Oracle Architecture - Oracle Essentials - page 44

multitenant container database or pluggable database, as well as additional information
related to pluggables, which are described in the next section.
Pluggable Databases
All of the structures listed above have been a part of the Oracle Database since the first
publication of this topic, more than 10 years ago. Oracle Database 12 c introduces a new
structural concept, the pluggable database , included as part of a feature called the Mul‐
titenant database, which provides another layer of separation within a single database
instance.
The concept behind pluggable databases is straightforward—a pluggable database is a
layer of isolation between a database instance and a schema. Those operations and
entities that apply to an instance are implemented at the level of the multitenant con‐
tainer database (CDB) and operate across multiple separate pluggable databases (PDBs).
This separation increases the flexibility of privilege and responsibility assigned to a
pluggable database, while not having to also increase the operational overhead associ‐
ated with an instance. The separation also makes it quicker and easier to create a new
pluggable database and to upgrade pluggable databases by simply plugging them into
an upgraded CDB.
Schemas live within a PDB. Since a PDB can support multiple schemas, pluggable da‐
tabases are a good tool to use for database consolidation, since they can support the
complete structures of applications with multiple schemas without concern for conflicts
within a single database instance. In effect, a PDB is a logically distinct database within
an Oracle instance. The CDB can contain users and roles that are common across PDBs.
Even better, in terms of consolidation, multiple PDBs share common database back‐
ground processes, which means that multiple PDBs in a single instance require fewer
resources than the multiple isolated instances.
All data and metadata for a PDB are stored within the PDB. This organization means
that you will be able to unplug a PDB from one Oracle Database instance and plug it
into another instance transparently, simplifying support of multiple environments such
as for develop and test purposes. You will even be able to upgrade a PDB by simply
moving it from one CDB to another CDB that has been upgraded.
Implementation
Oracle Database 12 c will allow for a single-tenant version, which includes a single PDB
in a CDB, or multiple PDBs with the Oracle Multitenant Option.
All CDBs come with a seed PDB, which is used as the template for other PDBs that are
created by an instance administrator. You can move PDBs from one CDB to another,
or plug in a non-PDB database to an Oracle Database 12 c instance that supports PDBs,
which will transform it into a PDB. You can also clone an existing PDB to create a copy.