Servers, Instances, and Databases

DB2 Universal Database sees the world as a hierarchy of objects. Workstations (or servers) on which DB2 UDB has been installed occupy the highest level of this hierarchy. During the installation process, program files for a background process known as the DB2 Database Manager are physically copied to a specific location on the server and an instance of the DB2 Database Manager is created. Instances occupy the second level in the hierarchy and are responsible for managing system resources and databases that fall under their control. Although only one instance is created initially, several instances can exist. Each instance behaves like a separate installation of DB2 UDB, even though all instances within a system share the same DB2 Database Manager program files (which were copied to the workstation during the installation process). And although multiple instances share the same binary code, each runs independently of the others and has its own environment (which can be modified by altering the contents of its associated configuration file).

Every instance controls access to one or more databases. Databases make up the third level in the hierarchy and are responsible for managing the storage, modification, and retrieval of data. Like instances, databases work independently of each other. Each database has its own environment (also controlled by a configuration file), as well as its own set of grantable authorities and privileges to govern how users interact with the data and database objects it controls. Figure 4-1 shows the hierarchical relationship between systems, instances, and databases.

Figure 4-1. Hierarchical relationship between systems, instances, and databases.