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Getting costs for hypothetical query plans

  1. Getting costs for hypothetical query plans

    Hi,

    We have a query which has a surprising plan. I assume Oracle considered
    the right plan, but rejected it. Is there any way to tell it that plan,
    and have it tell me the cost breakdown of it? That would really help me
    figure out what's going wrong.

    Thanks,
    tom

    --
    Who would you help in a fight, Peter van der Linden or Bill Gates?

  2. Re: Getting costs for hypothetical query plans

    On Feb 25, 8:58*am, Tom Anderson wrote:
    > Hi,
    >
    > We have a query which has a surprising plan. I assume Oracle considered
    > the right plan, but rejected it. Is there any way to tell it that plan,
    > and have it tell me the cost breakdown of it? That would really help me
    > figure out what's going wrong.
    >
    > Thanks,
    > tom


    Sometimes the surprise is that Oracle is right.

    The way to force a plan is through the use of a complete set of
    hints. The performance guide in the docs has an introduction to that,
    and Jonathan Lewis has a Cost Based Optimizer book that explains in
    depth how it works, and there are many examples on his blog. Randolph
    shows you how to see what is going on and explains how to post a
    tuning request: http://oracle-randolf.blogspot.com/2...rformance.html
    Often just working through the steps answers the question.

    >
    > --
    > Who would you help in a fight, Peter van der Linden or Bill Gates?


    Neither, I'd run and get popcorn.

    jg
    --
    @home.com is bogus.
    "Risc and Itanium UNIX vendors again had a torrid three months, with
    revenues down 19.3% as the market was squeezed by x86 and System Z."
    Torrid? http://www.microscope.co.uk/news/ven...d-again-in-q4/

  3. Re: Getting costs for hypothetical query plans

    On Feb 25, 4:58*pm, Tom Anderson wrote:
    > Hi,
    >
    > We have a query which has a surprising plan. I assume Oracle considered
    > the right plan, but rejected it. Is there any way to tell it that plan,
    > and have it tell me the cost breakdown of it? That would really help me
    > figure out what's going wrong.


    Sounds like you want a 10053 CBO trace.
    http://asktom.oracle.com/pls/apex/f?...63445044804318
    http://tonguc.wordpress.com/2007/01/...053-trace-file



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