Startup and shutdown of Oracle 12c database

(i) Launch of the database
Starting (startup) a database requires three steps.
1. Launch the Oralce instance
2. Loading the database by instance
3. Open the Database
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1) STARTUP Nomount
The Nomount option launches only one Oracle instance
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2) STARTUP MOUNT
The Startup Mount command launches the instance and mounts the database
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3) STARTUP
The startup command finishes launching the instance, loading the database, and opening the database
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If you use startup Nomount to open the database, you must use the ALTER DATABASE command to perform the mount and open the database operation must add the following command
STARTUP Nomount
ALTER DATABASE MOUNT
ALTER DATABASE OPEN
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If you open the database in startup MOUNT, you need to add the following command
STARTUP MOUNT
ALTER DATABASE OPEN
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(ii) Closure of the database
Close (SHUTDOWN) a database has four different shutdown options.
1) SHUTDOWN NORMAL
Executing shutdown normal is equivalent to performing shutdown
After the command is executed, any new users will no longer be allowed to connect to the database, and Oracle will wait for the connected user to shut down the database until the database is closed. In this way, shutting down the database does not require any instance recovery at the next boot.
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2) SHUTDOWN IMMEDIATE
This command is a common way of shutting down a database, which immediately interrupts the SOL statement that is being processed by Oracle. The system does not wait for all users connected to the database to exit the system, forcing it to roll back all currently active objects and then disconnect all connected users.
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3) SHUTDOWN transactional
This command is often used to schedule a shutdown of the database, he waits for the current connection to the system and the activity is completed, and any new connections and things are not allowed after the command is run. After all the active things are done, the database shuts down the database in the same way as shutdown immediate.
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4) SHUTDOWN ABORT
This command is the last choice to shut down the database, the method that has to be used when there is no way to shut down the database, generally do not use.
You can consider using the following conditions:
1. The database is in an unhealthy state and you cannot close the database using the SHUTDOWN normal or SHUTDOWN immediate command.
2. Need to close the database immediately
3. A problem occurred while restarting the DB instance
All running SQL statements will be terminated immediately, all uncommitted things will not be rolled, all users will be disconnected directly, and the next time the database is started, the instance recovery is required.
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Friendly Tips
It is best to use the shutdown immediate method when you close the database because it is safe and relatively fast. It is not a last resort to use the Shutdown Abort method, as this will result in data loss and a longer time to recover the database.

Startup and shutdown of Oracle 12c database