In a typical use case, you manually shut down the database, making it unavailable for users while you perform maintenance or other administrative tasks. You can use the SQL*Plus SHUTDOWN command or Enterprise Manager to perform these steps.
Phase
Mount Stage
Description
1
Database closed
The database is mounted, but online data files and redo log files are closed.
2
Database unmounted
The instance is started, but is no longer associated with the control file of the database.
3
Database instance shutdown
The database instance is no longer started
Shutdown Modes
A database administrator with SYSDBA or SYSOPER privileges can shut down the database using the SQL*Plus SHUTDOWN command or Enterprise Manager. The SHUTDOWN command has options that determine shutdown behavior.
Database Behavior
Abort
Immediate
Transactional
Normal
Permits new user connections
No
No
No
No
Waits until current sessions end
No
No
No
Yes
Waits until current transactions end
No
No
Yes
Yes
Performs a checkpoint and closes open files
No
Yes
Yes
Yes
• 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.
Because SHUTDOWN ABORT does not checkpoint the open data files, instance recovery is necessary before the database can reopen. The other shutdown modes do not require instance recovery before the database can reopen.
• 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.
• 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.
• SHUTDOWN NORMAL
This is the default mode of shutdown. The database waits for all connected users to disconnect before shutting down.
How an Instance Is Shut Down?
The final step in database shutdown is shutting down the instance. When the database instance shuts down, the SGA ceases to occupy memory, and the background processes terminate.
In unusual circumstances, shutdown of a database instance may not occur cleanly. Memory structures may not be removed from memory or one of the background processes may not be terminated. When remnants of a previous instance exist, a subsequent instance startup may fail. In such situations, you can force the new instance to start by removing the remnants of the previous instance and then starting a new instance, or by issuing a SHUTDOWN ABORT statement.
In some cases, process cleanup itself can encounter errors, which can result in the termination of process monitor (PMON) or the instance. The dynamic initialization parameter INSTANCE_ABORT_DELAY_TIME specifies how many seconds to delay an internally generated instance failure. This delay gives you a chance to respond. The database writes a message to the alert log when the delayed termination is initiated.
In some circumstances, by allowing certain database resources to be quarantined, the instance can avoid termination.
