Re: bitmap conversion to rowids operation with btree indexes?

Yes

If you check the plan you should see things like: table access by rowid

    bitmap conversion to rowid

        bitmap and                    -- could be OR
            bitmap conversion (from rowids)
                sort (order by)
                    index (range scan) of {btree index}
            bitmap conversion (from rowids)
                sort (order by)
                    index (range scan) of {btree index}

Oracle can do this on tables without bitmap indexes if parameter b_tree_bitmap_plans = true.

If the parameter is false, the manual says (I think) that there has to be at least one bitmap index in existence for this to be possible.

The default value is FALSE in 8i, and true in 9i, and some people have reported performance problems because there setup started doing this conversion too frequently in inappropriate cases.

Regards

Jonathan Lewis

http://www.jlcomp.demon.co.uk/faq/ind_faq.html The Co-operative Oracle Users' FAQ

http://www.jlcomp.demon.co.uk/seminar.html Public Appearances - schedule updated Dec 23rd 2004

• Original Message ----- From: <ryan_gaffuri_at_comcast.net> To: <oracle-l_at_freelists.org> Sent: Tuesday, January 11, 2005 3:54 PM Subject: bitmap conversion to rowids operation with btree indexes?

I see this operation in plans occasionally when I'm using btree indexes and there are not any bitmaps. I also see:
BITMAP OR when using 2 btree indexes in the plan.

does oracle do some conversion to bits to optimize certain plans even without bitmap indexes?

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http://www.freelists.org/webpage/oracle-l Received on Tue Jan 11 2005 - 10:07:56 CST