File name: initSID.ora
Location: $ORACLE_HOME/dbs

The Oracle Universal Installer creates a sample init.ora file.
Copy and use the sample file is allowed to configure specific database initialization parameters.

Initialization parameter in the iniSID.ora file:

- Name of database and parameters associated with database, system Global Area Parameters, action to do when the log files are full, specify the name and location of the control files and more information about undo segments.

Database parameters: eg. db_block_size 
Memory parameters: shared_pool_size, db_block_buffers, hash_area_size, sort_area_size,
Parallel Query parameters: parallel_threads_per_cpu
Optimizer and query parameters: optimizer_mode
IO parameters: db_file_multiblock_read_count
Materialized view parameters: query_rewrite_enabled
Other Parameters: db_name, control_files


Creating the SPFILE – from the PFILE

The spfile or spdileSID.ora is a binary persistent file maintained by the Oracle Server and can not be updated manually, even is the file is changed manually it becomes useless.

File name: spfileSID.ora
Location: $ORACLE_HOME/dbs

To create the spfile from the pfile can execute the command with SYSDBA privileges:

CREATE SPFILE FROM PFILE;

With file names specification:
CREATE SPFILE = ‘spfile file-name’ FROM PFILE=’pfile filename’;

Optional, the spfile can be created using Enterprise Manager: Instance / Configuration / Select Object / Create spfile from main menu

How to check the current  SGA setting values


1. Connect to the database using SQL*plus  

COMMAND:

SQL> select * from v$sga;

NAME VALUE
-------------------- ----------
Fixed Size               75804
Variable Size           387203072
Database Buffers     1084170240
Redo Buffers           499712