Setting the delta file

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Setting the delta file

By default, the delta file lives in the same directory as the database itself. The file name is also the same, but with .delta appended. This is usually not a problem, but sometimes it is desirable or even necessary to change the location, e.g. when the database is stored on a raw device. nbackup itself has no provision for setting the location; this must be done through SQL.

Make a connection to the database with any client that allows you to enter your own SQL statements and give the command:

 alter database add difference file 'path-and-filename'

The custom delta file specification is persistent in the database; it is stored in the system table RDB$FILES. To revert to the default behaviour, issue the following statement:

 alter database drop difference file

You can also specify a custom delta location while creating a new database:

 create database 'path-and-dbname' difference file 'path-and-deltaname'


  • If you specify a bare file name with [ADD] DIFFERENCE FILE, the delta will likely not be created in the same directory as the database, but in the current directory as seen from the server. On Windows this may e.g. be the system directory. The same logic applies to relative paths.
  • The entire directory path must already exist. Firebird doesn't attempt to create any missing directories.
  • If you want to change your custom delta specification, you must first DROP the old one and then ADD the new one.

See also:
InterBase® and Firebird command-line utilities: nbackup

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