A database instance is defined as the master instance. The table contents of the master instance are then copied to one or several client instances. Once this has been done, all changes made to the tables involved are synchronized between the master instance and the client instances. For this purpose, the database contents are grouped into logical units (replication units) whose properties can be configured independently of each other. For example, filter criteria, tables, column name translations, and type conversions can be defined for each unit.
A database instance that wants to transfer data
reports to the message server in order to receive the current data changes
stored there. At the same time, the database instance transfers
its own data changes, and these are retained by the message server until all
of the database instances involved have been fetched.
Change collisions (i.e. if sites taking part in the
synchronization want to transfer conflicting changes to each other) are
resolved by the Synchronization Service using version numbers or before
images.
Synchronization process