Announcement

Hot Clone a Remote PDB or Non-CDB in Oracle Database 12c Release 2


This article will guide you through the steps to hot cloning a remote pdb or non-cdb in oracle database 12c release 2 (12.2).






The initial release of Oracle Database 12c Release 1 (12.1.0.1) remote cloning of PDBs was listed as a feature, but it didn't work. The 12.1.0.2 patch fixed that, but also added the ability to create a PDB as a clone of a remote non-CDB database. The biggest problem with remote cloning was the prerequisite of placing the source PDB or non-CDB into read-only mode before initiating the cloning process. This made this feature useless for cloning production systems, as that level of down-time is typically unacceptable. Oracle Database 12c Release 2 (12.2) removes this prerequisite, which enables hot cloning of PDBs and non-CDBs for the first time.


Prerequisites
The prerequisites for cloning a remote PDB or non-CDB are very similar, so i will be handling them together.

Note: In this context, the word "local" refers to the destination or target CDB that will house the cloned PDB. The word "remote" refers to the PDB or non-CDB that is the source of the clone.

  • 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 or non-CDB in read-only mode.
  • The remote database should be in archivelog mode. Without this you must open the remote PDB or non-CDB in read-only mode.
  • The local database must have a database link to the remote database. If the remote database is a PDB, the database link can point to the remote CDB using a common user, the PDB or an application container using a local or common user.
  • The user in the remote database that the database link connects to must have the CREATE PLUGGABLE DATABASE 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 clone. 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).
  • When cloning from a non-CDB, both the the local and remote databases must using version 12.1.0.2 or higher.

I have three databases running on the same virtual machine as an example for this article, but they could be running on separate physical or virtual servers.
  • cdb1 : The local database that will eventually house the clones.
  • db12c : The remote non-CDB.
  • cdb3 : The remote CDB, used for cloning a remote PDB (pdb5).


Cloning a Remote PDB

Connect to the remote CDB and prepare the remote PDB for cloning.
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 will use a local user in the remote PDB.
CREATE USER c##remote_clone_user IDENTIFIED BY remote_clone_user CONTAINER=ALL;
GRANT CREATE SESSION, CREATE PLUGGABLE DATABASE TO c##remote_clone_user CONTAINER=ALL;
Check the remote CDB is in local undo mode and archivelog mode.
CONN / AS SYSDBA

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.
Switch to the local server and create a "tnsnames.ora" entry pointing to the remote database for use in the USING clause of the database link.
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 clone.
export ORAENV_ASK=NO
export ORACLE_SID=cdb1
. oraenv
export ORAENV_ASK=YES

sqlplus / as sysdba
Create a database link in the local database, pointing to the remote database.
DROP 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
Create a new PDB in the local database by cloning 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 pdb5new FROM pdb5@clone_link;

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 = 'PDB5NEW';

NAME                           OPEN_MODE
------------------------------ ----------
PDB5NEW                        MOUNTED

SQL>
The PDB is opened in read-write mode to complete the process.
ALTER PLUGGABLE DATABASE pdb5new OPEN;

SELECT name, open_mode FROM v$pdbs WHERE name = 'PDB5NEW';

NAME                           OPEN_MODE
------------------------------ ----------
PDB5NEW                        READ WRITE

SQL>
As with any PDB clone, check common users and the temporary tablespace is configured as expected.


Cloning a Remote Non-CDB

Connect to the remote database to prepare it for cloning.
export ORAENV_ASK=NO
export ORACLE_SID=db12c
. oraenv
export ORAENV_ASK=YES

sqlplus / as sysdba
Create a user in the remote database for use with the database link.
CREATE USER remote_clone_user IDENTIFIED BY remote_clone_user;
GRANT CREATE SESSION, CREATE PLUGGABLE DATABASE TO remote_clone_user;
Check the remote non-CDB is archivelog mode.
SELECT log_mode
FROM   v$database;

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

SQL>
In Oracle 12.1 we would have switched the remote database to read-only mode before continuing, but this is not necessary in Oracle 12.2 provided the source database is in archivelog mode.
Switch to the local server and create a "tnsnames.ora" entry pointing to the remote database for use in the USING clause of the database link.
DB12C =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = my-server.my-domain)(PORT = 1521))
    )
    (CONNECT_DATA =
      (SERVICE_NAME = db12c)
    )
  )
Connect to the local database to initiate the clone.
export ORAENV_ASK=NO
export ORACLE_SID=cdb1
. oraenv
export ORAENV_ASK=YES

sqlplus / as sysdba
Create a database link in the local database, pointing to the remote database.
DROP DATABASE LINK clone_link;

CREATE DATABASE LINK clone_link
  CONNECT TO remote_clone_user IDENTIFIED BY remote_clone_user USING 'db12c';

-- Test link.
DESC user_tables@clone_link
Create a new PDB in the local database by cloning the remote non-CDB. In this case we are using Oracle Managed Files (OMF), so we don't need to bother with FILE_NAME_CONVERT parameter for file name conversions. Since there is no PDB to name, we use "NON$CDB" as the PDB name.
CREATE PLUGGABLE DATABASE db12cpdb FROM NON$CDB@clone_link;
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$pdbs WHERE name = 'DB12CPDB';
NAME OPEN_MODE
DB12CPDB MOUNTED
------------------------------ ----------
SQL>
Since this PDB was created as a clone of a non-CDB, before it can be opened we need to run the "$ORACLE_HOME/rdbms/admin/noncdb_to_pdb.sql" script to clean it up.
ALTER SESSION SET CONTAINER=db12cpdb;
@$ORACLE_HOME/rdbms/admin/noncdb_to_pdb.sql
The PDB can now be opened in read-write mode.
ALTER PLUGGABLE DATABASE db12cpdb OPEN;
SELECT name, open_mode FROM v$pdbs WHERE name = 'DB12CPDB';
NAME OPEN_MODE
DB12CPDB READ WRITE
------------------------------ ----------
SQL>
As with any PDB clone, check common users and the temporary tablespace is configured as expected.