Ctrlk
For the complete documentation index, see llms.txt. This page is also available as Markdown.

Multitenant Architecture

About

Oracle introduced the Multitenant Architecture beginning with Oracle Database 12c as a major shift from the traditional single-instance model. Instead of running one database per instance, Oracle allows a single Container Database (CDB) to host multiple Pluggable Databases (PDBs).

This approach brings database consolidation, easier management, and better resource utilization. It is especially important in cloud environments and large enterprises where hundreds of applications may need separate databases but administrators want a centralized way to manage them.

In essence:

  • The CDB acts as the main container, holding Oracle’s system metadata and common components.

  • Each PDB is a self-contained database with its own schemas, users, and application data, but sharing the common Oracle binaries and background processes of the CDB.

The model is comparable to a building with multiple apartments:

  • The CDB is the building itself, providing the structure, utilities, and security.

  • Each PDB is like an apartment — independent, portable, and customizable for its resident (application or tenant).

By separating common system functions from individual databases, Oracle enables:

  • Easier upgrades and patching (apply once to CDB, all PDBs benefit).

  • Better isolation (issues in one PDB don’t affect others).

  • Rapid provisioning and portability (plug/unplug PDBs).

Key Components

Oracle’s multitenant model is built around a container-and-pluggable structure. The main elements are:

1. Container Database (CDB)

  • The central database that houses Oracle system metadata, background processes, and system tablespaces.

  • Contains one or more PDBs.

  • Includes special containers like CDB$ROOT and PDB$SEED.

2. Root Container (CDB$ROOT)

  • The root of the multitenant structure.

  • Stores common data dictionary and metadata needed by the entire CDB.

  • Holds system users, metadata, and shared Oracle components.

  • Common users (those prefixed with C##) are defined here.

3. Pluggable Database (PDB)

  • A portable, self-contained collection of schemas, objects, and users.

  • Each PDB appears to applications as a fully functional Oracle database.

  • Application users and schemas are typically created here.

4. Seed Database (PDB$SEED)

  • A special, read-only PDB provided by Oracle.

  • Acts as a template for creating new PDBs quickly.

  • Saves time by cloning instead of building databases from scratch.

5. Users in Multitenant

  • Common Users: Exist in all containers, created in the root (e.g., C##ADMIN).

  • Local Users: Exist only in a specific PDB, usually where applications are deployed (e.g., PRANAY).

Last updated