| Database Buffer to Redo Log Buffer? [message #62675] |
Mon, 09 August 2004 02:03  |
Pratap Zope
Messages: 23
Registered: July 2004
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Junior Member |
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Hi,
when updates are made in database,
the Data blocks required are serached in data buffer cache, if not found then are read from datafle and kept in database buffer cache, then they are modified in data buffer cache to make them 'dirty' or those are modified in 'log buffer' and then are copied to data buffer cache?
also redo buffer has before and after image of data?
however in instance recovery or media recovery undo segments are used to rollback the uncommitted data, then what is the use of 'before image' in redo buffer?
Please suggest and help
Thanks,
Sincerely,
Pratap
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| Re: Database Buffer to Redo Log Buffer? [message #62680 is a reply to message #62675] |
Mon, 09 August 2004 04:32  |
Gorjan Todorovski
Messages: 9
Registered: August 2004
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Junior Member |
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Blocks are changed in the buffer cache and marked as dirty and the
redo log buffer is appended with the info, with which later it would be
possible to redo the operation. LGWR doesn't write on disk on every
DML operation.
Undo info is not stored in the redo logs but it can be generated from
the info contained in it (like the LogMiner utility).
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www.oracleclinic.com
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