Oracle Database Admin (DBA) Tutorial: Startup and shutdown

Startup Modes:-

1. Nomount:- This command starts the instance, but leaves the database dismounted and closed. 
2. Mount:- The instance is started and is associated with a database by reading its control file. The database is closed to users.
3. Open:- The instance is started and is associated with an open database. The data contained in the data files is accessible to authorized users.
4. Startup force:- The startup force option internally shuts down the database and restarts it.

Shutdown Modes:-

1. Shutdown Abort:- This mode is intended for emergency situations, such as when no other form of shutdown is successful. This mode of shutdown is the fastest. However, a subsequent open of this database may take substantially longer because instance recovery must be performed to make the data files consistent.
2. Shutdown Immediate:- This mode is typically the fastest next to SHUTDOWN ABORT. Oracle Database terminates any executing SQL statements and disconnects users. Active transactions are terminated and uncommitted changes are rolled back.
3. Shutdown Transactional:- This mode prevents users from starting new transactions, but waits for all current transactions to complete before shutting down. This mode can take a significant amount of time depending on the nature of the current transactions.
4. Shutdown Normal:- This is the default mode of shutdown. The database waits for all connected users to disconnect before shutting down.