Oracle Multitenant and the pluggable database architecture was the big new feature in 12c when was released in 2013. This architecture change brought the notions of Container Databases (CDB) and Pluggable databases (PDB), with the possibility to perform actions such as backups and patching at the CDB level, and allow a PDB to be easily moved from one server to another (to another CDB).
Having more than one PDB in a CDM becomes a multi-tenant architecture allowing for consolidation and easier management. All that sounds great, but multi-tenant is not a base feature, it is a paid option on top of the Enterprise Edition Database, costing roughly 40% of the database licence.
For that reason this major new feature went ignored by many clients and they continued using the non-CDB architecture. Looking carefully at the 12c documentation, non-CDB architecture was deprecated. It still works and is still fully supported, but it's Oracle way of saying we should move on.
Oracle OpenWorld presentations from this week show that in the next version, 20c (just round the corner), non-CDB architecture will be de-supported, forcing everyone into the CDB/PDB architecture. So, it's time to get up to speed and understand what it means for your environment.
The good news is that 19c now allows 3 PDBs without requiring a mulit-tenant licence. For 4 or more PDBs, a multi-tenant license is required. This is great news, clients that found multi-tenant to be prohibitively expensive can now start consolidating - even on Standard Edition (which never had the multi-tenant option before).
However.. do you think Oracle blocks you from adding a 4th PDB? Of course not! So while it is good news, it can also be a licensing compliance risk - it becomes easier to unplug and plug databases into containers, and easy to create 4 PDBs without having a mulit-tenant licence.
You need to add this to your Oracle licensing check list.. you do have one of those right?!