CDB is an acronym for “Container Database” and PDB is an acronym for “Pluggable Database”.I think it will be easier to explain with a metaphor for DBAs. Each container could be having different contents, with delivery target for different customers and completely packed/sealed independently with customer options but the entire freight is carried by a single engine or carrier at the front.I really think this new feature has lot of advantages from small customers to large scale enterprise customers no matter how we look at it.It is going to make the enterprises to become smarter in terms of utilizing the compute capacity what they have.Each PDB is a sealed container in a 250 freight container train or CDB as I explained before.Each RAC instance opens the CDB as a whole so that versions would be same for CDB as well as for all of the PDBs. Pluggable database is if fully compatible with all the database options and features including resource manager.Oracle has leap forwarded the middleware technologies especially the database technology into the cloud.
multiple customer or different entities data within the same database.
So you can have up to 250 pluggable databases or PDBs within one container database or CDB.
It is clear that there is one-to-many relationship between CDB and PDBS.
I will refer PDB and CDB to refer pluggable database and container database respectively.
Before we delve into deeper details about CDB and PDB, let us get some basic details about multi-tenancy.We can call it as a architecture which enables the PDB to keep its own dictionary and makes it easy to be portable between multiple CDBs.