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SCN [message #322263] Thu, 22 May 2008 23:29 Go to next message
hexmanju
Messages: 71
Registered: September 2005
Location: MUMBAI
Member
Hi

I read about CTWR Process in Oracle Database 10g.It says the process records the list of blocks in each data file that have changed.
This way whenever an RMAN incremental backup occurs it just makes use of this file to identify the new blocks and does not need to scan
the entire Datafile to find blocks that have changed.

This has led me to a question as

1)How does it know the block A has changed.Does it know my comparing Block SCN currently versus SCN stored in last backup

My second question is

2)When a transaction commits and say if SCN gets updated in redo log, at checkpoint time, does CKPT updates the header of all datafiles
with this latest SCN.So just a confusion arised for me that

Even though the transaction occured for block A in tablespace A and incremented the SCN ,this increment updated all the datafile headers
even though no block changes were done in other datafiles?

3)Third Question is IS there anything called Block level SCN ,or is it that Block Level SCN is the same number as that stored in its datafile header


I know the fact that all datafile headers have to be the same SCN to open the Database.

Kindly explain?

Thanks
MM

Re: SCN [message #322290 is a reply to message #322263] Fri, 23 May 2008 00:31 Go to previous message
Michel Cadot
Messages: 64137
Registered: March 2007
Location: Nanterre, France, http://...
Senior Member
Account Moderator
1) Yes
2) CKPT updates the header of each datafile with checkpoint SCN, no relation with commit
3) You can called block scn, the scn of the last block modification. No relation with datafile checkpoint scn.

Regards
Michel
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