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Thread: undo_retention

  1. #1
    Join Date
    Feb 2008
    Posts
    38

    Unanswered: undo_retention

    hi

    As far as I know after a transaction eventhough the undo_retention is 2 hours, if there is no inactive segments in undo tablespace,the segment that is responsible for keeping data until two hours will be overwritten.

    Inorder to prevent snapshot too old errors,it is suggested to increase undo_retention.But I dont understand the reason?

    What is the negative effect if I make undo retention=0 except the usage of flashback feature.

  2. #2
    Join Date
    May 2006
    Posts
    132
    Assuming UNDO_MANAGEMENT=AUTO, the parameter UNDO_RETENTION is automatically tuned with 10g+. Unless you need a particular value for LOBS and/or an exaggerated Flashback policy, you can set the value to 0.
    Last edited by ebrian; 06-01-08 at 03:46.

  3. #3
    Join Date
    Feb 2008
    Posts
    38
    what is the negative effect of setting undo_retention to high value?

  4. #4
    Join Date
    May 2006
    Posts
    132
    Well you'll have to be concerned with how large your UNDO tablespace could potentially grow, not to mention the size of the UNDO datafiles for B&R.

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