ora
(known generically as init.ora or a PFILE) or a server parameter file (otherwise known as an
SPFILE). The instance first looks for an SPFILE in the default location for the operating system
($ORACLE_HOME/dbs on Unix, for example) as either spfile
.ora or spfile.ora. If neither
of these files exists, the instance looks for a PFILE with the name init.ora. Alternatively, the
startup command can explicitly specify a PFILE to use for startup.
Initialization parameter files, regardless of the format, specify file locations for trace files,
control files, filled redo log files, and so forth. They also set limits on the sizes of the various
structures in the System Global Area (SGA) as well as how many users can connect to the
database simultaneously.
Until Oracle9i, using the init.ora file was the only way to specify initialization parameters
for the instance. Although it is easy to edit with a text editor, it has some drawbacks. If a dynamic
system parameter is changed at the command line with the alter system command, the DBA must
remember to change the init.ora file so that the new parameter value will be in effect the next
time the instance is restarted.
An SPFILE makes parameter management easier and more effective for the DBA. If an SPFILE
is in use for the running instance, any alter system command that changes an initialization
28 Oracle Database 11g DBA Handbook
parameter can change the initialization parameter automatically in the SPFILE, change it only for
the running instance, or both.
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