) through journaling. This means, however, that any such snapshot backup image of a database must include all components from a single moment in time, including the database, the instance’s installation directory, the WIJ, and the journal files, as well as any other external files associated with the database.

Be sure to see Journaling Best Practices for important information about ensuring journal availability for recovery. In particular, as explained in that section, in the interests of performance and recoverability, InterSystems recommends placing the primary and alternate journal directories on storage devices that are separate from the devices used by databases and the WIJ, as well as separate from each other.