explain plan output different
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Thread: explain plan output different

  1. #1
    Join Date
    Oct 2003
    Posts
    312

    explain plan output different

    Hi all,

    if the table structure is the same and index the same, another word, two schema are the same, what could make the plan execute different???

    I know the anylyze is one and what are the others?????

    thanks

  2. #2
    Join Date
    Apr 2003
    Location
    South Carolina
    Posts
    148
    -- The number of rows in the tables ...
    -- The "Browning" of indexes (ie, deletes that have occurred leaving
    index rows marked for delete).
    -- The "Skewness" of the indexes (I believe that Oracle will prefer
    a table scan if the index will return more than 12% or so of the data) (Histograms ... ex: index has 100 rows with 5 distinct values - 20% of the rows ... if the data is skewed in such that 90 of the rows are of 1 value ... Oracle needs to know this..

    HTH
    Gregg

  3. #3
    Join Date
    Oct 2003
    Posts
    312
    thanks Greg,

    what if the number of rows are different, what could you do for it to pick up the index???

    could you please refer to my other thread about the query it didn't pick up the index and give me some advise???

    thanks

  4. #4
    Join Date
    Oct 2002
    Posts
    807
    what if the number of rows are different, what could you do for it to pick up the index???
    If all fails, use hints. Not good practise though.

    PS : RTM about different optimizers.

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