ORACLE : Initialization Parameter files: PFILEs vs. SPFILEs

When an Oracle Instance is started, the characteristics of the Instance are established by parameters specified within the initialization parameter file. These initialization parameters are either stored in a PFILE or SPFILE. SPFILEs are available in Oracle 9i and above. All prior releases of Oracle are using PFILEs.

SPFILEs provide the following advantages over PFILEs:
o An SPFILE can be backed-up with RMAN (RMAN cannot backup PFILEs)
o Reduce human errors. The SPFILE is maintained by the server. Parameters are checked before changes are accepted.
o Eliminate configuration problems (no need to have a local PFILE if you want to start Oracle from a remote machine)
o Easy to find - stored in a central location

What is the difference between a PFILE and SPFILE?
A PFILE is a static, client-side text file that must be updated with a standard text editor like "notepad" or "vi". This file normally reside on the server, however, you need a local copy if you want to start Oracle from a remote machine. DBA's commonly refer to this file as the INIT.ORA file.
An SPFILE (Server Parameter File), on the other hand, is a persistent server-side binary file that can only be modified with the "ALTER SYSTEM SET" command. This means you no longer need a local copy of the pfile to start the database from a remote machine. Editing an SPFILE will corrupt it, and you will not be able to start your database anymore.

How will I know if my database is using a PFILE or SPFILE?
Execute the following query to see if your database was started with a PFILE or SPFILE:
SQL> SELECT DECODE(value, NULL, 'PFILE', 'SPFILE') "Init File Type"
FROM sys.v_$parameter WHERE name = 'spfile';

You can also use the V$SPPARAMETER view to check if you are using a PFILE or not: if the "value" column is NULL for all parameters, you are using a PFILE.


Changing SPFILE parameter values:
While a PFILE can be edited with any text editor, the SPFILE is a binary file. The "ALTER SYSTEM SET" and "ALTER SYSTEM RESET" commands can be used to change parameter values in an SPFILE. Look at these examples:
SQL> ALTER SYSTEM SET open_cursors=300 SCOPE=SPFILE;

SQL> ALTER SYSTEM SET timed_statistics=TRUE
COMMENT='Changed by Frank on 1 June 2003'
SCOPE=BOTH
SID='*';


Converting between PFILES and SPFILES:
One can easily migrate from a PFILE to SPFILE or vice versa. Execute the following commands from a user with SYSDBA or SYSOPER privileges:
SQL> CREATE PFILE FROM SPFILE;
SQL> CREATE SPFILE FROM PFILE;
One can also specify a non-default location for either (or both) the PFILE and SPFILE parameters. Look at this example:
SQL> CREATE SPFILE='/oradata/spfileORCL.ora' from PFILE='/oradata/initORCL.ora';
Here is an alternative procedure for changing SPFILE parameter values using the above method:
o Export the SPFILE with: CREATE PFILE=‘pfilename’ FROM SPFILE = ‘spfilename’;
o Edit the resulting PFILE with a text editor
o Shutdown and startup the database with the PFILE option: STARTUP PFILE=filename
o Recreate the SPFILE with: CREATE SPFILE=‘spfilename’ FROM PFILE=‘pfilename’;
o On the next startup, use STARTUP without the PFILE parameter and the new SPFILE will be used.

Parameter File Backups:
RMAN (Oracle's Recovery Manager) will backup the SPFILE with the database control file if setting "CONFIGURE CONTROLFILE AUTOBACKUP" is ON (the default is OFF).

PFILEs cannot be backed-up with RMAN. Look at this example:
RMAN> CONFIGURE CONTROLFILE AUTOBACKUP ON;

Use the following RMAN command to restore an SPFILE:
RMAN> RESTORE CONTROLFILE FROM AUTOBACKUP;