Oracle 12c Multitenant Architecture

By: Juan Carlos Olamendy Turruellas

In this article, I want to talk about the architecture of the last version of Oracle database (version 12c) and in particular on the biggest architectural change: multitenant support. For the examples below, I will use the following box: Oracle database 12c running insideCentOS 6.4.

This new approach of Oracle (multitenant architecture) is also present on the version name 12c where the c letter stands for cloud. Let′s remind that the pillar of cloud computing is virtualization, where several virtual machines runs concurrently all hosted in physical machines deployed on the Web (the cloud). Each virtual machine has its own resources and it′s also independent of the host physical machine. And the good news is that the new concepts around the multitenant architecture of Oracle 12c are similar to virtualization, and they are: container database (CDB) and pluggable database (PDB) or a tenant. Doing some analogy, the CDB is like the physical host machine while the PDB is like virtual machines. Each PDB is independent each other; however all PDBs share the SGA memory and the background and foreground (user processes) processes as well as the data dictionary information (metadata), common roles, common users and common privileges. A PDB is used basically to encapsulate a sub-set of tables and indexes as well as local roles, local users and local privileges. Unlike the old Oracle databases (pre-12.1c version) where only one database can be mounted by an instance, the multitenant architect enable mount multiple databases (CDB) by an instance.

When Oracle database software is installed and it′s execute the SQL statement CREATE DATABASE, then the CDB is created. You can find out if the database is a CDB or PDB using the following statement:

Now let me show the logical view of the Oracle 12g multitenant architecture.