Question

What is pluggable database (PDB) in Oracle 23ai

Answer 1

A Pluggable Database (PDB) is a self-contained, portable collection of schemas, objects, and related database structures that resides within a larger Container Database (CDB) in Oracle's Multitenant Architecture. This architecture, introduced in Oracle Database 12c, allows multiple PDBs to share a single CDB's system resources (memory, processes, etc.) while maintaining data isolation and independent management capabilities.

Key Concepts of PDB

1. Container Database (CDB):

   • A CDB is the top-level database that houses multiple PDBs. It contains the root container (CDB$ROOT) and optionally a seed PDB (PDB$SEED), which serves as a template for creating new PDBs.
   • The root container stores shared metadata and system information used by all PDBs.

2. Pluggable Database (PDB):

   • A PDB is a fully functional, self-contained database that resides within the CDB.
   • Each PDB has its own:
     • User schemas.
     • Tablespaces.
     • Metadata.
     • Security policies.

3. Isolation:

   • Each PDB operates independently from other PDBs in terms of security, schemas, and user management.
   • However, all PDBs share the same database instance, including memory and background processes.

4. Portability:

   • PDBs can be easily unplugged from one CDB and plugged into another, making it ideal for consolidating and migrating databases.

5. Seed PDB (PDB$SEED):

   • A read-only template PDB used for creating new PDBs.
   • It is automatically included in every CDB.

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Advantages of PDBs

1. Database Consolidation:

   • Multiple PDBs can run within a single CDB, reducing resource usage compared to running multiple standalone databases.

2. Ease of Migration:

   • PDBs can be unplugged from one CDB and plugged into another, facilitating easy database migration.

3. Independent Management:

   • Each PDB can be backed up, restored, and managed independently of other PDBs.

4. Resource Sharing:

   • PDBs share memory and processes of the CDB, which reduces overhead and improves resource utilization.

5. Cost Efficiency:

   • Ideal for consolidating databases in environments with Oracle Multitenant licensing, reducing operational costs.

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Common Use Cases

1. Database Consolidation:

   • Organizations consolidating multiple databases into a single infrastructure to reduce resource usage and licensing costs.

2. Development and Testing:

   • Developers can create multiple isolated environments for testing within a single CDB.

3. Simplified Upgrades:

   • Upgrading the CDB automatically applies to all PDBs.

4. Cloud and Multitenancy:

   • Cloud service providers use PDBs to deliver Database-as-a-Service (DBaaS) to multiple customers, maintaining isolation.

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Example: Viewing and Switching to a PDB

1. List All PDBs

To see all PDBs in a CDB:

SELECT name, open_mode FROM v$pdbs; 

2. Switch to a PDB

To switch to a specific PDB, e.g., FREEPDB1:

ALTER SESSION SET CONTAINER = FREEPDB1; 

3. Work Inside the PDB

Once connected, all operations will be scoped to the selected PDB.

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Summary

A Pluggable Database (PDB) provides a way to manage and consolidate multiple databases within a single Oracle Database instance (CDB). It simplifies database management, reduces costs, and enhances flexibility for operations like migration and resource sharing.