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Range of extents in an IAM

  • November 5, 2005 at 11:02 am

    #166620

    Hi,

    Could somebody please tell me what the term "range of extents" in the context of an IAM bitmap means? I do understand that in the bitmap each bit represents one extent. What I don't know or understand is does an IAM try to cover all the extents in the database, and when you don't have enough space in the IAM, another IAM is allocated to represent all the extents in the database? Or is the range based on some other basis?

    I would appreciate if someone shed some light on this issue.

    Karim

  • November 5, 2005 at 4:14 pm

    #602529

    Each object has at least one IAM for each file on which it has extents.

    An IAM page is 8K bytes which is 65536 bits ( 8 * 1024 bytes * 8 bits). Each bit tracks where the extent is used by the object. The bit is true (1) when the object is using that extent, otherwise false (0).

    One extent is 8 pages at 8K or 64K.

    So one IAM page can track 65536 * 64 * 1024 / (1024 * 1024 ) = 4096 Mb or 4Gb.

    So when a file exceeds 4Gb, then for each object in the extents over 4Gb, a new IAM page must be created within that file.

    SQL = Scarcely Qualifies as a Language

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