Plugging In To Oracle 12c

Oracle 12C is over a year old now, so even firms wary of change are anxious to start taking advantage of its new features and capabilities. With the arrival of the first patch set release for in-memory enhancement, it’s time to utilize some of the most exciting concepts–Container Databases (CDB) and Pluggable Databases (PDB). Pluggable databases give administrators enormous flexibility in large and shared systems—to make best use of shared resources without sacrificing a database’s self-contained identity.

How does it work?

Let’s start from the bottom up, with the Pluggable database. PDBs are complete databases, with their own catalogs and tablespaces. Because they are self-contained, they can easily be moved or cloned onto different systems as needs change, or to propagate test systems quickly.

One or more PDBs are plugged into a Container database. The Container is a regular database, but its process structures are shared by the PDBs it holds—things like SGA and PGA, redo logs, etc. That means fewer processes to manage, fewer upgrades to think about, and better use of increasingly large pools of memory and processor strength.

Making it happen

There are lots of ways to plug, copy, and unplug, but creation from an existing database is easy too. In fact, it can be done in just a few commands. The following example shows how you create a pdb from seed:

SQL> alter system set PDB_FILE_NAME_CONVERT =’/u01/datafiles/pdbseed/’,’/u01/datafiles/Anuj/’ scope=both;

System altered.

SQL> CREATE PLUGGABLE DATABASE Anuj ADMIN USER PDB_Anj IDENTIFIED BY PDB_Anj default tablespace users datafile ‘/u01/datafiles/Anuj/users_01.dbf’ size      1000M;ROLES=(DBA);

Pluggable database created.

SQL> alter pluggable database Anuj open;

Now you’ve created a pluggable database. So what changes do you have to make to your code? None. Remember, a PDB is still a true database, not just a schema, despite the shared process and memory space. No application alterations are required now that it’s pluggable. Cloning to a new destination is just as simple with similar commands.

As always, there are implications to be aware of. Unsurprisingly, there are charges associated with additional databases in a single container. And, while PDBs sharing a container mean more applications per physical server, they also bind those applications together for startup, shutdown, and upgrade. For many, though, those tradeoffs are more than worth it for the ability clone to remote servers and maximize their efficiency.

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