Oracle Database Control

When Oracle starts it goes through 3 stages which are

Startup (nomount) Oracle first reads the parameter file (pfile or spfile) and obtains all memory parameters in order to configure the SGA, memory allocatations take place and the necessary background processes are started. Remember the Memory allocation with the background processes is called the INSTANCE.
Mount At this stage Oracle opens and reads the controlfile and obtains the location of the datafiles but it does not open them.
Open The last stage is to open the datafiles (also called the DATABASE) for reading and writing, Oracle makes sure that the datafiles are consistent.

Startup

Nomount Mode startup nomount;

Note: The INSTANCE is born, memory allocated and background processes started but the controlfile has not been read and the datafiles are not open for reading or writing
Mount Mode

startup mount;

Note: The controlfile has been read at this stage but the datafiles are not open for reading or writing.

Read Only Mode

startup open read only

Note: the database files are open for reading only

Open Mode startup
startup open

Note: database files will be open for reading and writing, this is the normal mode of operation.
Force mode

startup force;

Note: this performs a 'shutdown abort' followed by a 'startup'

Restricted Mode

startup restrict;

# To change into restricted mode
alter system enable restricted session;
alter system disable restricted session;

Note: Users with restricted access can access the system only (normally DBA's)
Alter operation mode

# You must be in mount mode to alter the database, if not then shutdown the database first

alter database mount;
alter database open;
alter database open read only;
alter database restricted;

Display operation mode

# Display instance state in nomount mode v$database is unavailable.
# MODES:
#   started (nomount mode)
#   mounted (mount mode)
#   open (open mode)

select status from v$instance;

# Obtain the database operation mode, the database must be in mounted or open mode to access v$database
# MODES:
#   mounted (mount mode)
#   read write (open mode)
#   read only (open mode)

select open_mode from v$database;

# Is restricted session enabled
select logins from v$instance;

Parameter File

As stated in the Oracle structure web page, Oracle can access two types of parameter file pfile (text based) or spfile (binary based), you can specify which parameter you want to start the database with

pfile startup pfile='c:\oracle\pfiles\initD10.ora'
spfile # There is no option to specify a spfile but you can use the pfile option and in the pfile # point to the spfile
Display the parameter file in use select name, value from v$parameter where name = 'spfile';
show parameter spfile;

For more information on Oracle's parameter file see Oracle Structure.

Shutdown

Oracle has a number of options to shutdown the database, there are four to choose from

Normal

No new connections
Will wait until all users have disconnected

Note: you could be waiting a long time, not normally used

Transactional

No new connections or transactions
Once all transactions have finished disconnect the client

Note: again you could be waiting a long time

Immediate No new connections
Uncommitted transactins will be rolled back then disconnect the client

Note: normal shutdown command used
Abort

No new connections
Disconnect client immediately (no rolling back any transactions)

Note: last resort shutdown command, a automatic recovery will take place when you start the database
Shutdown Commands
Shutdown commands

shutdown normal;
shutdown transactional;
shutdown immediate;
shutdown abort;

startup force;

Note: 'startup force' will run a 'shutdown abort' immediately followed by a 'startup'

Display if shutdown is in progress select shutdown_pending from v$instance;

Restricted and Quiesce Modes

When you have problems on an Oracle database sometimes you would like the database fully running but allow only privilege users access (normally DBA's), Oracle offers two modes

Restricted

In this mode any users without the restricted privilege will not be allowed to connect to the database, however any users that are still connected will be allowed to use any DML/DDL.

Note: make sure all users are disconnected (need to kill their sessions) before changing the mode into restricted.
Quiesce

In this mode all users transactions are allowed to complete, once completed the user is unable to perform any DML/DDL commands (their sessions appear to freeze) but remain connected to the database. Users will be allowed to login but the session will again appear to freeze.

DBA's can perform any DML/DDL as normal, their sessions are unaffected, this also applies to users with the restricted session privilege.

Useful Commands
Restricted

alter system enable restricted session;
alter system disable restricted session;

select logins from v$instance;

Grant restricted privilege grant restricted session to <user>;
Quiesce alter system quiesce restricted;
alter system unquiesce;

select active_state from v$instance;

Basic Database Information

To obtain general database information the following can be used

Display Parameter file select name, value from v$parameter where name = 'spfile';
show parameter spfile;
Parameter settings select name, value, isdefault, isses_modifiable, issys_modifiable from v$parameter;
Instance state select status from v$instance;
Database operation mode select open_mode from v$database;
Shutdown pending select shutdown_pending from v$instance;
Restricted Session Mode select logins from v$instance;
Quiesce Mode select active_state from v$instance;
Oracle version select * from v$version;
select * from product_component_version;
Log Mode

select log_mode from v$database;
archive log list;

License info select * from v$license;
Database options select * from v$option;
Memory Info show sga
select * from v$sga;
select * from v$sgainfo;
select * from v$ssgastat;
Display controlfiles select * from v$controlfile;
select * from v$controlfile_record_section;
Display Oracle processes select * from v$bgprocess;
Log file locations # display background (alert.log destination), core and user destinations
show parameter dump_dest;