BITMAP Versus B-TREE

DBA fellas,

I have seen better query performance after converting two indexes to
bitmap, for few warehouse queries. I have got around 50 other indexes,
like

SELECT index_name,TABLE_NAME,DISTINCT_KEYS,NUM_ROWS,DISTINCT_KEYS/NUM_ROWS
FROM dba_indexes
WHERE owner='ABCD' AND num_rows != 0 AND DISTINCT_KEYS/NUM_ROWS < 0.01
ORDER BY 5  ;

There is a couple of indexes with 1 distinct key and 1Million rows. Im
sure they are good candidates for Bitmap.. but I think bitmaps have
downsize on DML and row locking for updates..  I hope someone here
would have some SWEET or SOUR experiences with Bitmaps. Would you
please share ?

Thanks
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