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Maintaining Online Redo LogFiles

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Objectives

•After completing this lesson, you should be able to do the

following

•!"plain the purpose of online redo log files

•Outline the structure of online redo log files•#ontrol log switches and chec$points

•Multiple" and maintain online redo log files

•Manage online redo logs files with OMF

•Obtain online redo log file information

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%sing Online Redo Log Files

Online Redo log files have the following

characteristics

•Record all changes made to data

•&rovide a recovery mechanism

•#an be organi'ed into groups

•At least two groups re(uired

Redologfiles

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)ow Online Redo Log Files

*or$ •Online Redo log files are used in a cyclic fashion+•*hen a online redo log file is full, L*R will move to the ne"t log

group+

•#alled a log switch

•#hec$point operation also occurs

•-nformation written to the control file

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Forcing Log .witches and

#hec$points

•Forcing a log switch

•#hec$points can be forced by

•.etting FAST_START_MTTR_TARGET parameter 

•ALTER SYSTEM CHECKPOINT command

 ALTER SYSTEM CHECKPOINT;

 ALTER SYSTEM SWITCH LOGFILE;

FAST_START_MTTR_TARGET = 600

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Adding Online Redo Log File

roups

Group

1

Group

2

Group

3

 ALTER DATABASE ADD LOGFILE GROUP 3('$HOMEORADATA!0"#%3&)'* '$HOMEORADATA!0+#%3,)'-SI.E "M;

#%3,)

#%3&)#%"&)

#%",)

#%+&)

#%+,)

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Adding Online Redo Log File

Members ALTER DATABASE ADD LOGFILE MEMBER '$HOMEORADATA!0/#%")' TO GROUP "*'$HOMEORADATA!0/#%+)' TO GROUP +*'$HOMEORADATA!0/#%3)' TO GROUP 3;

Group

1

Group

2

Group

3

#%"&)

#%",)

#%+&)

#%+,)

#%") #%+)

#%3&)

#%3,)

#%3)

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/ropping Online Redo

Log File roups

 ALTER DATABASE DROP LOGFILE GROUP 3;

#%"&) #%+&) #%3&)

Group

1

Group

2

Group

3

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/ropping Online Redo

Log File Members

 ALTER DATABASE DROP LOGFILE MEMBER'$HOMEORADATA!0/#%3)';

Group

1

Group

2

#%",)

#%")

#%"&)

#%",)

#%+)

#%"&)

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Relocating or Renaming

Online Redo Log Files•Relocate or rename online redo log files in one of the twofollowing ways

•ALTER DATABASE RENAME FILE command

•.hut down the database+•#opy the online redo log files to the new location+

•&lace the database in MOUNT mode+

•!"ecute the command+

•Open database for normal operation+

•Add new members and drop old members+

 ALTER DATABASE RENAME FILE'$HOMEORADATA!0"#%+&)'TO '$HOMEORADATA!0+#%")';

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#learing Online Redo Log

Files•ALTER DATABASE CLEAR LOGFILE commandcan be used to reinitiali'e an online redo log file+

•%se the UNARCHIVED $eyword to avoid archiving the

corrupted online redo log file+ ALTER DATABASE CLEAR UNARCHI1ED

LOGFILE GROUP +;

 ALTER DATABASE CLEAR LOGFILE GROUP +;

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Managing Online Redo Log

Files with OMF•/efine the DB_CREATE_ONLINE_LOG_DEST_n 

 parameter

•A group can be added with no file specification

•/ropping a group

DB_CREATE_ONLINE_LOG_DEST_"

DB_CREATE_ONLINE_LOG_DEST_+

 ALTER DATABASE DROP LOGFILE GROUP 3;

 ALTER DATABASE ADD LOGFILE;

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Obtaining roup and Member

-nformation•-nformation about a group and its members can be obtained by(uerying the following views

•V$LOG

•V$LOGFILE

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Archived Redo Log Files

•Accomplished automatically by AR#n

•Accomplished manually through .2L statements

•*hen successfully archived

•An entry in the control file is made•Records archive log name, log se(uence number, and high and low

system change number 3.#45

•Filled online redo log files cannot be reused until

•A chec$point has ta$en place

•File has been archived by ARCn 

•#an be multiple"ed

•Maintained by the /1A

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.ummary

•-n this lesson, you should have learned how to

•!"plain the use of online redo log files

•Obtain online redo log file information

•#ontrol log switches and chec$points•Multiple" and maintain online redo log files

•Manage online redo log files with OMF

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&ractice 6 Overview

•0his practice covers the following topics

•#reating online redo log file groups and members

•Maintaining online redo log file groups and members

•Managing online redo log files using OMF