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Thread: Gathering Statistics

  1. #1
    Join Date
    Sep 2000
    Location
    Chennai, India
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    865
    Any known issues to be careful about when gathering statistics for the optimizer to use ?

    One thing I came across it not to generate stats for SYS. That's fine! When doing this for end users, any pitfalls to be careful about ? Can we rollback if application users face problems owing to this ?

    Thanks.

  2. #2
    Join Date
    Feb 2000
    Location
    Singapore
    Posts
    1,758
    You can not rollback but you can delete the statistics.

    Sanjay

  3. #3
    Join Date
    Sep 2000
    Location
    Chennai, India
    Posts
    865
    After using delete stats. . .

    Analyze < name> delete statistics;

    I will be in square one and appln. users will will be accessing their objects as if no stats. had been generated ?


  4. #4
    Join Date
    Feb 2000
    Location
    Singapore
    Posts
    1,758
    Yes!

    Sanjay

  5. #5
    Join Date
    Mar 2002
    Posts
    6
    You CAN rollback the statistics if gathering new stats makes your performance worse (it can!). But first you have to save them. Refer to the DBMS_STATS package about how to save statistics to a table so that you can reapply them if you need. In short order you want to
    1. Save stats to a stats table
    2. Delete stats (to clear out the histogram buckets)
    3. Analyze new stats.
    4. Do a sanity check to make sure you haven't made performance worse.

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