Parámetros de inicio en 12c cuando se utiliza arquitectura de bases de datos CDB/PDB (multitenant)

A text initialization parameter file (PFILE) cannot contain PDB-specific parameter values. 

A CDB uses an inheritance model for initialization parameters in which PDBs inherit initialization parameter values from the root. In this case, inheritance means that the value of a particular parameter in the root applies to a particular PDB.

A PDB can override the root's setting for some parameters, which means that a PDB has an inheritance property for each initialization parameter that is either true or false. The inheritance property is true for a parameter when the PDB inherits the root's value for the parameter. The inheritance property is false for a parameter when the PDB does not inherit the root's value for the parameter.

The inheritance property for some parameters must be true. For other parameters, you can change the inheritance property by running theALTER SYSTEM SET statement to set the parameter when the current container is the PDB. If ISPDB_MODIFIABLE is TRUE for an initialization parameter in the V$SYSTEM_PARAMETER view, then the inheritance property can be false for the parameter. When the current container is the root, the CONTAINER clause of the ALTER SYSTEM SET statement controls which PDBs inherit the parameter value being set.


The ALTER SYSTEM SET initialization_parameter statement can modify only some initialization parameters for PDBs. All initialization parameters can be set for the root. For any initialization parameter that is not set explicitly for a PDB, the PDB inherits the root's parameter value.

You can modify an initialization parameter for a PDB when the ISPDB_MODIFIABLE column is TRUE for the parameter in the V$SYSTEM_PARAMETERview. The following query lists all of the initialization parameters that are modifiable for a PDB: 

SELECT NAME FROM V$SYSTEM_PARAMETER WHERE ISPDB_MODIFIABLE='TRUE' ORDER BY NAME;

When the current container is a PDB, run the ALTER SYSTEM SET initialization_parameter statement to modify the PDB. The statement does not affect the root or other PDBs. When a PDB is unplugged from a CDB, the values of the initialization parameters that were specified for the PDB with SCOPE=BOTH orSCOPE=SPFILE are added to the PDB's XML metadata file. These values are restored for the PDB when it is plugged in to a CDB.

To make an underscore parameter persistent inside a 12c PDB, the same underscore parameter needs to be specified explicitly(with its default value) in cdb$root.
Until they are specified in root, they are not available to be modified in PDBs since this is a dictionary operation for PDBs.

References:

Documenation Links - 12c

Deprecated Parameters 12c
http://docs.oracle.com/cd/E16655_01/server.121/e17642/deprecated.htm#UPGRD60057

Using the ALTER SYSTEM SET Statement in a CDB in 12c 
http://docs.oracle.com/cd/E16655_01/server.121/e17636/cdb_admin.htm#ADMIN13650

Using the ALTER SYSTEM Statement to Modify a PDB in 12c
http://docs.oracle.com/cd/E16655_01/server.121/e17636/cdb_pdb_admin.htm#ADMIN13652