Why is it generally ineffective to index a 'Low Cardinality' column like `Gender` ('Male'/'Female')?

1. A Standard B-Tree indexes are strictly limited to numeric identifiers and cannot store variable-length string data like `Gender` categories.
2. B If a query returns a large percentage of the table (>20%), a Sequential Scan is significantly faster than performing thousands of random index seeks.
3. C Low cardinality indexes consume a disproportionate amount of physical disk storage due to the way they handle internal page-filling policies.
4. D Filtering by low cardinality columns causes the database engine to acquire aggressive, table-level locks that frequently lead to application deadlocks.