Containers in a CDB

A container is either a PDB or the root container (also called the root). The root is a collection of schemas, schema objects, and nonschema objects to which all PDBs belong

Every CDB has the following containers:

• Exactly one root

The root stores Oracle-supplied metadata and common users. An example of metadata is the source code for Oracle-supplied PL/SQL packages . A common user is a database user known in every container . The root container is named CDB$ROOT.

• Exactly one seed PDB

The seed PDB is a system-supplied template that the CDB can use to create new PDBs. The seed PDB is named PDB$SEED. You cannot add or modify objects in PDB$SEED.

• Zero or more user-created PDBs

A PDB is a user-created entity that contains the data and code required for a specific set of features. For example, a PDB can support a specific application, such as a human resources or sales application. No PDBs exist at creation of the CDB. You add PDBs based on your business requirements.

The following graphic shows a CDB with four containers: the root, seed, and two PDBs. Each PDB has its own dedicated application, and is managed by its own PDB administrator. A common user exists across a CDB with a single identity. In this example, common user SYS can manage the root and every PDB. At the physical level, this CDB has a database instance and database files, just as a non-CDB does.