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  • 15. Re: Bitmap index column goes for full table scan
    651776 Newbie
    Currently Being Moderated
    did you try a normal index? the bitmap is usefull for safe space when you have few values (is not your problem becuase the table is small), and because you can use more than one (with bitmap you can acces by the table by more than one index, with normal optimezer have to choose one, this is correct for you because you have one condition)

    did you collect statistics on the table?
  • 16. Re: Bitmap index column goes for full table scan
    Manik Expert
    Currently Being Moderated
    rp0428 wrote:
    >
    BITMAP indexes are created and are most appropriate for columns having low distinct values.
    >
    That MYTH has been busted for many years now by many people.

    See Richard Foote's series of articles about this myth and many others regarding indexes.
    http://richardfoote.wordpress.com/2010/02/18/myth-bitmap-indexes-with-high-distinct-columns-blow-out/
    >
    One of the great myths in Oracle is that bitmap indexes are only suitable and should only be used with columns that have so-called low cardinality (few distinct) values
    . . .
    >
    USED in DW is fine.. I am not arguing that..

    But learnt something from that link.. Thanks RP. This completely changed my view about BITMAP indexes.
    I like the last sentance there :
    The next time you unfortunately read that bitmap indexes should only be used with very “few” distinct values and would be “huge” otherwise, well hopefully you’ll appreciate that’s simply not correct.
    ;)

    I should have read thoroughly the documentation where it says :

    http://docs.oracle.com/cd/B28359_01/server.111/b28313/indexes.htm
    A gender column, which has only two distinct values (male and female), is optimal for a bitmap index. However, data warehouse administrators also build bitmap indexes on columns with higher cardinalities.
    Thanks for sharing!!!

    Cheers,
    Manik.
  • 17. Re: Bitmap index column goes for full table scan
    jeneesh Guru
    Currently Being Moderated
    34MCA2K2 wrote:
    I am sorry for being ignorant, can you please cite any scenario of locking due to bitmap indices? A link can be useful as well.
    Sorry for the late response. rp0428's post is clear enough for you to understand the issue.

    You could also go through this discussion at asktom : Bitmap indexes and locking
  • 18. Re: Bitmap index column goes for full table scan
    890271 Newbie
    Currently Being Moderated
    Thank you all for sharing your ideas. im little bit confused with this concepts . i will so through with the links shared.

    Thanks again for all.

    Edited by: 887268 on Apr 6, 2013 1:39 AM
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