36 Overview of Managing a Multitenant Environment

Become familiar with basic concepts related to a multitenant environment.

About a Multitenant Environment

You can use the Oracle Multitenant option to configure and manage a multitenant 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.

Components of a CDB

A CDB includes the root, the seed, and PDBs.

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 36-1 shows a CDB with several 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 container in which it has been granted CREATE SESSION privilege. 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.

See Also:

Oracle Database Security Guide for more information about common users and local users

Separation of Duties in CDB and PDB Administration

Some database administrators manage an entire CDB, while others manage individual PDBs.

The database administrators who manage an entire CDB 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 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 PDB administrator 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, changing the open mode of the current PDB, and setting PDB-level initialization parameters.

Purpose of a Multitenant Environment

A multitenant environment enables the central management of multiple PDBs in a single installation and enables you to accomplish several goals.

By using a multitenant environment, you can accomplish the following goals:

  • Cost reduction

    By consolidating hardware and database infrastructure to a single set of background processes, and efficiently sharing computational and memory resources, you reduce costs for hardware and maintenance.

  • 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 manage the environment as an aggregate by executing a single operation, such as patching or performing an RMAN backup, for all hosted tenants and the CDB root.

  • Separation of data and code

    Although consolidated into a single physical CDB, PDBs mimic the behavior of traditional non-CDBs. For example, a PDB administrator can flush the shared pool or buffer cache in the context of a PDB without affecting other PDBs in the CDB.

  • 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 any shared resource environment, administrators must manage system resources to provide a predictable environment for users and address unexpected or transient resource contention. To address these issues and to provide resource usage monitoring, you can use Oracle Database Resource Manager (see 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.

Prerequisites for a Multitenant Environment

Prerequisites must be met for a multitenant environment.

The following prerequisites must be met before you can create and use a multitenant environment:

  • Install Oracle Database 12c.

    The installation includes setting various environment variables unique to your operating system and establishing the directory structure for software and database files.

    See Oracle Database Installation Guide specific to your operating system.

  • Set the database compatibility level to at least 12.0.0.

    See Oracle Database Upgrade Guide for information about the database compatibility level.

Tasks and Tools for a Multitenant Environment

There are common tasks you perform for a multitenant environment, and you use tools to complete the tasks.

Tasks for a Multitenant Environment

A multitenant environment enables you to achieve several goals. Complete general tasks to configure and use a multitenant environment.

These goals are described in "Purpose of a Multitenant Environment". To do so, you must complete the following general tasks:

Task 1   Plan for the Multitenant Environment

Creating and configuring any database requires careful planning. A CDB requires special considerations. For example, consider the following factors when you plan for a CDB:

  • The number of PDBs that will be plugged into each CDB

  • The resources required to support the planned CDB

  • Container management policies executed as an aggregate on the entire CDB or executed locally on individual PDBs

See "Planning for CDB Creation" for detailed information about planning for a CDB.

Task 2   Create One or More CDBs

When you have completed the necessary planning, you can create one or more CDBs using either the Database Configuration Assistant (DBCA) or the CREATE DATABASE SQL statement. In either case, you must specify the configuration details for each CDB.

See "Using DBCA to Create a CDB" and "Using the CREATE DATABASE Statement to Create a CDB" for detailed information about creating a CDB.

After a CDB is created, it consists of the root and the seed, as shown in Figure 36-2. The root contains only Oracle maintained objects and data structures, and the seed is a generic seed database for cloning purposes.

Figure 36-2 A Newly Created CDB

Description of Figure 36-2 follows
Description of "Figure 36-2 A Newly Created CDB"
Task 3   Create, Plug In, and Unplug PDBs

PDBs contain user data. After creating a CDB, you can create PDBs, plug unplugged PDBs into it, and unplug PDBs from it whenever necessary. You can unplug a PDB from a CDB and plug this PDB into a different CDB. You might move a PDB from one CDB to another if, for example, you want to move the workload for the PDB from one server to another.

See Creating and Removing PDBs with SQL*Plus and Creating and Removing PDBs with Cloud Control for information about creating PDBs, plugging in PDBs, and unplugging PDBs.

Figure 36-3 shows a CDB with several PDBs.

Task 4   Administer and Monitor the CDB

Administering and monitoring a CDB involves managing the entire CDB, the root, and some attributes of PDBs. Some management tasks are the same for CDBs and non-CDBs, and some are different. See "After Creating a CDB" for descriptions of tasks that are similar and tasks that are different. Also, see Administering a CDB with SQL*Plus, Administering CDBs and PDBs with Cloud Control, and Viewing Information About CDBs and PDBs with SQL*Plus.

You can use Oracle Resource Manager to allocate and manage resources among PDBs hosted in a CDB, and you can use it to allocate and manage resource use among user processes within a PDB. See Using Oracle Resource Manager for PDBs with SQL*Plus.

You can also use Oracle Scheduler to schedule jobs in a CDB and in individual PDBs. See Using Oracle Scheduler with a CDB.

Task 5   Administer and Monitor PDBs

Administering and monitoring a PDB is similar to administering and monitoring a non-CDB, but there are some differences. See Administering CDBs and PDBs with Cloud Control, Administering PDBs with SQL*Plus, and Viewing Information About CDBs and PDBs with SQL*Plus.

Tools for a Multitenant Environment

You can use various tools to configure and administer a multitenant environment.

Use the following tools to complete tasks for a multitenant environment:

  • SQL*Plus

    SQL*Plus is a command-line tool that enables you to create, manage, and monitor CDBs and PDBs. You use SQL statements and Oracle-supplied PL/SQL packages to complete these tasks in SQL*Plus.

    See SQL*Plus User's Guide and Reference.

  • DBCA

    Oracle Database Configuration Assistant (DBCA) is a utility with a graphical user interface that enables you to configure a CDB, create PDBs, plug in PDBs, and unplug PDBs.

    See Oracle Database 2 Day DBA, Oracle Database Installation Guide, and the DBCA online help for more information about DBCA.

  • Oracle Enterprise Manager Cloud Control

    Cloud Control is a system management tool with a graphical user interface that enables you to manage and monitor a CDB and its PDBs.

    See the Cloud Control online help for more information about Cloud Control.

  • Oracle SQL Developer

    Oracle SQL Developer is a graphical version of SQL*Plus that gives database developers a convenient way to perform basic tasks.

    See Oracle SQL Developer User's Guide.

  • The Server Control (SRVCTL) utility

    The SRVCTL utility can create and manage services for PDBs.

    See "Managing Services Associated with PDBs".

  • EM Express


    PDB management with EM Express is available starting with Oracle Database 12c Release 1 (

    EM Express supports managing PDBs, including creating PDBs from the seed, cloning PDBs, plugging in PDBs, unplugging PDBs, and dropping PDBs. EM Express also supports basic resource management like setting CPU utilization and storage limits at the PDB level and changing the resource plan at CDB level.

    See Oracle Database 2 Day DBA for more information.

  • Oracle Multitenant Self-Service Provisioning application


    This feature is available starting with Oracle Database 12c Release 1 (

    This application enables the self-service provisioning of PDBs. CDB administrators control access to this self-service application and manage quotas on PDBs.

    For more information about the application or to download the software, use any browser to access the OTN page for the application:


    To access the application, click the Downloads tab, and select Multitenant Self-Service Provisioning in the Oracle Database 12c Multitenant Applications section.