Overview

Multitenancy is a new concept in Oracle 12c. The basis of it is that, you can separate the application data from the system data. Up to and including 11g, all the data in the database was residing in the same dimension as the system data or any other data for that matter. Data related to different application, were in the same tablespaces or even managed by the same user. Well, from 12c, all this can go under the table, now you can have many databases PDBs (pluggable databases), inside one big database, the root container. There are even more possibilities like application containers and so on, but we will see that later.

With the multi-tenancy, we have a:

root container - Where the system data resides. Also you can choose if you want the UNDO tablespace in the root to be used for all PDBs, or each PDB to have its own undo, SYSTEM and SYSAUX tablespace, making it completely independent from the root container.

Application Container - Container which consist of 1 or many PDBs which host a specific application. We are able to assign versions and name to such container, furthermore we can initiate installation and upgrade modes.

Creation

Firstly, we need to create our container. From 12c, we can create a database to be either as it always has been, a normal database, OR we can create it to allow other databases as well. So it will be a container, let's see how we can do both:

Create Normal DB

Actually, the creation of a normal database isn't that hard, you can just type:

Create simple database

Simply that, will create us a normal database, well after that you will have to run the catproc and the catalog scripts, but you get the gist.

Create container DB

To create a container, database we NEED to allow it to have PLUGGABLE databases, as follows:

Create CDB

That will create us a container database called CDB1 and a SEED, after that you will have to run script:

@$ORACLE_HOME/rdbms/admin/catcdb.sql

But other than that, all will be ok. So we have a container, big deal, what then. Well, now we can create PLUGGABLE databases as follows:

Create Pluggable DB (PDB)

As I said before, pluggable databases, are totally separate databases from one another. Imagine it having many databases (PDBs) within one big database (CDB). These PDBs, can have separate user totally individual from each other. So let's see how it is done:

Create PDB

You can use either:

FILE_NAME_CONVERT, or

CREATE_FILE_DEST, or

PDB_FILE_NAME_CONVERT

Either in the session level or on the CREATE statement, up to you, the result will be the same.

Once created, you can list all PDBs in a certain CDB as follows:

List PDBs

Remember, 1 PDB can be in only 1 ROOT$CDB, but 1 CDB can have many PDBs. Furthermore, from 12.2, we have also applicational containers, which are containers within the CDB, but we will speak about them in a second.

Management

We can perform several actions with a PDB:

OPEN

Plug & Unplig

Close

Restore / Recover

Open

After we create a CDB, we need to open it, as follows:

Open PDB

That command, will open us a database and it will become available to the users. We can also close a pluggable database as follows:

Close PDB

Unplug a PDB

In 12.1 we could unplug a PDB into .xml file and the migration of the PDB, would be the migration of that XML file AND the relevant database files. From 12.2 we can also unplug the PDB into a .pdb archive file, which contains information about the PDB AND the relevant database files. That will ease our migration.

Unplug to .pdb file

That assumes, you are using OMF file. The resulting file contains all the necessary data:

List .pdb file

Plug a PDB

To plug a database, we need the file from above and we need to verify the compatibility as follows:

Plug a PDB

Create a PDB using the source file

Then we can create a PDB using the .pdb file as follows:

Plug-in PDB

Clone a PDB

We can clone a PDB as follows:

Cloning a PDB