The synchronization architecture of a multi-database system requires a way for applications to download data from the master database to the replica database, and to refresh this replica data on an as-needed basis.
A publication is a definition of a set of master data that can be downloaded to replicas. Replica databases use subscriptions to register their interest in a particular publication from the master. A publication is registered in a replica. Users can refresh data from only those publications that are registered. In this way publication parameters are validated, preventing users from accidentally refreshing from unwanted or non-existing publications or making ad hoc refresh commands.
The initial download (refresh) always returns data of a full publication; all data of the publication that matches the search criteria (given as publication parameters) is sent to the replica database.
After the initial download, subsequent refreshes to the same publication (using the same parameter values) receive only the data that has been changed since the prior refresh. This is known as an incremental refresh. Typically, only publication updates with the latest modifications need to be sent to a replica. Creating publications and specifying that they be incremental are done through solidDB® advanced replication commands, which are extensions to solidDB® SQL.