Oracle 19c Multitenant – Categorized FAQ

🔹 Basics (Core Concepts)

Multitenant architecture is based on two key components — Container Database (CDB) and Pluggable Database (PDB).

Multiple PDBs share the same SGA and background processes of the CDB. This design allows consolidation and resource efficiency.

• Represents the full Oracle database instance.
• Stores metadata for all PDBs.
• Contains control files, redo logs, undo, and system data dictionary.

• A self-contained database inside a CDB.
• Has its own SYSTEM, SYSAUX, and USERS tablespaces.
• Shares background processes, undo, and redo with the CDB.

The CDB$ROOT container stores metadata and system objects used by the entire CDB.

PDB$SEED is Oracle’s template PDB, used for creating new PDBs. It cannot be altered or dropped.

🔹 Administration Topics

• Reduced memory and process overhead.
• Easy patching and upgrades.
• Faster cloning and provisioning.
• Logical isolation between PDBs.

• Datafiles: Separate for root and each PDB.
• Control files, redo logs: Common for all.
• Undo: Shared from CDB.
• Temp tablespace: Common or separate.
• Character set: One for all PDBs.

SQL> SELECT NAME, CDB FROM V$DATABASE;

If CDB = 'YES', Multitenant option is enabled.

SQL> SELECT CON_ID, NAME, OPEN_MODE FROM V$PDBS;

ALTER SESSION SET CONTAINER=PDB$SEED;
SHOW CON_NAME;

🔹 Clone & Environment Topics

SHOW CON_NAME;
SELECT SYS_CONTEXT('USERENV','CON_NAME') FROM DUAL;

To connect to CDB:

sqlplus / as sysdba
ALTER SESSION SET CONTAINER=CDB$ROOT;

To connect to PDB:

sqlplus user/password@PDBNAME

Oracle recommends AL32UTF8 for new Multitenant installations.

• Datafiles: Separate per PDB
• Redo Logs, Control Files, Undo: Common
• Temp Tablespace: Common or Separate
• Password File: Shared

SQL> SHOW PDBS;
SQL> SELECT NAME, OPEN_MODE FROM V$PDBS;