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hot backup [message #151502] Thu, 15 December 2005 03:29 Go to next message
risy_s
Messages: 44
Registered: September 2005
Location: Mumbai
Member
hello everybody

plz clear my doubts


when i put my tablespace in hot backup mode the header of the datafile is freez means scn will not move ahead though the datafiles is updating oracle will write whole block image to the redolog files instead of writing only change vector.....


now suppose i have put usr(1datafile) tablespace in hot backup
so datafile header in this datafile is frozen at 123 scn... writing to this datafile is running bcoz db is online.... other datafile except this tablespace are also updating and and scn in this datafile is also 123 when i started hotbackup of usr datafile now other datafile are updating and its scn reaches to 130 now i m ending the hotbackup of usr tablespce it still contains scn 123... so afte ending hotbackup all datafile must be consistent

so how this scn 123 is updated to scn no 130 to make consistency to other datafiles....

risy....

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Re: hot backup [message #151668 is a reply to message #151502] Fri, 16 December 2005 01:50 Go to previous message
sadashiv_tv
Messages: 3
Registered: November 2005
Location: Bangalore
Junior Member
Risy,

When the hot backup going, we know the database can be making changes to the data files. So as the datafile header frozen, but the changes are being made, thus making the backup inconsistent.

when you put back the tablespace end backup, the database uses information logged in the redo logs to build a consistent image of the data. This is the reason,that the DB must be in Archive Log mode before you can put a tablespace in backup mode. It is the combination of freezing the data file header's SCN and the redo logs that create a consistent data file from the inconsistent backup image( redo log vector). Now the database starts at the SCN in the frozen header and applies any changes to that data file since that SCN was frozen. So now it becomes consistent.

I belive you got the ans.

Shiv

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