The question is what matters and how big cardinality is.
1. MV updates are atomic
2. Updates on 2 tables are not. You'd require a logged batch to ensure
atomicity and so the write performance is also a little bit lower than
without batches
3. If you have a hand full of groups per user, collections
Hallöchen!
In RDBMS terms, I have a n:m relationship between "users" and
"groups". I need to answer the questions "who's in that group" and
"in which groups is he". In my Cassandra DB, this looks like this:
CREATE TABLE users (
id uuid PRIMARY KEY,
groups_member set
groups
