There are several ways to enable instances:
STARTUP – or STARTUP OPEN turn the database into a full-fledged model.
STARTUP NOMOUNT – enable the base to load level SPFILE or SGA. In this mode, we restore the control file (CONTROLFILE) and re-duplex the database (target must be in nomount mode).
STARTUP MOUNT – enable the base to load level, eg Data files, repetition log files, or control file. In this mode, you can restore the database from the backup.
ALTER DATBASE MOUNT – command to enter database into MOUNT mode from NOMOUNT mode (note that we cannot open database directly from NOMOUNT mode).
ALTER DATABASE OPEN – to open the database from MOUNT mode (if we have NOMOUNT mode this command will not work, we must first go to MOUNT mode).
As a database administrator, we have the ability to disable instances in several ways:
SHUTDOWN IMMEDIATE – aborts all active sessions and then rolls back all unsaved transactions.
SHUTDOWN NORMAL – closes the database after all user sessions have ended.
SHUTDOWN TRANSACTIONAL – Closes the database after all active transactions have been completed, preventing the user from logging on to the new user database.
SHUTDOWN ABORT immediately closes the database (we only use it if we can not close the database using SHUTDOWN IMMEDIATE, and we must close it immediately, for example in case of a failure).
1. Disable the instance.
2. Run the instance in nomount mode.
3. Open an instance.
4. Run the instance in mount mode.