I&#x27;m also in a similar position where I&#x27;d like to store approximately 560k records &#x2F; user &#x2F; year. My understanding is that Cassandra doesn&#x27;t support some useful queries that would be useful when business logic is less clear (like group by)[1]. I&#x27;m leaning towards using PostgreSQL with a dedicated write DB until performance becomes an issue.<p>[1] <a href="http:&#x2F;&#x2F;stackoverflow.com&#x2F;questions&#x2F;17342176&#x2F;max-distinct-and-group-by-in-cassandra" rel="nofollow">http:&#x2F;&#x2F;stackoverflow.com&#x2F;questions&#x2F;17342176&#x2F;max-distinct-and...</a>