Re: Question about Undo segments

In article <3CCD881D.3F6F81D0_at_mitre.org>, Peter says...
>
>As a followup on this auto vs manual redo/undo...
>
>If you are running 9i in auto redo mode, can a session specify that it
>wants to use an old fashioned manual RBS (via SET TRANSACTION) for a
>redo intensive load job?

Nope. If you try it you'll either get an error if UNDO_SUPPRESS_ERRORS is not set to TRUE or the statement will be ignored if it is set to true.

>
>tx
>Peter
>
>"Howard J. Rogers" wrote:
>>
>> "Md Irfan" <irfan_pk_at_hotmail.com> wrote in message
>> news:c42168e7.0204280827.47e90793_at_posting.google.com...
>> > "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?
>> >
>>
>> No. "Undo segment" is just the name we give to rollback segments when 9i
>> uses the automatic method of managing them. If you use the manual method of
>> managing them, they are still called rollback segments. Obviously you can't
>> simultaneously be using both the automatic and the manual method of managing
>> them, so it is impossible to have both undo segments and rollback segments
>> being used simultaneously. It's one or the other.
>>
>> Set undo_management=MANUAL, you have rollback segments. Set
>> undo_management=auto, you have undo segments. Which ever one you are NOT set
>> to, if it exists at all, remains dormant and unused. If you've created
>> rollback segments, and switch to AUTO, those rollback segments are not
>> written to at all. If you have an undo tablespace and you switch to MANUAL,
>> the undo tablespace is not used at all -it's just dead disk space.
>>
>> Regards
>> HJR
>>
>> > >
>> > > 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

HTH. Additions and corrections welcome.

Pete

SELECT standard_disclaimer, witty_remark FROM company_requirements; Received on Mon Apr 29 2002 - 13:35:09 CDT