| Re: Regarding internal Mechanism of oracle [message #369492] |
Tue, 03 October 2000 04:58 |
Krishna Gopalan
Messages: 1
Registered: October 2000
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Junior Member |
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U said it
I'm trying to find an answer to my questions about how Oracle actually does its updates and inserts. Here is the thread Hope u can understand and make it clear I want clear answers and not the stuff the books try to answer and confuse u!
1. During a Select the Data blocks are pulled into the Db Buffer cahce (if not already there) and the records are displayed/processed.
I think i am right on that.
2. During a an update What happens. I understand that the data block to be updated is pulled into the db buffer (right?)At WHAT point of time is the data block really modified with the new data?
Is is after the commit? ( in which case the data block should be always in the buffer even after a disk write since otherwise a commit operation cannot write to the data block) If before a commit then what happens if the commit is delayed and meanwhile the checkpoint or (3 secs ) occurs and all the modified (dirty) blocks are writtedn to disk. Will the rollback again bring in the changed datablock and remodify it? What blocks will another sql from another session read since read consistency has to be maintained?
In case of an insert statement, are all the databalocks required to hold the new rows called to the database buffer cache? when will the blocks be actually filled with new rows before or after commit?
Tho I scored 59/63 in my Oracle8 DBA exam this point stupifies me. Please answer
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