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Home -> Community -> Mailing Lists -> Oracle-L -> RE: UNDO Tablespace
>"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.
Sherrie,
In my considered opinion: Woohoohoohoo.
That's a ridiculous thing for a DBA to say. I hope he was misinterpreted
somewhere down the line because otherwise he's got a very flimsy grasp of
the read-consistency model.
In very simple terms Undo is used to hold a copy of any changed data (not
the whole table!) which has not been committed and flushed to the datafiles.
While it's there the data for an update transaction is available a) to the
'owning' transaction in case it has to ROLLBACK the updates it's made. b)
to any other transactions which need to reconstruct the data as it was
before the update began.
On a more positive note I agree that we need the text of the error message in order to give some help.
Cheers,
Mike
> 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
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