Home » RDBMS Server » Server Administration » instance recovery....
instance recovery.... [message #259591] Thu, 16 August 2007 01:13 Go to next message
amansharma81
Messages: 8
Registered: June 2005
Location: India
Junior Member

Hi there,
Probably thats a very much basic question but some how I am much confused somehow in it.
I have read the concept and backup/recovery guide.
My doubts are as follows
(1) How Oracle starts finding the blocks to be recovered at the mount stage?Will it go and scan the entire datafiles of the db to find the blocks which are not consistent?f not than out of the whole datafiles,how it will distuinguish those who needs recovery and are going to get committed data?This doubt is for the roll forward at the mount stage.
(2)In the open stage, there may be a stage when the old data in the undo is already purged/overwritten of one transaction by another.If that will happen than how ORacle will get the old data for that transaction?
thanks in advance and regards,
Aman....
Re: instance recovery.... [message #259601 is a reply to message #259591] Thu, 16 August 2007 01:46 Go to previous messageGo to next message
Michel Cadot
Messages: 64152
Registered: March 2007
Location: Nanterre, France, http://...
Senior Member
Account Moderator
1) Oracle applies active online redo logs on each file. It knows for each file what was the last checkpoint time (scn) as this is in the header of the file

2) Old data are in the rollback/undo segments that were recovered in the first phase.

Regards
Michel
Re: instance recovery.... [message #259670 is a reply to message #259601] Thu, 16 August 2007 04:18 Go to previous messageGo to next message
amansharma81
Messages: 8
Registered: June 2005
Location: India
Junior Member

Hi Michel,
(2)Thanks.I got it.
(1)I am not still clear.Can you please elobarate a bit more?
Thanks and regards,
Aman....
Re: instance recovery.... [message #259677 is a reply to message #259670] Thu, 16 August 2007 04:29 Go to previous messageGo to next message
Michel Cadot
Messages: 64152
Registered: March 2007
Location: Nanterre, France, http://...
Senior Member
Account Moderator
During the first pass, rollforward, Oracle also rolls forward the undo segments.
So in the second pass, rollback, Oracle can find in the undo segments the old data it has to restore.

Regards
Michel
Re: instance recovery.... [message #259893 is a reply to message #259677] Thu, 16 August 2007 14:43 Go to previous messageGo to next message
amansharma81
Messages: 8
Registered: June 2005
Location: India
Junior Member

Hi Michel,
For
(1) How Oracle starts finding the blocks to be recovered at the mount stage?Will it go and scan the entire datafiles of the db to find the blocks which are not consistent?f not than out of the whole datafiles,how it will distuinguish those who needs recovery and are going to get committed data?This doubt is for the roll forward at the mount stage.
You replied
Oracle applies active online redo logs on each file. It knows for each file what was the last checkpoint time (scn) as this is in the header of the file.
My doubt is that will oracle apply the all of online redolog file
s or it will start from only those redo enteries which are ahead form the current Redo Byte Address?
Thanks and best regards,
Aman....
Re: instance recovery.... [message #259895 is a reply to message #259893] Thu, 16 August 2007 14:50 Go to previous messageGo to next message
Michel Cadot
Messages: 64152
Registered: March 2007
Location: Nanterre, France, http://...
Senior Member
Account Moderator
ahead from the last (incremental) checkpoint.

Regards
Michel
Re: instance recovery.... [message #259938 is a reply to message #259895] Thu, 16 August 2007 21:24 Go to previous message
amansharma81
Messages: 8
Registered: June 2005
Location: India
Junior Member

Thanks Michel.
Regards,
Aman....
Previous Topic: How to modify the existing un-partitioned indexes to partitioned indexes on partitioned tables?
Next Topic: ORA-01031: insufficient privileges when trying to connect as sysdba
Goto Forum:
  


Current Time: Sat Dec 10 06:49:07 CST 2016

Total time taken to generate the page: 0.06185 seconds