Optimiser
DBAsupport.com Forums - Powered by vBulletin
Results 1 to 5 of 5

Thread: Optimiser

  1. #1
    Join Date
    Jun 2001
    Location
    Dublin, Ireland
    Posts
    66
    I have a large database. The optimiser is currently set to 'RULE'.
    Should I be using the cost based optimiser?
    I would be grateful if anyone could explain a bit more about the optimiser or point me to some relevant links or articles on this subject.

    Thanks in advance.

  2. #2
    Join Date
    Apr 2002
    Location
    Germany.Laudenbach
    Posts
    448

    Exclamation

    Hello;
    If you switch the Optimizer to CHOOSE then never, never collect statistics for every Table.
    You will wonder but the CBO in some Cases decreases the perfomance.
    Go table by table and most by tables you like to use features which needs CBO;
    The CBO is not bad but you have to think a lot how you create the statitistics, when to create histograms, when to compute when to estimate, how often per week/month ...

    Orca

  3. #3
    Join Date
    Dec 2001
    Location
    USA
    Posts
    620
    Hi Orca777,

    That's interesting. How to decide which tables should be analyzed and which should be not.

    I presently have RULE defined in init.ora but still analyzes all my schema tables and then use CBO hints in queries.

    Is this OK?

    Thanks,

    Sam
    ------------------------
    To handle yourself, use your head. To handle others, use your heart

  4. #4
    Join Date
    Jun 2001
    Location
    Dublin, Ireland
    Posts
    66
    Hi Sam
    What happens when you analyse tables?
    Can you give me some example of how to use a CBO hint in a query.

  5. #5
    Join Date
    Apr 2002
    Location
    Germany.Laudenbach
    Posts
    448
    Hello samdba;

    i think your way is the best!
    So the (professional) SQL-Developer can decide with a Hint when to use CBO.
    The only thing is that you define an analyze-Subsystem which anlyze the objects for you in a CPU-NonWaisting and exact way.

    Orca

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  



Click Here to Expand Forum to Full Width