# Oracle bitmap indexes
With Amazon DMS, you can optimize query performance for data warehousing and ad-hoc queries by creating Oracle bitmap indexes. You can use bitmap indexes to enhance the speed of complex queries involving conditions, joins, and aggregations on columns with a relatively small number of distinct values. Bitmap indexes can significantly improve query response times, especially for star schema queries common in data warehousing and business intelligence applications.
| Feature compatibility | Amazon SCT / Amazon DMS automation level | Amazon SCT action code index | Key differences |
| --- | --- | --- | --- |
|  |  | [Indexes](chap-oracle-aurora-mysql.tools.actioncode.md#chap-oracle-aurora-mysql.tools.actioncode.indexes) | MySQL doesn’t support BITMAP index. |
## Oracle usage
Bitmap indexes are task-specific indexes best suited for providing fast data retrieval for OLAP workloads and are generally very fast for read-mostly scenarios. However, bitmap indexes don’t perform well in heavy DML or OLTP workloads.
Unlike B-tree indexes where an index entry points to a specific table row, a bitmap index stores a bitmap for each index key.
Bitmap indexes are ideal for low-cardinality data filtering where the number of distinct values in a column is relatively small.
### Example
Create an Oracle bitmap index.
```
CREATE BITMAP INDEX IDX_BITMAP_EMP_GEN ON EMPLOYEES(GENDER);
```
For more information, see [CREATE INDEX](https://docs.oracle.com/database/121/SQLRF/statements_5013.htm#SQLRF01209) in the *Oracle documentation*.
## MySQL usage
Currently, Amazon Aurora MySQL doesn’t provide a comparable alternative for bitmap indexes.