This may seem pretty basic, so I apologize!

Once I set a parameter in the 9i spfile, how do I "unset" it back to it's default value? I had SORT_AREA_SIZE set, but I want to use PGA_AGGREGATE_TARGET. I set the PGA parameter, and set SORT_AREA_SIZE back to what it says is the default value. But ISDEFAULT in v$parameter still says FALSE.

Any ideas?