About oracle mulittenant environment

The multitenant architecture enables an Oracle database to function as a multitenant container database (CDB) that includes zero, one, or many customer-created pluggable databases (PDBs). A PDB is a portable collection of schemas, schema objects, and nonschema objects that appears to an Oracle Net client as a non-CDB. All Oracle databases before Oracle Database 12c were non-CDBs.

This section contains the following topics:

• Components of a CDB
• Common Users and Local Users
• Separation of Duties in CDB and PDB Administration

Components of a CDB

A CDB includes the following components:

• Root

  The root, named CDB$ROOT, stores Oracle-supplied metadata and common users. An example of metadata is the source code for Oracle-supplied PL/SQL packages. A common user is a database user known in every container. A CDB has exactly one root.

• Seed

  The seed, named PDB$SEED, is a template that you can use to create new PDBs. You cannot add objects to or modify objects in the seed. A CDB has exactly one seed.

• PDBs

  A PDB appears to users and applications as if it were a non-CDB. For example, a PDB can contain the data and code required to support a specific application. A PDB is fully backward compatible with Oracle Database releases before Oracle Database 12c.

Each of these components is called a container. Therefore, the root is a container, the seed is a container, and each PDB is a container. Each container has a unique container ID and name within a CDB. Figure 1 shows a CDB with several PDBs.

Figure 1 CDB with PDBs

You can easily plug a PDB into a CDB and unplug a PDB from a CDB. When you plug in a PDB, you associate the PDB with a CDB. When you unplug a PDB, you disassociate the PDB from a CDB. An unplugged PDB consists of an XML file that describes the PDB and the PDB‘s files (such as the data files and wallet file).

You can unplug a PDB from one CDB and plug it into a different CDB without altering your schemas or applications. A PDB can be plugged into only one CDB at a time.

Each PDB has a globally unique identifier (GUID). The PDB GUID is primarily used to generate names for directories that store the PDB‘s files, including both Oracle Managed Files directories and non-Oracle Managed Files directories.

Common Users and Local Users

A CDB supports common users. A common user is a user that has the same identity in the root and in every existing and future PDB. A common user can log in to the root and any PDB in which it has privileges. The operations that a common user can perform depend on the privileges granted to the common user. Some administrative tasks, such as creating a PDB or unplugging a PDB, must be performed by a common user. A CDB also supports local users. A local user is a user that exists in exactly one PDB.

Separation of Duties in CDB and PDB Administration

Some database administrators manage the entire CDB. These database administrators connect to the CDB as common users, and they manage attributes of the entire CDB and the root, as well as some attributes of PDBs. For example, these database administrators can create, unplug, plug in, and drop PDBs. They can also specify the temporary tablespace for the entire CDB and the default tablespace for the root, and they can change the open mode of one or more PDBs.

Database administrators can also connect to a specific PDB as a local user and then perform a subset of management tasks on the PDB that a database administrator performs on a non-CDB. The subset of tasks are those required for the PDB to support an application. For example, these can include management of tablespaces and schemas in a PDB, specification of storage parameters for that PDB, and changing the open mode of the current PDB.

Purpose of a Multitenant Environment

A multitenant environment enables the central management of multiple PDBs in a single installation. By using a multitenant environment, you can accomplish the following goals:

• Cost reduction

  By consolidating hardware and sharing database memory and files, you reduce costs for hardware, storage, availability, and labor. For example, 100 PDBs on a single server share one database instance and one set of database files, thereby requiring less hardware and fewer personnel.

• Easier and more rapid movement of data and code

  By design, you can plug a PDB into a CDB, unplug the PDB from the CDB, and then plug this PDB into a different CDB. Therefore, you can easily move an application‘s database back end from one server to another.

• Easier management and monitoring of the physical database

  The CDB administrator can attend to one physical database (one set of files and one set of database instances) rather than split attention among dozens or hundreds of non-CDBs. Backup strategies and disaster recovery are simplified.

• Separation of data and code

  Although consolidated into a single physical CDB, PDBs mimic the behavior of traditional non-CDBs. For example, if a user error causes data loss, then a PDB administrator can use point-in-time recovery to retrieve the lost data without affecting other PDBs.

• Ease of performance tuning

  It is easier to collect performance metrics for a CDB than for multiple non-CDBs. It is easier to size one SGA than several SGAs.

• Support for Oracle Database Resource Manager

  In a CDB, one concern is contention for system resources among the PDBs running on the same server. Another concern is limiting resource usage for more consistent, predictable performance. To address such resource contention, usage, and monitoring issues, you can use Oracle Database Resource Manager (see Chapter 44, "Using Oracle Resource Manager for PDBs with SQL*Plus").

• Fewer patches and upgrades

  It is easier to apply a patch to one CDB than to multiple non-CDBs and to upgrade one CDB than to upgrade several non-CDBs.

A multitenant environment is especially useful when you have many non-CDBs deployed on different hardware in multiple Oracle Database installations. These non-CDBs might use only a fraction of the hardware resources dedicated to them, and each one might not require a full-time database administrator to manage it.

By combining these non-CDBs into a CDB, you can make better use of your hardware resources and database administrator resources. In addition, you can move a PDB from one CDB to another without requiring changes to the applications that depend on the PDB.

Tasks for a Multitenant Environment

Task 1 Planning for CDB Creation

Below tables contains contant you need to consider while planning for a CDB.

Task 2   Create One or More CDBs

Oracle Multitenant Environment