> we knew we were not going to use MongoDB sharding because it is complicated to use and not known for stability
But then goes on to describe using Cassandra and overcoming sharding and stability issues. I.e., changing the key, changing TTL knobs, adding anti-entropy sweepers, and considering switching to a different cassandra impl entirely.
Are these issues significantly harder to solve in MongoDB than Cassandra?
Cassandra and Scylla also use hinted handoffs so if a node is unavailable temporarily (up to a few hours) you can store "hints" for it when it comes back online. Handy for short admin windows.
Increasing top-end write throughput or replication in Cassandra is just adding more nodes, where in Mongo its not just adding nodes, its adding replica sets (which consist of 3 or more nodes). So there's a few more layers of complexity to that story. You need more replica sets to increase write throughput and need more nodes in replica sets to increase replication.
Im hand waving some details here, but I've worked with both platforms can definitely understand the choice at least from a pure infra lens.