‘STUB’ STATUS in DBA_PDBS

While exploring CDB  fleet in Oracle database 18c, I configured a CDB fleet having LCDB as the lead CDB and MCDB1 as a member CDB which hosts a PDB MPDB11.  As a result, proxy PDBs were automatically created for MCDB1 and MPDB11 in the lead CDB LCDB. When I queried STATUS column of DBA_PDBS  from root of LCDB, I encountered the value ‘STUB’ in  STATUS column in DBA_PDBS  as shown below:

SYS_LCDB>SELECT pdb_id, pdb_name, status, is_proxy_pdb "IS_PROXY_PDB" FROM dba_pdbs;
PDB_ID PDB_NAME STATUS IS_PROXY_PDB
---------- ---------- ------ ------------
3 LPDB1 NORMAL NO
2 PDB$SEED NORMAL NO
4 mcdb1 STUB YES
5 MPDB11 STUB YES 

As per oracle documentation (https://docs.oracle.com/en/database/oracle/oracle-database/18/refrn/DBA_PDBS.html#GUID-439126EA-A6B6-45B8-AAFA-37EE4356BBEF), the value ‘STUB’ is not listed. However, I came across an oracle tutorial showing how to configure a CDB fleet which mentions:

The STUB value in the STATUS column defines the CDB and its PDBs as members in the fleet.

On further exploring, I learnt that the proxy PDBs created for member CDBs/PDBs are not real proxies as   data files for SYSTEM, SYSAUX and UNDO tablespaces are not created locally in the lead CDB.  Consequently,  it is not possible to switch to or open the proxy PDBs in the lead CDB. Hence, they have a status of ‘STUB’ in status column of DBA_PDBS in the lead CDB.

Summary:

In a CDB fleet,

  • Proxy PDBs are automatically created for member CDBs and their PDBs in the lead CDB .
  • Proxy PDBs created for member CDBs/PDBs are not real proxies as   data files for SYSTEM, SYSAUX and UNDO tablespaces are not created locally in the lead CDB.
  • It is not possible to switch to or open the proxy PDBs in the lead CDB. Hence, they have a status of ‘STUB’ in status column of DBA_PDBS in the lead CDB.

Related Links:

CDB Fleet In Oracle Database 18c

References:

https://docs.oracle.com/en/database/oracle/oracle-database/18/qlaas/

Your comments and suggestions are welcome!