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Re: Question about Undo segments

From: Thomas Kyte <tkyte_at_oracle.com>
Date: 28 Apr 2002 10:00:16 -0700
Message-ID: <aah9r002fo3@drn.newsguy.com>


In article <c42168e7.0204280827.47e90793_at_posting.google.com>, irfan_pk_at_hotmail.com says...
>
>"Howard J. Rogers" <dba_at_hjrdba.com> wrote in message
>news:<aafd03$9ki$1_at_lust.ihug.co.nz>...
>> Undo segments are just rollback segments with a new name. Therefore, what
>> was true for rollback segments remains true for undo segments.
>
>But I have seen there are both RBS and Undo Tablespaces in 9i. Which one is
>used for rollback.
>Is data written in both the tablespaces?

you are either using an UNDO tablespace

OR

you are using rollback segments.

You choose, both are not used at the same time.

>
>>
>> Therefore, it's your server process that modifies undo buffers. They get
>> flushed to disk as dirty buffers whenever DBWn takes it into its head to do
>> any osrt of disk writing. The redo for them is the same as it is for any
>> modification to any buffer: the before and after image.
>>
>> In short, there's nothing magic about them -and if you know how rollback
>> blocks are dealt with, that's how undo blocks are managed, too.
>>
>> Regards
>> HJR
>>
>>
>> "Jargular" <zclai_at_yahoo.com> wrote in message
>> news:8ae4ae9e.0204270719.22c0f769_at_posting.google.com...
>> > Hi,
>> >
>> > Does anybody know what is the process that writes to the Undo
>> > segments? under what condition the Undo buffers are flushed into Undo
>> > segments? how are the changes in Undo buffers recorded in the online
>> > Redologs? I seached Oracle9i documentation, it seems that they are not
>> > detailed in the docs. Anyone can help?
>> >
>> > really appreciated.
>> >
>> > Jargular
>> > zclai_at_yahoo.com

--
Thomas Kyte (tkyte@oracle.com)             http://asktom.oracle.com/ 
Expert one on one Oracle, programming techniques and solutions for Oracle.
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Received on Sun Apr 28 2002 - 12:00:16 CDT

Original text of this message

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