Bitmap index: A type of index that uses a string of bits to quickly locate rows in a table. Bitmap indexes are normally used to index low cardinality columns in a warehouse environment.
Btree index: A type of index that uses a balanced tree structure for efficient record retrieval. B-tree indexes store key data in ascending or descending order.
Difference Between B-Tree Index & Bitmap Index:
1. B-tree Index has High cardinality values(usually when we have repeated columns), where as Bitmap Index has Low Cardinality values(usuall when column have few values like true/false). 2. B-tree Index is userful for OLTP, where as Bitmap Index is useful for Dataware Housing. 3. B-tree index updates on key values has relatively inexpensive, where as Bitmap index has more expensive.
Bitmap indexes are more advantageous than b-tree indexes when the table has millions of rows and the key columns have low cardinality. bitmap indexes provide better performance than b tree indexes when queries often use a combination of multiple where conditions involving the OR operator, the table is read-only, or when there is low update activity on the key columns.