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  1. #1
    Join Date
    Aug 2011
    Posts
    46

    Unanswered: Bufferpool physical read greater than logical reads ?

    I have this formula to calculate bufferpool hit ratio:

    DEC((1 - (FLOAT(TOTAL_DATA_PHYSICAL_READS) / FLOAT(TOTAL_DATA_LOGICAL_READS))) * 100,5,2)

    Hypothetical question: is it possible, physical_reads could be greater than logical read resulting into negative hit ratio ?

  2. #2
    Join Date
    Jan 2009
    Location
    Zoetermeer, Holland
    Posts
    746
    Too much prefetching.

  3. #3
    Join Date
    Sep 2008
    Location
    Toronto,Canada
    Posts
    655
    Yes,

    Recently, I came across one database having Hit Ratio over 115 %.

    But,

    I wonder, do we need it to tune down ??



    Regards
    DBFinder

  4. #4
    Join Date
    Jun 2003
    Location
    Toronto, Canada
    Posts
    5,516
    Provided Answers: 1
    You may want to look at the unread prefetch pages metric. It may indicate that prefetching is too aggressive and you are reading more data from disk than you actually need, wasting I/O bandwidth.

  5. #5
    Join Date
    Sep 2008
    Location
    Toronto,Canada
    Posts
    655
    That makes sense !!

    Thanks

    DBFinder

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