今天抽空了解了下 Oracle12C 的新特性之一： CDB 与 PDB，Oracle 12C 开始引入多租户的概念，允许 CDB(数据库容器)上支持多个 PDB(可挺拔数据库)，结构如下：
Components of a CDB
A CDB includes the following components:
The root, named
CDB$ROOT, stores Oracle-supplied metadata and common users. An example of metadata is the source code for Oracle-supplied PL/SQL packages. A common user is a database user known in every container. A CDB has exactly one root.
The seed, named
PDB$SEED, is a template that you can use to create new PDBs. You cannot add objects to or modify objects in the seed. A CDB has exactly one seed.
A PDB appears to users and applications as if it were a non-CDB. For example, a PDB can contain the data and code required to support a specific application. A PDB is fully backward compatible with Oracle Database releases before Oracle Database 12c.