May 2, 2016

How To Relocate a PDB in Oracle Database 12c Release 2


This article will guide you through the steps to relocate a PDB by moving it between two root containers with near zero-downtime. The process is similar to performing a remote clone of a PDB.





Prerequisites
Note: In this context, the word "local" refers to the destination or target CDB that will house the relocated PDB. The word "remote" refers to the PDB that is to be relocated.


  • The user in the local database must have the CREATE PLUGGABLE DATABASE privilege in the root container.
  • The remote CDB must use local undo mode. Without this you must open the remote PDB.
  • The remote and local databases should be in archivelog mode.
  • The local database must have a public database link to the remote CDB using a common user.
  • The common user in the remote database that the database link connects to must have the CREATE PLUGGABLE DATABASE and SYSDBA or SYSOPER privilege.
  • The local and remote databases must have the same endianness.
  • The local and remote databases must either have the same options installed, or the remote database must have a subset of those present on the local database.
  • If the character set of the local CDB is AL32UTF8, the remote database can be any character set. If the local CDB does not use AL32UTF8, the character sets of the remote and local databases much match.
  • If the remote database uses Transparent Data Encryption (TDE) the local CDB must be configured appropriately before attempting the relocate. If not you will be left with a new PDB that will only open in restricted mode.
  • Bug 19174942 is marked as fixed in 12.2. I can't confirm this, so just in case I'll leave this here, but it should no longer be the case. The default tablespaces for each common user in the remote PDB *must* exist in local CDB. If this is not true, create the missing tablespaces in the root container of the local PDB. If you don't do this your new PDB will only be able to open in restricted mode (Bug 19174942).

I have two databases running on the same virtual machine as an example for this guide, but they could be running on separate physical or virtual servers.
  • cdb1 : The local database that will eventually house the relocated PDB.
  • cdb3 : The remote CDB that houses the PDB (pdb5) to be relocated.


Prepare Remote CDB

Connect to the remote CDB and prepare the remote PDB for relocating.
export ORAENV_ASK=NO
export ORACLE_SID=cdb3
. oraenv
export ORAENV_ASK=YES

sqlplus / as sysdba
Create a user in the remote database for use with the database link. In this case, we must use a comon user in the remote CDB.
CREATE USER c##remote_clone_user IDENTIFIED BY remote_clone_user CONTAINER=ALL;
GRANT CREATE SESSION, SYSOPER, CREATE PLUGGABLE DATABASE TO c##remote_clone_user CONTAINER=ALL;
Check the remote CDB is in local undo mode and archivelog mode.
COLUMN property_name FORMAT A30
COLUMN property_value FORMAT A30

SELECT property_name, property_value
FROM   database_properties
WHERE  property_name = 'LOCAL_UNDO_ENABLED';

PROPERTY_NAME                  PROPERTY_VALUE
------------------------------ ------------------------------
LOCAL_UNDO_ENABLED             TRUE

SQL>


SELECT log_mode
FROM   v$database;

LOG_MODE
------------
ARCHIVELOG

SQL>
Because the remote CDB is in local undo mode and archivelog mode, we don't need to turn the remote database into read-only mode.


Prepare Local CDB

Switch to the local server and create a "tnsnames.ora" entry pointing to the remote CDB for use in the USING clause of the database link. The connection details must include the "(SERVER = DEDICATED)" entry, or you will receive a "ORA-01031: insufficient privileges" error.
CDB3 =
(DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = my-server.my-domain)(PORT = 1521)) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = cdb3) ) )
Connect to the local database to initiate the relocate.
export ORAENV_ASK=NO
export ORACLE_SID=cdb1
. oraenv
export ORAENV_ASK=YES

sqlplus / as sysdba
Check the local CDB is in local undo mode and archivelog mode.
COLUMN property_name FORMAT A30
COLUMN property_value FORMAT A30

SELECT property_name, property_value
FROM   database_properties
WHERE  property_name = 'LOCAL_UNDO_ENABLED';

PROPERTY_NAME                  PROPERTY_VALUE
------------------------------ ------------------------------
LOCAL_UNDO_ENABLED             TRUE

SQL>


SELECT log_mode
FROM   v$database;

LOG_MODE
------------
ARCHIVELOG

SQL>
Create a public database link in the local CDB, pointing to the remote CDB.
Remember to remove this once the relocate is complete. It is a massive security problem to leave this in place!
DROP PUBLIC DATABASE LINK clone_link;

CREATE PUBLIC DATABASE LINK clone_link
  CONNECT TO c##remote_clone_user IDENTIFIED BY remote_clone_user USING 'cdb3';

-- Test link.
DESC user_tables@clone_link


Relocate a PDB

Create a new PDB in the local CDB by relocating the remote PDB. In this case we are using Oracle Managed Files (OMF), so we don't need to bother with FILE_NAME_CONVERTparameter for file name conversions.
CREATE PLUGGABLE DATABASE pdb5 FROM pdb5@clone_link RELOCATE;

Pluggable database created.

SQL>
We can see the new PDB has been created, but it is in the MOUNTED state.
COLUMN name FORMAT A30

SELECT name, open_mode FROM v$pdbs WHERE name = 'PDB5';

NAME                           OPEN_MODE
------------------------------ ----------
PDB5                           MOUNTED

SQL>
The PDB is opened in read-write mode to complete the process.
ALTER PLUGGABLE DATABASE pdb5 OPEN;

SELECT name, open_mode FROM v$pdbs WHERE name = 'PDB5';

NAME                           OPEN_MODE
------------------------------ ----------
PDB                            READ WRITE

SQL>
Drop the public database link.
DROP PUBLIC DATABASE LINK clone_link;
As with any PDB clone, check common users and the temporary tablespace is configured as expected.
If we switch back to the remote instance we can see PDB5 has been dropped.
export ORAENV_ASK=NO
export ORACLE_SID=cdb3
. oraenv
export ORAENV_ASK=YES

sqlplus / as sysdba


SELECT name, open_mode FROM v$pdbs WHERE name = 'PDB5';

no rows selected

SQL>


Managing Connections

Moving the database is only one aspect of keeping a system running. Once the database is in the new location, you need to make sure connections can still me made to it. The options are as follows.
  • If your connection information is centralised in an LDAP server (OID, AD etc.) then the definition can be altered centrally.
  • If both CBSs use the same listener, the relocated PDB will auto-register once the relocate is complete.
  • If both CDBs use different listeners, the LOCAL_LISTENER and REMOTE_LISTENER parameters can be used to configure cross-registration.

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