RE: Estimating space needed for UNDO tablespaces

Thanks for the reply Dan.

Would you suggest setting UNDO_RETENTION to roughly the length of time of the longest
running job in the database? For example, in our DW, our BI analysts tell me that their
longest batch run is about 1 hr 45 minutes. My uneducated guess is to accordingly
set the parameter to approx 2 hours.

-----Original Message-----
Sent: Friday, September 26, 2003 4:15 PM To: Multiple recipients of list ORACLE-L

That is a good place to start. You might consider adding a little if you have many concurrent transactions or want to increase the undo_retention to a high number. Once you are using AUM, keep a close eye on v$undostat, though there are some known issues with it not populating properly, keep an eye on the begin_time and end_time. However, for estimation purposes it should work.

Daniel Fink

Thomas Jeff wrote:

> I'm beginning the process of converting over to automatic
> undo management. I'm wondering as to exactly how large to
> initially build the UNDO tablespace. Make it roughly
> the same size as the sum of the current rollback
> tablespaces? Or has your experience been different,
> i.e., you've found you've generally needed more or less
> space with respect to the previous allocation for rollback
> segments (manual undo)?
>
> Thanks.
>
> --------------------------------------------
> Jeffery D Thomas
> DBA
> Thomson Information Services
> Thomson, Inc.
>
> Email: jeff.thomas_at_thomson.net
>
> Indy DBA Master Documentation available at:
> http://gkmqp.tce.com/tis_dba
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