DanBrother的部落格

Oracle Database Startup Sequence:
Oracle database normally goes through three stages (nomount, mount, open)
to be available for users accessing it.


1. NOMOUNT Stage: ("startup nomount")
   the initialization parameter file (init.ora) is read , the memory areas (e.g. SGA /
   PGA) associated  with the database instance are allocated.
   the Oracle background processes (e.g. SMON / PMON) and Oracle instance started.
   The control file can be re-created during this stage.

SQL> select instance_name, status from v$instance;

INSTANCE_NAME STATUS
------------- ----------------------
TESTDB        STARTED

  
2. MOUNT Stage: ("startup mount" ;  "alter database mount" when db in nomount mode)
   the control file is read and Oracle determins the location of the datafiles.
   Archive / No Archive Log Mode can be changed during this stage.

SQL> select name, open_mode from v$database;

NAME      OPEN_MODE
---------       ----------------
TESTDB    MOUNTED

3. OPEN Stage: ("startup" ; "startup open" ; "alter database open" when db in mount mode)
   The datafiles and redo log files are checked for consistency and the database opened and all the datafiles are available for db users to access.
   
SQL> select name, open_mode from v$database;

NAME      OPEN_MODE
---------      ----------------------
TESTDB    READ WRITE