How to start using histograms?
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  1. #1
    Join Date
    Oct 2002
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    Question How to start using histograms?

    Hi guys,

    I read some articles about histograms and a question that was posted here: link

    I really think that setting up the histograms could improve performance on larger tables, but the Oracle documentation isn't very clear on their explanation. So, I hope you guys can enlighten some questions I have.

    Here they are:
    1. Quote from "Oracle9i Database performance Tuning" ocp-book:
    Choosing the number of buckets for a histogram.
    If the number of frequently occurring distinct values in a column is relatively small, then set the number of buckets to be greater then that number.
    Okay, I get this, but how much bigger must that number be? Number of distinct values+1 or +2, +10?

    2. How do I determine the number of buckets, when the number of distinct values is bigger than the maximum number of buckets(254)?
    Do you make an estimated guess and test the results and increase/decrease the number and test again? I think analyzing all kinds of columns would take a lot of time and my production db has limited rest time.
    Can someone give me some guidelines on this?

    3. How big must a table be, before I can use column-histograms?
    (1000 rows? 10000 rows? 1 mln rows?)

    Any help, links or guidance are welcome...

    Erik
    Last edited by efrijters; 09-17-2003 at 05:54 AM.
    An expert is one who knows more and more about less and less until he knows absolutely everything about nothing.

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