Sherrie,
First, the Oracle documentation does a pretty good job of explaining
how undo works. check out the concepts manual.
Second, you might want to read Dan Fink's papers on Undo Internals, you
can find them on his website at
http://www.optimaldba.com/library.html
He does a very good job of explaining how undo works.
Lastly, I would verify that the vendor's DBA has actually worked with
Oracle before. Oracle DOES NOT make a copy of the entire physical table
for every table involved in every query, nor does it hold onto those
copies for the length of the retention period.
Retention period is misleading, as Oracle WILL overwrite information in
an undo segment, even if the retention time has not been reached, if
space is needed. Dan does an excellent job of explaining that.
He's off at the Hotsos Clinic now (lucky man!) or he'd be answering
this himself
- Sherrie.Kubis_at_swfwmd.state.fl.us wrote:
> I have a 2gb UNDO tablespace. A third-party application continually
> runs
> out of UNDO when it joins two tables to produce a result table. Our
> retention time is set to 15 minutes, the NoSpaceErrCnt in V$UNDOSTAT
> is
> always zero. The answer for this from our vendor is to increase the
> size
> of the UNDO based on their DBAs statement that UNDO is consumed
> rapidly
> because every query makes a physical copy of all tables and holds on
> to
> them for the retention period. I can find nothing that discusses
> exactly
> how UNDO physically works, and am not sure that this can be true.
> That
> would mean that every user querying our database would have copies of
> the
> tables in the UNDO, and I'd need about a gazillion gb to handle that.
> Does
> anyone have any insights on how the UNDO physically works?
>
>
>
> ---------------
> Sherrie Kubis
> Southwest Florida Water Management District
> 2379 Broad Street
> Brooksville FL 34604-6899
>
> Phone: (352) 796-7211, Ext. 4033
> Fax: (352) 754-6776
> Email: Mailto:Sherrie.Kubis_at_swfwmd.state.fl.us
> http://WaterMatters.org
>
>
>
>
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>
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Received on Tue Aug 12 2003 - 09:24:23 CDT
