In Memory Undo
676285Dec 13 2009 — edited Dec 23 2010
Does IMU generate redo for ALL data changed?
I guess that in case of the IMU transaction undo segment header is modified at the begining ( for ITL entries) and so that would need redo.
But since the actual IMU is in the shared pool, no redo is generated , and when an IMU flush happens the proper undo block is updated with the "collapsed" data.
I went through two quality materials on this subject
Both seem to suggest that redo is generated, but the wordings in the second paper suggests that ALL redo for the undo "blocks" are recorded in the redo stream, whereas the first paper suggests that redo is generated only for the "collapsed" values.
I am doubting whether my confusion arises out of the "throwaway" undo and "normal" IMU operations.
Any assistance would be welcome and thanks in advance!!
Edited by: indhar on Dec 13, 2009 6:39 PM
Edited by: indhar on Dec 13, 2009 6:40 PM