Apache cassandra is a distributed database for managing large amounts of structured data across many commodity servers, while providing highly available service and no single point of failure.
The archichecture is purely based on the cap theorem, which is availability , and partition tolerance, and interestingly eventual consistently.
Dont Use it, if your not storing volumes of data across racks of clusters,
Dont use if you are not storing Time series data,
Dont Use if you not patitioning your servers,
Dont use if you require strong Consistency.