| online redo logs [message #155820] |
Wed, 18 January 2006 16:21  |
siznad
Messages: 2
Registered: January 2006
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Junior Member |
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I'm new to Oracle, so forgive me if this is a stupid question.
I'm learning about backup, recovery, etc. I'm trying to understand the concept of redo log files. I understand they can be used with a database backup to recover a damaged database. I have read that there are online redo logs and archived redo logs. Archived redo logs I understand because I can see them on the disk. Online redo logs I do not get.
Are the online redo logs something stored in memory? If so, how can a database be recovered if a system crashes and everything in memory is lost.
I would appreciate any clarification.
Thanks.
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| Re: online redo logs [message #155899 is a reply to message #155820] |
Thu, 19 January 2006 09:59  |
sunil_v_mishra
Messages: 506
Registered: March 2005
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Senior Member |
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hi,
redo log are logs store in redo log files...
this log are there to recover the database when data base is crashed
Database is crashed when any of its datafile is missing or corrupted or control file or redo file get corrupted.....
If will be better for you to read Oracle Database architecture once you will be tharo with that you will understand what exactly redo log files and redo logs are....
Yea redolog are stored in redo log file.
when i say file that means it is physical file store in memory i.e.hardisk.
Regards
Friendly sunilkumar
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| Re: online redo logs [message #156149 is a reply to message #155820] |
Mon, 23 January 2006 02:07 |
chj733
Messages: 11
Registered: October 2005
Location: CHINA
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Junior Member |
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HI
online redo logs are real physical files,they stay somewhere on your OS,just like WORDS,EXCEL,MPS,ets.You can use the following SQL to have a look
SELECT * FROM V$LOGFILE
ORACLE use lgwr process write log buffer to online redo logs ,when the current logfile group is full,it will switch to the next group.If your database is running in archiving mode,before Oracle clearing the next logfile group,he must "copy" the contents of the group to archive dest,then he clear the group,and write redo records to the group,and then the group became the current group after switching,a checkpoint will be latched during the switch
[Updated on: Mon, 23 January 2006 02:09] Report message to a moderator |
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