1. Oracle Database Administration
Database files

2. Database files Oracle Database uses the following types of files:
Data files
Control files
Redo log file (or just: Log files)
Archive log files
Parameter files

3. Database startup process
Database startup involves 3 steps:
Instance startup
PARAMETER FILE is read
Parameter file contains location of control file(s)
Mount database
CONTROL FILE is opened
Control File contains location of data files and log files
Open database
Data files and log files are opened

4. Data files Data files: all database data is stored there
data files can automatically extend if required (the AUTOEXTEND clause)
one or more datafile form a logical unit of database storage called a tablespace
Oracle does not write modified data immediately, if the database is not closed properly, the datafiles can contain incorrect data

5. Data files Data files: all database data is stored there
data files can automatically extend if required (the AUTOEXTEND clause)
one or more datafile form a logical unit of database storage called a tablespace
Oracle does not write modified data immediately, if the database is not closed properly, the datafiles can contain incorrect data

6. Control files Control file contains: Control file:
database name, timestamp of database creation
location of database datafiles and redo log files
system change number (SCN), every transaction increases SCN
Control file:
is modified every time there is structural change to the database (e.g. new datafile, redo log file)
is required for the database to operate
can be multiplexed
is used during database recovery

7. Redo log files Redo log files:
must be at least two, usually three or more
are written sequentially
record every change to the database
can be multiplexed
redo log files are used by recovery operations:
automatic recovery after instance failure (for example after SHUTDOWN ABORT), loss of a redo log file can prevent from opening the database
manual recovery from backup, loss of a redo log file can make it impossible to perform complete recovery (and some transactions will be lost)

8. Archive log files
Redo log files can be archived before they are overwritten, then they become archive log files
Archive log files:
are used by manual recovery only
can be multiplexed

9. Parameter files
Parameter file contains instance and database parameters, for example:
instance name
location of control files
database block size
amount of memory used by Oracle
Parameters can be stored in:
parameter file (regular text file)
server parameter file (binary file)

10. Example parameter file
imm.__db_cache_size=
imm.__java_pool_size=
imm.__large_pool_size=
imm.__shared_pool_size=
imm.__streams_pool_size=0
*.audit_file_dest='C:\oracle\admin\imm\adump'
*.background_dump_dest='C:\oracle\admin\imm\bdump'
*.compatible=' '
*.control_files='C:\oracle\oradata\imm\control01.ctl','C:\oracle\oradata\im m\control02.ctl','C:\oracle\oradata\imm\control03.ctl'
*.core_dump_dest='C:\oracle\admin\imm\cdump'
*.db_block_size=8192
*.db_domain=''
*.db_file_multiblock_read_count=16
*.db_name='imm'
*.db_recovery_file_dest='C:\oracle\flash_recovery_area'
*.db_recovery_file_dest_size=
*.job_queue_processes=10
*.nls_language='AMERICAN'
*.nls_territory='POLAND'
*.open_cursors=300
*.pga_aggregate_target=
*.processes=150
*.remote_login_passwordfile='EXCLUSIVE'

11. Parameter files Oracle can use PFILE or SPFILE
SPFILE can be modified by Oracle commands, PFILE must be modified manually
When using SPFILE:
some parameters can be changed while the database is running
Oracle can adjust some parameters automatically at runtime (e.g. memory distribution)

12. Using parameter files
Normally Oracle uses PFILE or SPFILE from default locations
It is possible to override default locations:
STARTUP PFILE=‘path_to_pfile.ora’
STARTUP SPFILE=‘path_to_spfile.ora’
It is possible to create PFILE from SPFILE and SPFILE from PFILE:
CREATE SPFILE FROM PFILE
CREATE PFILE FROM SPFILE
CREATE PFILE=‘path_to_pfile.ora’ FROM SPFILE

13. Adjusting database parameters
When using PFILE – modify the text file and restart the database
When using SPFILE:
alter system set db_cache_size = scope=memory;
alter system set db_cache_size = scope=spfile
Scope parameter can be:
memory – change the parameter immediately, do not write to spfile
spfile – write to spfile, do not change until restart
both – change immediately and write to spfile