What Happens When Databases are Allocated

When a database is allocated to a location, there will be a delay before the database appears at the Satellite. This is because the mechanism used to make sure consistency is as follows:

When a database is allocated, it is immediately copied to the target location and to any intermediate locations that do not already have it. When the database arrives, the target location sends a message back to the Hub, which updates the Global database by adding the database to the database lists for the locations involved. The Global database is then sent to the target location: when it arrives, the database is available for use.

When a database is de-allocated, it is removed from the allocation list of the location and its descendants in the Global database. The Global database is then sent to the location. When it arrives, the database is deleted (when there are no readers) and all reference to it is automatically removed from any MDBs in the System database. The Global database is also sent to any descendants of the location, which removes references to the database at the descendant locations.