12c: Connecting to CDB/PDB – Set Container Vs Connect

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:

Home

Database 12c Index

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

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Your comments and suggestions are welcome!