Oracle Database Administration

Database files

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

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

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

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

Control files• Control file contains:

– 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

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)

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

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)

Example parameter fileimm.__db_cache_size=138412032imm.__java_pool_size=4194304imm.__large_pool_size=4194304imm.__shared_pool_size=58720256imm.__streams_pool_size=0*.audit_file_dest='C:\oracle\admin\imm\adump'*.background_dump_dest='C:\oracle\admin\imm\bdump'*.compatible='10.2.0.1.0'*.control_files='C:\oracle\oradata\imm\control01.ctl','C:\oracle\oradata\

imm\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=2147483648*.job_queue_processes=10*.nls_language='AMERICAN'*.nls_territory='POLAND'*.open_cursors=300*.pga_aggregate_target=69206016*.processes=150*.remote_login_passwordfile='EXCLUSIVE'

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)

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

Adjusting database parameters• When using PFILE – modify the text file and

restart the database• When using SPFILE:

– alter system set db_cache_size = 30000000 scope=memory;

– alter system set db_cache_size = 30000000 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