Re: bitmap conversion to rowids operation with btree indexes?
- From: "Jonathan Lewis" <jonathan@xxxxxxxxxxxxxxxxxx>
- To: <ryan_gaffuri@xxxxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Tue, 11 Jan 2005 16:12:23 -0000
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@xxxxxxxxxxx>
To: <oracle-l@xxxxxxxxxxxxx>
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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