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"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:
DBA-VIDEO -Multiplexing
and Maintaining the Online Redo Log files
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.
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"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:'
/
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