If you are not familiar, DB-engines.com keeps a listing of who the major players are in the database world.

https://db-engines.com/en/ranking

MongoDB is ranked #5 on the list at present; Cassandra comes in at #11. (And Scylla, which they moved to most of their workload from Cassandra, is currently #88.)

DB-engines also have specific rankings for what are known as 'NoSQL wide column stores' — which is what Cassandra and Scylla are classed as:

https://db-engines.com/en/ranking/wide+column+store

Note that MongoDB is a different class of NoSQL entirely. It is a "document store" — MongoDB is the most popular document store.

https://db-engines.com/en/ranking/document+store

But what this means is that even though both MongoDB, Cassandra and Scylla are all "NoSQL" making this move for Discord required significant data modeling and migration.

(Note that the difference between Cassandra and Scylla is far narrower. Both use the same data model and Cassandra Query Language (CQL).

Hope that helps give you some orientation in the NoSQL database field.

This is excellent. Thank you!

Scylla, for one. Which is mentioned as a possible "next step" in the article.