| Oracle Architecture [message #536816] |
Fri, 23 December 2011 03:38  |
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kamran0931
Messages: 17
Registered: December 2011
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Junior Member |
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Hi
i was studying Oracle architecture i learnt evrything but i am a bit confused.
For example if i want to update a row then through what procedure will it go?
First of all user will connect to the server using user process through server process, after establishing connection PGA will be allocated
then server process will check the sql statement in shared pool of SGA, if it's there then ok but if not then it will parse it and will keep it
in shared pool. Then server process will check the acquire data in the database buffer cache if its there then it will update it otherwise it will retrieve the data from the data files.
So if a the old value of a row is 100 and i want to update it to 200. Then;
1)Database buffer cache will have 200 value? correct?
2)The before image copy will be written into the undo segment? correct? which is 100.
3)what will be stored in redo log buffer? Regarding my example of updating from 100 to 200 please explain
I am new to oracle so if i am wrong then correct me.
Thanks
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| Re: Oracle Architecture [message #536833 is a reply to message #536832] |
Fri, 23 December 2011 04:48  |
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ramoradba
Messages: 2457
Registered: January 2009
Location: AndhraPradesh,Hyderabad,I...
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Senior Member |
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Quote:Redo Log Contents
Redo log files are filled with redo records. A redo record, also called a redo entry, is made up of a group of change vectors, each of which is a description of a change made to a single block in the database. For example, if you change a salary value in an employee table, you generate a redo record containing change vectors that describe changes to the data segment block for the table, the undo segment data block, and the transaction table of the undo segments.
Redo entries record data that you can use to reconstruct all changes made to the database, including the undo segments. Therefore, the redo log also protects rollback data. When you recover the database using redo data, the database reads the change vectors in the redo records and applies the changes to the relevant blocks.
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| Re: Oracle Architecture [message #536844 is a reply to message #536838] |
Fri, 23 December 2011 05:22 |
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kamran0931
Messages: 17
Registered: December 2011
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Junior Member |
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Thanks ramoradba i got it.
It stores changes made to the data segment block for the table, the undo segment data block and the transaction table of the undo segments.
And it is a binary operation, bits and bytes; enough to replay the change.
Thanks
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