undo retention vs performance

Can somebody please give me a clear answer and explanation to this?

Some people say it would affect my performance, others say that it wouldn't...    

I quote: "If you have too high of undo retention parameter, you need to have the corresponding big enough space to hold all the info. If not the performance will be hampered."  

But i don't know what to believe, the people that say it wouldn't have influence on my performance say this is beacause the space will be just overwritten. But doesn't it take time to re-allocate the space then or something??  

Here is some extra information:  

Db Version 9.2.0.5.0  

UNDO INFO:

undo_management : AUTO

undo_tablespace : UNDO01

undo_suppress_errors : FALSE

undo_retention : 96000  

UNDO SIZE (MB) UNDO RETENTION (SEC) OPTIMAL UNDO RET.(SEC) NEEDED UNDO SIZE (MB)

• -------------------- ----------------------

  ---

         65535                96000                  26748

This information is gathered by some queries i ran... (also the optimal retention/size)

You see the undo size is way too small for the undo_retention parameter
(maxsize of undo tablespace is already reached).
 

(Ps this database really has some performance issues.)
   

Thanks for your help!

Best regards,

Mathieu  

-----Oorspronkelijk bericht-----

Van: Gu Eileen [mailto:Eileen.Gu_at_tic.toshiba.com]

Verzonden: maandag 22 maart 2010 17:42

Aan: Braekeveld, Mathieu

Onderwerp: RE: undo retention parameter  

If you have too high of undo retention parameter, you need to have the corresponding big enough space to hold all the info. If not the performance will be hampered.        

-----Original Message-----

Subject: undo retention parameter  

Hi,    

Question: Can a too high value in the undo retention parameter cause performance problems?  

And if so, why is that?    

Thanks for your help!  

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