Rights and Roles

Management of users and roles is, of course, critical in a highly consolidated environment. When using pluggable databases, you need to distinguish between common and local users and roles. Users and roles are considered common – or rather global  – if they are created at CDB level and therefore inherited by all existing and future PDBs. You can identify these users by their prefix of C##. These global users can connect to each PDB to which they have access, thanks to respective grants. At the PDB level, rights can be extended beyond those authorizations derived from common roles. Thus, it is possible to give a global user DBA privileges in one database while that same user cannot even connect with any other database.

The link between users and databases is handled by the Listener process or via the Scan Listener, just as in older releases. By default, precisely one service with the same name exists for each pluggable database, but more services can be added.

Limitations

With all of these advantages, limitations are bound to occur in the operation of this environment. Obviously, all PDBs that share a CDB must use the same database version, and all databases must use the same character set – different character sets are not possible. The obvious choice here is Unicode: To facilitate migration to Unicode, the maximum column width of a VARCHAR2 column has been expanded from 4Kb to 32Kb as a new feature in 12c. Errors that were previously caused by reaching the maximum column width when converting to Unicode are thus a thing of the past.

At the same time, there are restrictions on the individually modifiable database parameters per pluggable database. An overview of the modifiable parameters can be obtained with the query:

select name from v$parameter where ISPDB_MODIFIABLE ='TRUE' order by 1

Mainly the tuning parameters, such as OPTIMIZER_*** and PARALLEL_***, and the NLS parameters are customizable for each PDB.

Support for Cloud Architecture

Considering the fact that this version is the first to make multitenant architecture available with container and pluggable databases, support by the Oracle tools is already advanced. For example, the pluggable database is completely Real Application Cluster (RAC)-capable; RMAN can handle backups and restores at PDB level  – including recovery down to table level. Additionally, integration into standby databases with Data Guard [6] is supported. The only restriction for Data Guard is that a move is only possible at container level, and automatic integration of a new PDB on the standby site is only possible in conjunction with the commercial Active Data Guard option.