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  1. #1
    Join Date
    Jan 2008
    Posts
    88

    Unanswered: logical reads and physical reads

    Hi all,

    just a simple question for all. I am bit confused...is logical reads and physical reads are number of I/O or number of pages. If its I/O how to get average number of pages read per logical I/O or per Physical I/O

    Thanks
    Ajay

  2. #2
    Join Date
    Jan 2007
    Location
    Jena, Germany
    Posts
    2,721
    Logical/physical reads count the number of accesses to pages. Otherwise it would be named "logical I/O" or "physical I/O".

    A logical I/O happens if the page is already in the buffer pool. A physical I/O is comparable to a page fault at O/S level, i.e. the page has to be read from disk into the buffer pool before the caller can access the page.
    Knut Stolze
    IBM DB2 Analytics Accelerator
    IBM Germany Research & Development

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