|
"The mistakes
are all waiting to be made." - chessmaster Savielly
Grigorievitch Tartakower (1887-1956) - on the game's opening
position |
Read
first then play the video:
DBA009(VIDEO)-Multiplexing
and Maintaining the Online Redo Log files
You must first Register
and then request for username and password
to access to VIDEOS
Multiplexing and
Maintaining the Online Redo Log files
Introduction
As a DBA, you are
responsible for maintaining multiple Online Redo log files to protect
your organization of a possible loss of data due to media failure.
Your job’s responsibilities dictate that you should at least be
informed of the following basic fundamental subjects:
Maintaining the Online Redo
Log files
Multiplexing the Online
Redo Log files
Using Oracle-Managed Files
Using User-Managed Files
Using the
DB_CREATE_ONLINE_LOG_DEST parameter
Creating an Online Redo Log
group
Creating an Online Redo Log
member
Clearing an Online Redo Log
group
Dropping an Online Redo Log
group
Using the V$LOGFILE view
Commands:
SHOW PARAMETER
HOST MKDIR
ALTER SYSTEM SET
ALTER DATABASE ADD LOGFILE
GROUP
ALTER DATABASE ADD LOGFILE
MEMBER
ALTER DATABASE CLEAR
LOGFILE GROUP
Hands-on
In this exercise you will learn how to maintain and multiplex the
online redo log files using Oracle-Managed Files (OMF).
Connect to a database
First, connect to SQL*Plus as the system/manager user.
SQL> CONNECT system/manager@school AS
SYSDBA
Oracle-Managed Files
Check to see that the database is using Oracle-Managed Files.
SQL> SHOW PARAMETER
db_create_online_log_dest
If the value of all of the DB_CREATE_ONLINE_LOG_DEST column
were null, it means that you cannot take advantage of Oracle-Managed
Files.
Create a directory
Create a directory called
c:.
SQL> HOST MKDIR c:
Now, the folder was created.
Define Oracle Managed folder
Alter the system so that
the database will manage the Online Redo Log files in the Online Redo
Log destination 4.
SQL> ALTER SYSTEM SET
db_create_online_log_dest_4='c:'
/
Display the DB_CREATE_ONLINE_LOG_DEST parameter again.
SQL> SHOW PARAMETER
db_create_online_log_dest
Notice that there is a value for the log destination 4.
Add a group file using
Oracle-Managed file
Alter the database to add one more group to the online redo log
files.
SQL> ALTER DATABASE ADD LOGFILE GROUP 4
/
Query the V$LOGFILE view.
SQL> SELECT * FROM v$logfile
/
Notice the Oracle naming convention. The 4 indicates the
group number.
Add a log file member
Add a member to the Online Redo Log files group number 4, using
Oracle-Managed Files (OMF).
SQL> ALTER DATABASE
ADD LOGFILE MEMBER
'redo04b.log' TO GROUP 4
/
Query the V$LOGFILE view.
SQL> SELECT * FROM v$logfile
/
Notice the new member status is set to invalid. That's
okay. Once we start using it, the status will change.
Clear a log file group
Clear Online Redo Log file group number 1.
SQL> ALTER DATABASE CLEAR LOGFILE GROUP 1
/
You should never execute this command unless you have to.
By executing this command you may loose some important information. Do
this command only if your group file has a corrupted member.
Drop a log file group
Drop the group number 4 of
the Online Redo Log file.
SQL> ALTER DATABASE DROP LOGFILE GROUP 4
/
Notice that when you use Oracle-Managed Files, you do not
need to delete the physical datafile from the system using the
Operating System command. Oracle does it for you.
|
"Reality is
merely an illusion, albeit a very persistent one." - Albert
Einstein (1879-1955) |
Questions:
Q: Why do you multiplex an
online redo log file?
Q: How do you multiplex an
online redo log file?
Q: Describe the
Oracle-Managed files.
Q: Describe the
User-Managed files.
Q: What are the differences
between an Oracle-Managed and User-Managed files?
Q: How do you create an
online redo log member?
Q: What does the following
SQL statement?
SQL> ALTER SYSTEM SET
db_create_online_log_dest_4='c:'
/
|
