Initialization Parameter files: PFILEs vs. SPFILEs【转】

Initialization Parameter files: PFILEs vs. SPFILEs

Submitted by admin on Sun, 2003-08-03 19:29 

source link：http://www.orafaq.com/node/5

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:

• An SPFILE can be backed-up with RMAN (RMAN cannot backup PFILEs)
• Reduce human errors. The SPFILE is maintained by the server. Parameters are checked before changes are accepted.
• Eliminate configuration problems (no need to have a local PFILE if you want to start Oracle from a remote machine)
• 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.

Viewing Parameters Settings:

One can view parameter values using one of the following methods (regardless if they were set via PFILE or SPFILE):

• The "SHOW PARAMETERS" command from SQL*Plus (i.e.: SHOW PARAMETERS timed_statistics)
• V$PARAMETER view - display the currently in effect parameter values
• V$PARAMETER2 view - display the currently in effect parameter values, but "List Values" are shown in multiple rows
• V$SPPARAMETER view - display the current contents of the server parameter file.

Starting a database with a PFILE or SPFILE:

Oracle searches for a suitable initialization parameter file in the following order:

• Try to use the spfile${ORACLE_SID}.ora file in $ORACLE_HOME/dbs (Unix) or ORACLE_HOME/database (Windows)
• Try to use the spfile.ora file in $ORACLE_HOME/dbs (Unix) or ORACLE_HOME/database (Windows)
• Try to use the init${ORACLE_SID}.ora file in $ORACLE_HOME/dbs (Unix) or ORACLE_HOME/database (Windows)

One can override the default location by specifying the PFILE parameter at database startup:

SQL> STARTUP PFILE='/oradata/spfileORCL.ora'

Note that there is not an equivalent "STARTUP SPFILE=" command. One can only use the above option with SPFILE's if the PFILE you point to (in the example above), contains a single 'SPFILE=' parameter pointing to the SPFILE that should be used. Example:

SPFILE=/path/to/spfile

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='*';

The SCOPE parameter can be set to SPFILE, MEMORY or BOTH:

- MEMORY: Set for the current instance only. This is the default behaviour if a PFILE was used at STARTUP.

- SPFILE: update the SPFILE, the parameter will take effect with next database startup

- BOTH: affect the current instance and persist to the SPFILE. This is the default behaviour if an SPFILE was used at STARTUP.
The COMMENT parameter (optional) specifies a user remark.

The SID parameter (optional; only used with RAC) indicates the instance for which the parameter applies (Default is *: all Instances).

Use the following syntax to set parameters that take multiple (a list of) values:

SQL> ALTER SYSTEM SET utl_file_dir='/tmp/','/oradata','/home/' SCOPE=SPFILE;

Use this syntax to set unsupported initialization parameters (obviously only when Oracle Support instructs you to set it):

SQL> ALTER SYSTEM SET "_allow_read_only_corruption"=TRUE SCOPE=SPFILE;

Execute one of the following command to remove a parameter from the SPFILE:

SQL> ALTER SYSTEM RESET timed_statistics SCOPE=SPFILE SID=‘*’;
SQL> ALTER SYSTEM SET timed_statistics = '' SCOPE=SPFILE;

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:

• Export the SPFILE with: CREATE PFILE=‘pfilename’ FROM SPFILE = ‘spfilename’;
• Edit the resulting PFILE with a text editor
• Shutdown and startup the database with the PFILE option: STARTUP PFILE=filename
• Recreate the SPFILE with: CREATE SPFILE=‘spfilename’ FROM PFILE=‘pfilename’;
• 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;

References:

• Oracle9i Database Administrator's Guide Release 2 (9.2)
  Chapter 2: Creating an Oracle Database
• Oracle9i Recovery Manager User's Guide Release 2 (9.2)
  Chapter 5: "RMAN Concepts I: Channels, Backups, and Copies"
• Oracle9i SQL Reference Release 2 (9.2)