| Problem regarding oracle architecture [message #59537] |
Tue, 02 December 2003 04:13  |
ora
Messages: 47
Registered: June 2002
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Member |
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Hi,
I have two doubts regarding Oracle Architecture
1) At chechpoint all the dirty list get written to the disk or only the committed records in dirty list get written ?
if the answer is all the dirty list then how can we say that after checkpoint DB is in consistent state.
And if only committed records get written then when a long transaction takes all the buffers in buffer list and not a sigle buffer contain any committed data and all the buffers get full but the transaction is still executing. will oracle flush the uncommitted data to disk or not?
2) What get stored in redo log file means only command or data too?
Plz pull me out from these problems
Thanx in advance
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| Re: Problem regarding oracle architecture [message #59541 is a reply to message #59537] |
Tue, 02 December 2003 08:41  |
Thiru
Messages: 1089
Registered: May 2002
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Senior Member |
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At checkpoint , the DBWR process writes ALL dirty buffers(ie buffers that have been modified ) whether they are committed or not. The database is consistent with respect to that Checkpoint SCN, irrespective of the uncommited data (that may be comitted later or rolled back) becos the necessary undo in the rollback segments that identifies the state of the transaction as well as undo entries to rollback the changes during instance recovery are safely written already + the REDO of the table/undo segments have already been written to the online redolog files by the LGWR. The datafile headers and controlfiles are updated with that checkpoint SCN .
Also pls see my earlier posts , that might help you..
1)
http://www.orafaq.net/msgboard/server/messages/21651.htm
2)
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