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Regarding Oracle Achitecture [message #244319] Tue, 12 June 2007 05:46 Go to next message
Lavjeet
Messages: 5
Registered: June 2007
Junior Member
This is regarding Oracle Achitecture :
In this case two users are logged in Database.User1 updates a row in the Emp table and commits the record. This will save the changes in Redo Log files.Now User2 views the updated record from Emp table,updates it and commits.This will again save the changes in Redo Log files.Now when a checkpoint occurs how will DBWR know which updated copy to save in Data File . How does SCN helps in this case ? Can a dirty buffer block be updated twice ?
Can you let me know from where should I read this in detail ?
Re: Regarding Oracle Achitecture [message #244339 is a reply to message #244319] Tue, 12 June 2007 07:00 Go to previous messageGo to next message
Michel Cadot
Messages: 64103
Registered: March 2007
Location: Nanterre, France, http://...
Senior Member
Account Moderator
Changes are made directly in the block only change vectors (the way how to change) are recorded in redo logs.
So successive changes modify the same block and the checkpoint only see the cumulative changes.

Regards
Michel
Re: Regarding Oracle Achitecture [message #244341 is a reply to message #244339] Tue, 12 June 2007 07:10 Go to previous messageGo to next message
Lavjeet
Messages: 5
Registered: June 2007
Junior Member
I am not still having a clear idea Michel.Please elaborate on what do you mean by : "Changes are made directly in the block only change vectors (the way how to change) are recorded in redo logs."
Also I read in a book that Oracle doesnot modify the same block in database buffer which is marked dirty till it has been copied to data file.

Maybe I am not upto the level .So kindly suggest me a link from where I can read about this in detail.
Re: Regarding Oracle Achitecture [message #244348 is a reply to message #244341] Tue, 12 June 2007 07:36 Go to previous message
Michel Cadot
Messages: 64103
Registered: March 2007
Location: Nanterre, France, http://...
Senior Member
Account Moderator
Quote:
I read in a book

Which book always post your reference.

Database Concepts, Chapter 13 Data Concurrency and Consistency
This is what you have to know. The rest is Oracle internal stuff.

Regards
Michel
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