Catalogs allow you to implement multiple logical databases for synchronization. If your local physical database has replica data from multiple master databases, then the replica database needs one catalog for each master database. Note that a catalog on a replica database can contain not only synchronized data, but also local data, which belongs to the local database only and never gets replicated to or from other databases.
In this way, tables are defined in both replica and master databases to distinguish local data from shared data. Shared data is synchronized with the master database, but data belonging to only the replica database or to only the master database is never changed during synchronization.
In a multi-master environment, catalogs keep data from different master databases separated. Object name conflicts between catalogs do not occur. Even when the same table names and other object names are used in different master databases, the distinct catalog names for each master database qualify table and object names, as well as provide a way to specify which objects belong to which master database. In addition, solidDB Advanced Replication enforces that a single catalog does not contain objects from different master databases.
Schema names in master and replica catalogs must be identical. This is consistent with the basic two-tiered architecture, which is no different from a single replica that is registered to a single master. When a database is created, a default schema name is created which is the user id of the database owner. Separate schemas within databases are created with the CREATE SCHEMA statement. For details on managing database objects with schemas, see Managing database objects.
The use of catalogs and schemas for synchronization in solidDB Advanced Replication offers a flexible and scalable architecture. One replica catalog is mapped to one master catalog. However, a single physical database can have multiple catalogs. Additional master databases are included by creating more master catalogs in the same local database which map to new replica catalogs in the same or different database servers. Furthermore, both master catalogs and replica catalogs can exist in the same physical database.
As shown in Advanced multi-tier architecture, a master/replica hierarchy can have more than two layers, and some catalogs within that hierarchy can serve as both replica and master catalogs. For details on defining catalogs with the dual role of master and replica, see Defining master and replica databases.