CONTINUOUS AVAILABILITY AND EFFICIENT BACKUP FOR EXTERNALLY REFERENCED OBJECTS

A computing system provides continuous availability of data files that are maintained at a file management system and linked to a database management system (DBMS) through a Datalink data type, even while any particular file is being changed with DBMS append or update operations. When a file is linked, it is designated to be available for read-only operations. A user who wants to perform updates on a file gets a "check-out" copy of the file for updating operations, such that the original file remains linked to the database system while the copy is being updated and remains available to other users. The file management system includes a "check-in" function that receives the updated file, saves the updated file under a new name different from the original, updates the Datalink, generates new metadata for the updated file, and transactionally updates the file with its new metadata. In this way, data files are continuously available to all users through appending and updating actions. Since updating Datalinks requires the file management system to initiate backup, a "delta versioning" operation, which reduces the data needed to support backup operations, permits more efficient backup of data files and enables the continuously available files to be backed up and consistent.