They should be used when:
- If the number of distinct values of a column is less than 1% of the number of rows in the table.
- If the values in a column are repeated more than 100 times, then the column is a candidate for a bitmap index.
- the table has LOW DML – You must have low insert./update/delete activity. Updating bitmapped indexes take a lot of resources, and bitmapped indexes are best for largely read-only tables and tables that are batch updated nightly.
Partition local and global indexes
We should always try to use local indexes on a partitioned table, except if the application strictly requires global ones (which is rear).