As per Oracle 12c documentation,  a PDB can

– have its own local temporary tablespace, or

– if it does not have its own  temporary tablespace, it can share the temporary tablespace with the CDB.

To demonstrate a PDB sharing the temporary tablespace of CDB,  the  first step is to create a PDB without a temporary tablespace. By default when a PDB is created from seed, it is created with its local temporary tablespace TEMP and it cannot be dropped as it is the default temporary tablespace of the PDB.

So, the only options I could think of were to

Method – I

• Create a non-CDB without temporary tablespace and the plug it into a CDB

Method – II

• Create a non-CDB / PDB with temporary tablespace,
• Generate its xml file using dbms_PDB
•  Edit the xml file to remove the entry for temporary tablespace
•   Plug in the non-CDB into a CDB

I will demonstrate the second method. For this purpose, I created a non-CDB orcl2 using DBCA so that it contained default temporary tablespace temp.

– Open the non-CDB in read only mode

ORCL2> shu immediate;
             startup mount;
             alter database open read only;

– Generate an XML metadata file for the non-CDB

ORCL2>exec dbms_pdb.describe ('/u01/app/oracle/oradata/orcl2/orcl2.xml');

– Edit the xml file to remove the entry for temp tablespace

[oracle@em12 ~]$ vi /u01/app/oracle/oradata/orcl2/orcl2.xml

– Use the xml file to plug in the non-CDB into  CDB2 as PDB_ORCL2

CDB$ROOT@CDB2>create pluggable database pdb_orcl2 using '/u01/app/oracle/oradata/orcl2/orcl2.xml'  nocopy;

– Connect to PDB_ORCL2 and run the “$ORACLE_HOME/rdbms/admin/noncdb_to_pdb.sql” script to clean up the new PDB, removing any items that should not be present in a PDB.

CDB$ROOT@CDB2>connect sys/oracle@pdb_orcl2 as sysdba

PDB_ORCL2@CDB2> @?/rdbms/admin/noncdb_to_pdb

PDB_ORCL2@CDB2> alter pluggable database open;

– Check that data from non-CDB is available in the new PDB

PDB_ORCL2@CDB2>select count(empno) from scott.emp;

COUNT(EMPNO)
------------
14

– Verify that temporary tablespace has not been created in PDB_ORCL2

PDB_ORCL2@CDB2> select tablespace_name from dba_tablespaces;

TABLESPACE_NAME
------------------------------
SYSTEM
SYSAUX
USERS
EXAMPLE

– Verify that tempfile has not been created in PDB_ORCL2

PDB_ORCL2@CDB2> select name from v$tempfile;

no rows selected

So, I was able to create a PDB without temporary tablespace. Now I wanted to check if PDB_ORCL2 uses the temp tablespace of the CDB.

– First check that default temporary tablespace TEMP exists for the CDB

CDB$ROOT@CDB2> select tablespace_name from dba_tablespaces;

TABLESPACE_NAME
------------------------------
SYSTEM
SYSAUX
UNDOTBS1
TEMP
USERS

CDB$ROOT@CDB2>  select PROPERTY_NAME, PROPERTY_VALUE

from database_properties
where upper(PROPERTY_NAME) like '%TEMP%';

PROPERTY_NAME                  PROPERTY_VALUE
------------------------------ ---------------
DEFAULT_TEMP_TABLESPACE        TEMP

– Set pga_aggregate_target to its lowest allowed value of 10m to force a sort to spill to the temporary tablespace.

 CDB$ROOT@CDB2> alter system set pga_aggregate_target=10m;

– Issue a query in PDB_ORCL2 which will spill to temporary tablespace

PDB_ORCL2@CDB2> select * from dba_objects order by 1,2,3,4,5,6,7;
select * from dba_objects order by 1,2,3,4,5,6,7
*
ERROR at line 1:
ORA-00959: tablespace 'TEMP' does not exist

I expected the query to use temporary tablespace TEMP of CDB but it failed as it expected temp tablespace to exist locally for PDB as its default temporary tablespace is set to TEMP (as was in non-CDB)

PDB_ORCL2@CDB2> col property_name for a30
PDB_ORCL2@CDB2> col property_value for a15
PDB_ORCL2@CDB2> l
1  select PROPERTY_NAME, PROPERTY_VALUE from database_properties
2*  where upper(PROPERTY_NAME) like '%TEMP%'
PDB_ORCL2@CDB2> /

PROPERTY_NAME                  PROPERTY_VALUE
------------------------------ ---------------
DEFAULT_TEMP_TABLESPACE        TEMP

 — I tried to modify the default temporary tablespace to cdb$root:temp but that attempt also failed.

PDB_ORCL2@CDB2> alter database default temporary tablespace cdb$root:temp;
alter database default temporary tablespace cdb$root:temp
*
ERROR at line 1:
ORA-00933: SQL command not properly ended

Hence, I was able to create a PDB without temporary tablespace but could not make it use the temporary tablespace of CDB.

References:

Oracle documentation

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Related Links:

Home

Database 12c Index

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In Oracle 12c, you can connect to a PDB using two methods :

– Switch the container using Alter system set container …

– Use connect command to connect to PDB using network alias

Let’s compare the two methods :

The use of SET CONTAINER avoids the need to create a new connection from scratch.

If there is an existing connection to a PDB / CDB$root, the same connection can be used to connect to desired PDB / CDB$root.

– Connect to CDB

[oracle@em12 ~]$ sqlplus system/oracle@cdb1

CDB$ROOT@CDB1> sho con_name

CON_NAME
------------------------------
CDB$ROOT

– Check the PID for the process created on the operating system

[oracle@em12 ~]$ ps -ef |grep LOCAL |grep -v grep

oracle 23271 1 0 10:23 ? 00:00:00 oraclecdb1 (LOCAL=NO)

– Change the container to PDB1 using Set container

CDB$ROOT@CDB1> alter session set container=pdb1;

sho con_name

CON_NAME
------------------------------
PDB1

– Check that the operating system PID remains the same as earlier connection is reused and a new connection has not been created

[oracle@em12 ~]$ ps -ef |grep LOCAL |grep -v grep

oracle 23271 1 0 10:23 ? 00:00:00 oraclecdb1 (LOCAL=NO)

– Switch the container back to cdb$root using connect

CDB$ROOT@CDB1> conn system/oracle@cdb1
sho con_name

CON_NAME
------------------------------
CDB$ROOT

– Check that a new operating system PID has been created as a new  connection  has been created

[oracle@em12 ~]$ ps -ef |grep LOCAL |grep -v grep

oracle 23409 1 0 10:29 ? 00:00:00 oraclecdb1 (LOCAL=NO)

glogin.sql is not executed when Alter session set container is used

To demonstrate it, I have added following lines to my glogin.sql to display CDB/PDB name in SQL prompt:

define gname=idle
column global_name new_value gname
set heading off
set termout off
col global_name noprint
select upper(sys_context ('userenv', 'con_name') || '@' || sys_context('userenv', 'db_name')) global_name from dual;
set sqlprompt '&gname> '
set heading on
set termout on

- Let’s connect to PDB1 using “Connect” and verify that glogin.sql is executed and prompt displays CDB/PDB name

 

SQL> conn sys/oracle@pdb1 as sysdba
PDB1@CDB1> 

- Verify that the prompt displays current container (PDB1) and container database (CDB1)

PDB1@CDB1> sho con_name
PDB1

PDB1@CDB1> sho parameter db_name
db_name                              string      cdb1

– Now let’s connect to PDB2 using Alter session set container and verify that glogin.sql is not executed and the same prompt as earlier is displayed

PDB1@CDB1>  alter session set container=pdb2;

 Session altered.

PDB1@CDB1> sho con_name

CON_NAME

 ------------------------------

 PDB2  

-- Let's connect to PDB2 using connect and verify that glogin.sql is executed as the prompt displays the PDB name PDB2

 PDB1@CDB1> connect sys/oracle@pdb2 as sysdba

 PDB2@CDB1> 

Pending transactions are not committed when Alter system set container is used

– Let’s start a transaction in PDB1

PDB1@CDB1> create table pdb1_tab(x number);

Table created.

PDB1@CDB1> insert into pdb1_tab values (1);

1 row created.

– Switch the container to PDB2

PDB1@CDB1> alter session set container=pdb2;

– Try to start another transaction on PDB2 – does not allow as an active transaction exists in the parent container PDB1

PDB1@CDB1> create table pdb2_tab (x number);

 create table pdb2_tab (x number)

 *

 ERROR at line 1:

 ORA-65023: active transaction exists in container PDB1

– In another session check that the transaction was not committed and no rows are visible in table pdb1_tab

CDB$ROOT@CDB1> conn system/oracle@pdb1

 PDB1@CDB1> select * from pdb1_tab;

no rows selected

 Alter session set container cannot be used by local users

 

– Try to give set container privilege to a local user HR in PDB2 – fails as common privilege cannot be granted to a local user and hence a local user cannot user alter session set container to connect to another PDB

PDB2@CDB1> connect system/oracle@pdb2

 PDB2@CDB1> grant set container to hr container=all;

 grant set container to hr container=all

 *

 ERROR at line 1:

 ORA-65030: one may not grant a Common Privilege to a Local User or Role

I hope this post was useful.

Your comments and suggestions are always welcome.

References :

http://docs.oracle.com/cd/E16655_01/server.121/e17636/cdb_admin.htm#ADMIN13970

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Related Links:

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Database 12c Index

12c : Connecting To PDB’s With Same Name
12c: USE_SID_AS_SERVICE_listener_name

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