Database Reference
In-Depth Information
Figure 7-3.
An overview of the Container Database
To begin with, the main differentiator is the fact that you can see at least one Pluggable Database in addition to
the root already. The database you see to the left is a special one, called the seed database. If you decided to create
PDBs during the CDB creation then there can be additional PDBs, up to 253 in total for Oracle 12.1.
When thinking about the PDB-CDB relationship one could use the analogy to Solaris zones. Every modern
Solaris installation will consist of a global zone. The global zone is what resembles the root-container in the Container
Database. The recommendation is not to use the global zone to store applications, and that's exactly the same with the
CDB. Storing data in the root zone is as bad as creating applications in the global zone, as it defeats the main purpose
of the self-contained unit. You would not store user data in the SYSTEM tablespace either, would you?
Only one listener is required on the database host for single instance Oracle deployments, which will manage
connections between applications, ad-hoc query users and generally speaking all other database server to client
traffic. When a PDB is opened, a service is started by default which is named after the PDB. Additional services can
easily be created to allow for fine-grained charge back models.
Containers
After initial creation of the Container Database, i.e., the top-level container for all components to be stored, you find
yourself in a new territory ready to be explored. Since the concept of Pluggable Databases has not existed in Oracle,
even from a conceptual point of view it takes a little time to familiarize yourself with the new world.
At first, you need to understand the concept of a container. The container is your namespace, i.e., the scope of
the statements you issue. The introduction of the container is not a problem for application owners and developers
as you will see shortly, but more of an issue to the database administrator. You need to know which container you are
currently connected to. The simple rule to remember: if you used the command “sqlplus / as sysdba” you are in the
root container, or CDB$ROOT.
Search WWH ::
Custom Search