Shutting Down with the IMMEDIATE Option
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Use immediate database shutdown only in the following situations:

A power shutdown is going to occur soon.

The database or one of its applications is functioning irregularly.

Immediate database shutdown proceeds with the following conditions:

Any uncommitted transactions are rolled back. (If long uncommitted transactions exist, this method of shutdown might not complete quickly, despite its name.)

Oracle does not wait for users currently connected to the database to disconnect; Oracle implicitly rolls back active transactions and disconnects all connected users.

The next startup of the database will not require any instance recovery procedures.

To shut down a database immediately, use the SHUTDOWN command with the IMMEDIATE option

SHUTDOWN IMMEDIATE;



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Note:
The SHUTDOWN IMMEDIATE statement disconnects all existing idle connections and shuts down the database. If, however, you have submitted processes (for example, inserts, selects or updates) that are awaiting results, the SHUTDOWN TRANSACTIONAL statement allows the process to complete before disconnecting.
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Shutting Down with the ABORT Option
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You can shut down a database instantaneously by aborting the database's instance. If possible, perform this type of shutdown only in the following situations:

The database or one of its applications is functioning irregularly and neither of the other types of shutdown works.

You need to shut down the database instantaneously (for example, if you know a power shutdown is going to occur in one minute).

You experience problems when starting a database instance.

Aborting an instance shuts down a database and yields the following results:

Current client SQL statements being processed by Oracle are immediately terminated.

Uncommitted transactions are not rolled back.

Oracle does not wait for users currently connected to the database to disconnect; Oracle implicitly disconnects all connected users.

The next startup of the database will require instance recovery procedures.

If both the normal and immediate shutdown options do not work, abort the current database instance immediately by issuing the SHUTDOWN command with the ABORT option:

SHUTDOWN ABORT;