Overview Database Instance Shutdown

Question 1

Steps in Consistent Shutdown

Answer 1

1) Database Closes - The db is mounted but online data and redo log files are closed.
2) Database Unmounts - The instance is started but is no longer associated with the control file of the db
3) Database instance shuts down - The db instance is no longer started

Question 2

Shutdown Modes

Answer 2

The db administrators SYSDBA and SYSOPER can shut down the db using SQLPlus or Enterprise Manager.

1) SHUTDOWN ABORT
2) SHUTDOWN IMMEDIATE
3) SHUTDOWN TRANSACTIONAL
4) SHUTDOWN NORMAL

Question 3

SHUTDOWN ABORT

Answer 3

+ Intended for Emergencies when no other form of shutdown is successful.
+ A subsequent open of this db may take substancially 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
+ Other shutdown modes do not require instance recovery before the database can reopen

Question 4

SHUTDOWN IMMEDIATE

Answer 4

+ Typically the fastest next to ABORT.
+ Terminates any executing SQL statements and disconnects users.
+ Active transactions are terminted and uncommitted changes are rolled back.

Question 5

SHUTDOWN TRANSACTIONAL

Answer 5

+ Prevents users from starting new transactions .
+ Waits for all current transactions to complete before shutting down.
+ This mode can take significant amount of time depending on the nature of the current transactions.

Question 6

SHUTDOWN NORMAL

Answer 6

+ Default mode of shutdown

+ The database waits for all connected users to disconnect before shutting down.

Question 7

How a Database Is Closed

Answer 7

The nature of the database close operation depends on whether the database shutdown is normal or abnormal.
+ Closed during normal shutdown -
++ Oracle Database writes data in the SGA to the data files and online redo log files
++ Afterwards, the db closes online data and redo log files.

+ Closed during Abnormal Shutdown
++ If abnormal termination occurs (SHUTDOWN ABORT), then the instance of an open db closes and shutsdown the db instantanieously.
++ Oracle db does not write data in the buffers to the data and redo log files.
+ The subsequent reopening of the db requires instance recovery, which Oracle performs automatically.

Question 8

How a Database Is Unmounted

Answer 8

After the bd is closed, Oracle db unmounts the db to disassociate it from the instance.
+ After the db is unmounted, Oracle db closes the control files of the db.

Question 9

How an Instance Is Shut Down

Answer 9

+ When the db instance shutsdown, the SGA ceases to occupy memory, and the background processes termintate.
+ In unusual circumstances, shutdown of a db instance may not occur cleanly. Memory structures may not be removed from mem or one of the background processes many not be terminted.
+ When remnants of a previous instance exists, a subsequent instance startup may fail.
+ In such situations, you can force the new instance to start by removing remnats of the previous instance and then starting the new instance or issuing a SHUTDOWN ABORT.
+ In some cases, process cleanup itself can encounter errors, which can result in the termination of PMON or the instance.
+ The dynamic initialization parameter INSTANCE_ABORT_DELAY_TIME specifies how many seconds to delay an internally generated instance failure. The db writes messages to the alert log when delayed termination is initiated. In some cases allowing certain db resources to the quarantined