Oracle multitenant database architecture gives the ability to virtualize oracle database implementations, similarly to OS virtualization.   The multitenant architecture has two main components:  The CDB – Container Database and PDB – Pluggable database.  These two components have many aspects which help to describe their architecture and are detailed below:

CDB – Container Database

1. CDB is commonly referred to as the root container.
2. One root container in any implementation and contains all oracle provided metadata and common user.
3. CDB$ROOT is the name of the root container.
4. All PDBs belong to a single root container.
5. User or application data should never stored in the root.
6. You can have common users for system administration in root that crosses all PDB in the root container.
7. One seed PDB exist in all root containers, Oracle supplies this template to create new PDB.

PDB – Pluggable Database

1. PDB$SEED is the name of the seed PDB in all root container databases.
2. You cannot add or modify objects in PDB$SEED.
3. Zero or more user-created PDBs in CDB.
4. PDBs are entities that contain application data and code for specific features.
5. PDBs do not contain oracle supplied metadata or common users.
6. No PDBs exist at CDB creation.
7. PDBs are uniquely named in a CDB.
8. PDBs name must be unique across multiple CDB if using the same listener.

Larry Catt

OCP

As of Oracle 12c release 12.1.0.2  the following features are not supported for use in CDB instances.

1. Database Change Notification
2. Continuous Query Notification (CQN)
3. Client Side Cache
4. Heat Map
5. Automatic Data Optimization
6. Oracle Streams
7. Oracle Fail Safe
8. Flashback Pluggable Database (Flashback Database works but will flashback CDB$ROOT including all PDBs)
9. DBVERIFY
10. Data Recovery Advisor (DRA)
11. Flashback Transaction Backout

Larry Catt

OCP

12c release has given us the ability to virtualize databases.   These procedure outlines three methods to move a stand-alone database to a 12c PDB.   Each of these methods have both positive and negatives aspects.  Careful thought, analysis and some testing should be performed before deciding which method is best for your situation.

Method 1 – DBMS_PDB package.

DBMS_PDB package is provided with Oracle 12c RDBMS release.  It provides multiple procedures for checking, preparing, creating conversions, and cleaning up after movement of standalone database to PDB.

Pros:

1. Removes guess work from conversion process.
2. No coding on administrators part.
3. No need to create PDB before procedure.

Cons:

1. No ability to transform data elements.

Method 2 – Data Pump

Use the EXP/IMP to extract metadata and data from standalone database into PDB.

Pros:

1. EXP/IMP utility of data pump are well known.
2. Able to do inclusive/exclusive data movement.
3. Able to start and stop.

Cons:

1. Have to build CDB and PDB for destination.
2. Can requires disk space for exports.
3. Can be very time consuming.

Method 3 – Goldengate / ETL technology

Use Goldengate or other ETL tool to move data from existing standalone into PDB.

Pros:

1. Can be done online with minimal down time.
2. Is extremely flexible.
3. Able to start and stop.
4. Able to transform data during process.

Cons:

1. Have to build CDB and PDB for destination.
2. Expensive licensing cost.
3. Can be time consuming.

Larry Catt

OCP

New to Oracle 12c is the feature of multitenant databases or CBD/PDB implementation to add a form of Virtualization to the Oracle RDBMS world.    This new feature is designed to reduce the number of physical server machines currently required to house normal database suites.    It is fairly common to have a large number of small data stores in an organization to server various system needs and though the resource requirements of these data stores is relatively low, they still exist on a single VM or physical server.   CDB and PDB technology looks to resolve this issue by combining these databases into a single instance which appears to be stand-alone to the outside world.   This article lists and describes the benefits of a CDB/PDB implementation.

1. Database Consolidation – Multitenant Databases implementations can consolidate several small databases on separate servers into a CDB using one server. Allowing the organization to minimize the number of physical or virtual servers being used without reducing the number of application data stores being accessed.

2. Reduced Cost – Reduction in the number of physical and virtual machines in use saves money in hardware, labor costs, floor space, and a multitude of other ways.

3. Rapid Implementation – Implementation of a new data store or the movement of existing database is significantly reduced both in complexity and resource requirements. New PDB can be created on the fly to test various applications and removed when no longer needed.

4. Simplified Management – Reduced number of servers and database instances easies the burden placed on administrators and management to ensure proper operations of a data center. Thus allowing of an increased level of performance to end users.

5. Separation of administrative duties – Administration of the CDB and PDB are branched along resource lines where CDB control memory and processes and allocate them to various PDBs based on needs. CDB administration consists of managing performance related to OS and internal processes.  PDB administration is focused on performance related to application using the data store.   Thus creating a well-defined separation of administrative duties between CDB and PDB.   DBA responsible for CDB administration are focused on system/processes performance improvements and DBA responsible for individual PDB are focused on application implementation performance.

6. Simplified Patching – Patching/upgrade single CDB database which contains multiple PDBs and not multiple separate databases.

Larry Catt

OCP

The IT industry has increasing developed server technology with increased levels of memory and processing power which have out grown traditional system setups of one application to one server.  Most modern physical servers are very capable of handling multiple applications and even multiple server platforms through Virtualization technologies.   This is just as true with RDBMS suites.   Oracle has developed Multitenant architecture databases to take advantage of excess server power and reduce the physical hardware foot print.   This technology is known as CDB – Container Databases and PDB – Pluggable Databases.

Container Databases (CDB) act as the container where you store all of your application and system databases.  It contains and manages all of the initialization parameters, memory resources, processor resource and shared services granted to the RDBMS by the OS and created through the RDBMS.   Container Databases should not be used by application data stores to process user requests or perform any action for an outside application.   It should only be used to house PDB data stores which do provide data storage and manipulations of applications.  CDB’s can hold one to many PDBs.

Pluggable Databases (PDB) act as the application data stores and perform all actions that a traditional Oracle database perform through the use of resources granted by the CDB.   It allows us to reduce the overhead of managing multiple Oracle RDBMS Suites and increase the utilization of current hardware resources.  PDB’s are housed in a single CDB and can be moved from one CDB to another CDB.

Larry Catt

OCP