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Thread: Extents

  1. #1
    Join Date
    Dec 2002
    Location
    Madrid - Spain
    Posts
    422
    Provided Answers: 1

    Angry Unanswered: Extents

    Hi,

    I need the formula to calculate the extents size and next entents size, and too I have a good performance in the comunication the two server.

    Thank you.

  2. #2
    Join Date
    Aug 2002
    Location
    Belgium
    Posts
    534
    There is no standard formula to calculate extent sizes.
    Just try to have the least extents as possible per table.
    The least number of extents give the best performance.
    rws

  3. #3
    Join Date
    May 2002
    Location
    Osnabrueck Germany
    Posts
    59
    Hi,
    thats what we learned
    page size(2048 or 4096 or ...)
    minus 24 (page header)
    minus 4 (page trailer)
    minus 56 (partition header)
    minus number of columns *4
    minus (number of keys *12) + (4 *number ob key parts)

    1.add 8 bytes to the length of key
    2.sum up all index entries
    3.add 25% to the sum from step 2
    4.guess the # of initial rows
    5.multiply the result of step3 by the number of rows from step4
    6.divide index space by 1024
    7.subtrac 32 from the page size
    8.sum up all column length in the row
    9.divide page size from step 7 by row length in the step 8 and round down to the greatest whole number.
    10.divide the number of rows from step 4 by the number of rows per page in step 9, round up.
    11.multipy the number of pages determined in step 10 by the size of a full page
    12.divide step 11 by 1024
    13.add the results of step 12 and step6

    estimate table growth
    14. guess the number of subsequent rows
    15.repeat steps 5-6 for index space and steps 10-13 for data space.
    use the estimate in step 14 as the number of rows in step 5 and 10.
    divide the final result by 7
    Juergen Ladwig

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