Thursday, 18 May 2017

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

In 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.


Oracle DB PDB, Oracle Database 12c

  • Prerequisites

The prerequisites for cloning a remote PDB or non-CDB are very similar, so I will deal with them together.
  1. The user in the local database must have the CREATE PLUGGABLE DATABASE privilege in the root container.
  2. The remote CDB must use local undo mode. Without this you must open the remote PDB or non-CDB in read-only mode.
  3. The remote database should be in archivelog mode. Without this you must open the remote PDB or non-CDB in read-only mode.
  4. 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.
  5. The user in the remote database that the database link connects to must have the CREATE PLUGGABLE DATABASE privilege.
  6. The local and remote databases must have the same endianness.
  7. 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.
  8. 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.
  9. 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.
  10. 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).
  11. When cloning from a non-CDB, both the the local and remote databases must using version 12.1.0.2 or higher.
In the examples below I have three databases running on the same virtual machine, but they could be running on separate physical or virtual servers.
  1. cdb1 : The local database that will eventually house the clones.
  2. db12c : The remote non-CDB.
  3. 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 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_CONVERT parameter 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.
  • Appendix

These tests were performed on a free trial of the Oracle Database Cloud Service, where the CDB1 instance and PDB1 pluggable database were created as part of the service creation. The additional instances were built on the same virtual machine using the commands below. I've included the DBCA commands to create and delete the CDB1 instance for completeness. They were not actually used.

# Empty local container (cdb1).
dbca -silent -createDatabase \
 -templateName General_Purpose.dbc \
 -gdbname cdb1 -sid cdb1 -responseFile NO_VALUE \
 -characterSet AL32UTF8 \
 -sysPassword OraPasswd1 \
 -systemPassword OraPasswd1 \
 -createAsContainerDatabase true \
 -numberOfPDBs 1 \
 -pdbName pdb1 \
 -pdbAdminPassword OraPasswd1 \
 -databaseType MULTIPURPOSE \
 -automaticMemoryManagement false \
 -totalMemory 2048 \
 -storageType FS \
 -datafileDestination "/u01/app/oracle/oradata/" \
 -redoLogFileSize 50 \
 -initParams encrypt_new_tablespaces=DDL \
 -emConfiguration NONE \
 -ignorePreReqs

# Remote container (cdb3) with PDB (pdb5).
dbca -silent -createDatabase \
 -templateName General_Purpose.dbc \
 -gdbname cdb3 -sid cdb3 -responseFile NO_VALUE \
 -characterSet AL32UTF8 \
 -sysPassword OraPasswd1 \
 -systemPassword OraPasswd1 \
 -createAsContainerDatabase true \
 -numberOfPDBs 1 \
 -pdbName pdb5 \
 -pdbAdminPassword OraPasswd1 \
 -databaseType MULTIPURPOSE \
 -automaticMemoryManagement false \
 -totalMemory 2048 \
 -storageType FS \
 -datafileDestination "/u01/app/oracle/oradata/" \
 -redoLogFileSize 50 \
 -initParams encrypt_new_tablespaces=DDL \
 -emConfiguration NONE \
 -ignorePreReqs

# Non-CDB instance (db12c).
dbca -silent -createDatabase \
 -templateName General_Purpose.dbc \
 -gdbname db12c -sid db12c -responseFile NO_VALUE \
 -characterSet AL32UTF8 \
 -sysPassword OraPasswd1 \
 -systemPassword OraPasswd1 \
 -createAsContainerDatabase false \
 -databaseType MULTIPURPOSE \
 -automaticMemoryManagement false \
 -totalMemory 2048 \
 -storageType FS \
 -datafileDestination "/u01/app/oracle/oradata/" \
 -redoLogFileSize 50 \
 -initParams encrypt_new_tablespaces=DDL \
 -emConfiguration NONE \
 -ignorePreReqs

# Delete the instances.
#dbca -silent -deleteDatabase -sourceDB cdb1 -sysDBAUserName sys -sysDBAPassword OraPasswd1
dbca -silent -deleteDatabase -sourceDB cdb3 -sysDBAUserName sys -sysDBAPassword OraPasswd1
dbca -silent -deleteDatabase -sourceDB db12c -sysDBAUserName sys -sysDBAPassword OraPasswd1

As explained earlier, in all cases Oracle Managed Files (OMF) was used so no file name conversions were needed. Also, the source databases were switched to archivelog mode.

export ORAENV_ASK=NO
export ORACLE_SID=cdb3
. oraenv
export ORAENV_ASK=YES

sqlplus / as sysdba <<EOF

ALTER SYSTEM SET db_create_file_dest = '/u01/app/oracle/oradata';

SHUTDOWN IMMEDIATE;
STARTUP MOUNT;
ALTER DATABASE ARCHIVELOG;
ALTER DATABASE OPEN;

ALTER PLUGGABLE DATABASE pdb5 OPEN;
ALTER PLUGGABLE DATABASE pdb5 SAVE STATE;

EXIT;
EOF