We're trying to determine which type of index (B-tree, Bitmap, etc..) would be better for an attribute that will only to values of either "Y" or "N" on a table that has 3.5 million records and growing. We are estimating an average of 500K with value of "N", the rest "Y".
We have a Data Warehouse that updates once a day with batch processing. There is a cursor that processes the table with 3.5 million records and it is using sequential scan and not the associated binary index because of NULLS in one of the concatenated indexed columns.
Given this, is BITMAP still the best and most efficient type of index we can use?