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question on index

  • November 24, 2012 at 10:35 am

    #271151

    have a question about non-clustered indexes

    when a RID lookup is being performed, does the query optimizer need to go via the IAM map to know where the data is in the heap, or can it go directly to the data?

  • November 24, 2012 at 10:48 am

    #1561985

    It can go straight to the data. The RID is a 8-byte combination of file ID, page number and slot array. The first 2 allow SQL to go straight to the page, the last identifies where on the page the row in question can be found.

    Gail Shaw
    Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
    SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

    We walk in the dark places no others will enter
    We stand on the bridge and no one may pass

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