Apress.Expert.Oracle.Database.Architecture.9i.and.10g.Programming.Techniques.and.Solutions.Sep.2005

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CHAPTER 3 ■ FILES
Unsetting Values in SPFILEs
The next question that arises is, “OK, so we set a value, but we would now like to ‘unset’ it—in
other words, we don’t want that parameter setting in our SPFILE at all, and we would like it
removed. Since we cannot edit the file using a text editor, how do we accomplish that?” This,
too, is done via the ALTER SYSTEM command, but using the RESET clause:
Alter system reset parameter sid='sid|*'
Here the SCOPE/SID settings have the same meaning as before, but the SID= component is
not optional. The documentation in the Oracle SQL Reference manual is a bit misleading on
this particular command, as it seems to indicate that it is only valid for RAC (clustered) databases.
In fact, it states the following:
The alter_system_reset_clause is for use in a Real Application Clusters environment.
Later, it does go on to state
In a non-RAC environment, you can specify SID='*' for this clause.
But this is a bit confusing. Nonetheless, this is the command we would use to “remove” a
parameter setting from the SPFILE, allowing it to default. So, for example, if we wanted to
remove the SORT_AREA_SIZE, to allow it to assume the default value we specified previously,
we could do so as follows:
sys@ORA10G> alter system reset sort_area_size scope=spfile sid='*';
System altered.
The SORT_AREA_SIZE is removed from the SPFILE, a fact you can verify by issuing the
following:
sys@ORA10G> create pfile='/tmp/pfile.tst' from spfile;
File created.
You can then review the contents of /tmp/pfile.tst, which will be generated on the database
server. You will find the SORT_AREA_SIZE parameter does not exist in the parameter files
anymore.
Creating PFILEs from SPFILEs
The CREATE PFILE...FROM SPFILE command from the previous section is the opposite of
CREATE SPFILE. It takes the binary SPFILE and creates a plain text file from it—one that can be
edited in any text editor and subsequently used to start up the database. You might use this
command for at least two things on a regular basis:
• To create a “one-time” parameter file used to start up the database for maintenance, with
some special settings. So, you would issue CREATE PFILE...FROM SPFILE and edit the
resulting text PFILE, modifying the required settings. You would then start up the database,
using the PFILE= option to specify use of your PFILE instead of the
SPFILE. After you are finished, you would just start up normally, and the database