“Scope” is a parameter used for the alter system command when you are changing any initialization
parameter of an spfile. It is vital to understand how to use this parameter to achieve the desired effect.
The SCOPE parameter can take this three values MEMORY, SPFILE and BOTH.
Alter system set PARAMETER=VALUE SCOPE=SPFILE;
If you want to make a change to a parameter in the spfile without affecting the current instance, you can do so using the SCOPE=SPFILE option of the ALTER SYSTEM statement.
This is useful when you want to make a change starting from the next startup and not for the current instance.
Alter system set PARAMETER=VALUE SCOPE=MEMORY;
The SCOPE=MEMORY tells Oracle to make the change for the life of the instance,and to change it back to the default value the next time the database is bounced.
Alter system set PARAMETER=VALUE SCOPE=BOTH;
When you specify SCOPE=BOTH, the change will be made immediately, and Oracle will also make the change permanent, even after the database is bounced.