Oracle Database Control

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 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$bgprocesses;
Log file locations	# display background (alert.log destination), core and user destinations show parameter dump_dest;