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regarding oracle architecture [message #297167] Wed, 30 January 2008 07:45 Go to next message
prajjwal
Messages: 28
Registered: January 2008
Location: kolkata
Junior Member

I have a big doubt regarding oracle architecture..

Is there a possibility that DBWR writes to datafiles directly from data buffer cache without involving the redo log files??


Please clarify data is moved from where to where :-
1) at commit
2) at log switch


...I know its a very silly question but I didnt get a good enough answer form any DBA fundamentals book.
Re: regarding oracle architecture [message #297174 is a reply to message #297167] Wed, 30 January 2008 08:01 Go to previous messageGo to next message
Frank Naude
Messages: 4502
Registered: April 1998
Senior Member
COMMIT will flush changed data to the redo logs before the commit will return.

A log switch will force a checkpoint - which will flush data from the data cache to the data files.

Oracle may sometimes write uncommitted data to data files. However, you shouldn't worry about it as it will be undone if the transaction is rolled back.

Bottom line, Oracle will guarantee that the data remains CONSISTENT.
Re: regarding oracle architecture [message #297175 is a reply to message #297167] Wed, 30 January 2008 08:02 Go to previous message
Michel Cadot
Messages: 64140
Registered: March 2007
Location: Nanterre, France, http://...
Senior Member
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Quote:
Is there a possibility that DBWR writes to datafiles directly from data buffer cache without involving the redo log files??

It happens all the time, DBWR does not care about logs.

Quote:
Please clarify data is moved from where to where :-
1) at commit
2) at log switch

No data/buffer are moved during these events.
They only involved LGWR (and later ARCH). Sometimes DBWR but as a side effect (to move forward checkpoint point).

Database Concepts
Chapter 1 Introduction to the Oracle Database
Chapter 9 Process Architecture

99% of your questions are answered in this book.
Regadrs
Michel

[Updated on: Wed, 30 January 2008 08:03]

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