4-21. Oracle Database Instance states

Oracle DB can be in one of the following states:

1. SHUTDOWN
2. NOMOUNT (instance started): An instance is typically started only in NOMOUNT mode during database creation, during re-creation of control files, or during certain backup and recovery scenarios.
3. MOUNT (control file opened for this instance): here the data files and online redo log files are NOT opened so specific maintenance tasks can be performed such as 1) renaming data files (though data files on an offline tablespace can be renamed while the db is open), 2) enabling and disabling online redo log file archiving options, 3) perfoming full database recovery, etc.
   Note: a database may be left in MOUNT mode even thoug an OPEN request has been made. This may be because the database needs to be recovered in some way.
4. OPEN: this includes opening the online data files and the redo log files.

You can also start up a database instance in restricted mode so that it is available to users with administrative privileges only. to start an instance in restricted mode, select the "Restrict access to database" option on the Advanced Startup Options page.

Starting an instance includes the following tasks:

• Searching /database for a file of a particular name in this order:
• • spfile.ora
  • If not found, spfile.ora
  • If not found, init.oraThis is the file that contains initialization parameters for the instance. Specifying the PFILE parameter with STARTUP overrides the default behavior.
• Allocating the SGA
• Starting the background processes
• Opening the alert.log file and the trace files