Databases Reference
In-Depth Information
Chapter 23
Pluggable Databases
New with Oracle Database 12c is Oracle Multitenant. This feature allows you to create and maintain many pluggable
databases within an overarching multitenant container database. Following is a concise introduction to pluggable
terminology.
A multitenant container database (CDB) is defined as a database capable of housing one or more pluggable
databases. A container is defined as a collection of data files and metadata that exist within a CDB. A pluggable
database is a special type of container that can be easily provisioned by cloning another database. If need be,
a pluggable database can also be transferred from one CDB to another.
Every CDB contains a master set of data files and metadata known as the root container. Each CDB also contains
a seed container, which is used as a template for creating other pluggable databases. Each CDB consists of one master
root container, one seed container, and zero, or one or more, pluggable databases.
A pluggable enabled CDB must be created with the
ENABLE PLUGGABLE DATABASE
clause. A database that was not
created in this manner (a non-CDB) cannot contain pluggable databases. A non-CDB was the only type of database
available prior to Oracle Database 12c. Each CDB consists of the following elements:
CDB$ROOT
. The root contains the master set of data dictionary
views, which have metadata regarding the root as well as every child pluggable database
within the CDB.
•
One root container, named
PDB$SEED
. This container exists solely as a template for
providing data files and metadata used to create new pluggable databases within the CDB.
•
One static seed container, named
•
Zero, or one or more, pluggable databases (with a maximum of 252). Each pluggable database
is self-contained and functions like an isolated non-CDB database. Additionally, each
pluggable database contains its own data files and application objects (users, tables, indexes
and so on). When connected to a pluggable database, there is no visibility to the root container
or any other pluggable databases present within the CDB.
New with Oracle Database 12c there is a CDB level of data dictionary views that overarch the
DBA/ALL/USER
-level
views. The CDB-level views report across all containers (root, seed, and all pluggable databases) in a CDB. For
instance, if you wanted to view all users within a CDB database, you would do so from the root container, by querying
CDB_USERS
. If you're not using a CDB, then
DBA_USERS
is still an accurate view for reporting all user information. Many
of the data dictionary views now contain a new column, named
CON_ID
, that is a unique identifier for each container
within the CDB. The root container has a
CON_ID
of 1. The seed has a
CON_ID
of 2. Each new pluggable database
created within the CDB is assigned a unique sequential container ID.
Table
23-1
defines terms used in a pluggable database environment. Refer back to this table as you read through
this chapter.
