The database administrator can adjust variable parameters to improve the
performance of a database system. Exactly which parameters most affect a system
depends on numerous database characteristics and variables.

Some parameters can be changed dynamically with the ALTER SESSION or ALTER
SYSTEM statement while the instance is running. Unless you are using a server
parameter file (SPFILE), changes made using the ALTER SYSTEM statement are only
in effect for the current instance. You must manually update the text initialization
parameter file for the changes to be known the next time you start up an instance.
When you use a SPFILE, you can update the parameters on disk, so that changes
persist across database shutdown and startup.

Oracle provides values in the starter initialization parameter file provided with your
database software, or as created for you by the Database Configuration Assistant. You
can edit these Oracle-supplied initialization parameters and add others, depending
upon your configuration and options and how you plan to tune the database. For any
relevant initialization parameters not specifically included in the initialization
parameter file, Oracle supplies defaults. If you are creating an Oracle database for the
first time, it is suggested that you minimize the number of parameter values that you
alter.