What is Row Level Lock in Oracle?

• Oracle automatically acquires locks which are row-level locks. A transaction can held no of row locks and oracle does not work on it.
• Row locking provides the lowest level of locking. It provides the best possible transaction concurrency.Readers of data do not wait for writers of the same data rows.  
• A modified row is always locked exclusively so that other users cannot modify the row until the transaction holding the lock is committed or rolled back.
• If a transaction obtains a row lock for a row, the transaction also acquires a table lock for the corresponding table. The table lock prevents conflicting DDL operations that would override data changes in a current transaction.
• A Transaction gets an exclusive DML row level lock for each row modified by any of the following statements: INSERT, UPDATE, DELETE, and SELECT with the FOR UPDATE clause.

What are the options for SHUTDOWN a DATABASE?

SHUTDOWN NORMAL

Normal database shutdown proceeds with the following conditions:

• No new connections are allowed after the statement is issued.
• Before the database is shut down, Oracle waits for all currently connected users to disconnect from the database.
• The next startup of the database will not require any instance recovery procedures.

SHUTDOWN IMMEDIATE

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 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.

SHUTDOWN TRANSACTIONAL

When you wish to perform a planned shutdown of an instance while allowing active transactions to complete first, use the SHUTDOWN command with the TRANSACTIONAL option:

• After submitting this statement, no client can start a new transaction on this instance. If clients attempt to start a new transaction, they are disconnected. After all transactions have completed, any client still connected to the instance is disconnected. At this point, the instance shuts down just as it would when a SHUTDOWN IMMEDIATE statement is submitted.
• A transactional shutdown prevents clients from losing work, and at the same time, does not require all users to log off. 

SHUTDOWN ABORT

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 work.
• 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.