How much undo/Redo will be generate ?

Question

Dear Experts,
(Oracle 10gR2,Windows 2003 Server)
We are going to shink some segments(Recommended by Segment Advisor) with total allocated size around 500G (say 5 segments there ). As shrink space need huge amount of undo/redo space, could you please suggest me how to estimate undo/redo and/or temporary space requirement for this operation( Locally managed, ASSM).
Thanks&Regards
Sunil Kumar
Edited by: sunil kumar on 04-Apr-2011 02:24

Answer 1

sunil kumar wrote:
We are going to shink some segments(Recommended by Segment Advisor) with total allocated size around 500G (say 5 segments there ). As shrink space need huge amount of undo/redo space, could you please suggest me how to estimate undo/redo and/or temporary space requirement for this operation( Locally managed, ASSM).
Interesting question - and Aman has pointed you to a generic note I wrote about undo/redo space.
Off the top of my head I think I'd look at it like this:
Size of used space BEFORE shrink - predicted size of used space AFTER shrink = total size of rows moved
total size of rows move / average row length = total number of rows moved.
Then apply the comments in the note for each row, remembering that a "move" of a row is a delete/insert, and don't forget to allow for the indexes on the row. An remember that since the object is very large the cost of random reads of INDEX blocks may be the most signficant performance problem.
Regards
Jonathan Lewis