Apache NiFi Registry System Administrator's Guide
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Metadata Database

If using H2, the database file should be backed up periodically to an external location. In order to ensure a proper backup, NiFi Registry should be stopped to ensure no write operations are occurring while copying the file.

If using Postgres, backups may be taken on the Postgres database, or Postgres may be configured for high availability such that there is a failover or backup instance.

If starting a brand new NiFi Registry instance, the metadata database can be automatically rebuilt from the information in the GitFlowPersistenceProvider. This is a one-time operation during the first start of the application, and is not meant to keep the DB in sync with external changes made in Git. This feature only applies to flows and would not be able to restore information about extension bundles.