Agree w/ all these points (forgot "S3 has provider lock-in" though others replicate the API). I do use Cassandra for most use cases and I don't hit GC things, but I understand the concerns that come with the JVM (no, haven't subbed Scylla in yet). One that I haven't tried but want to hear the downsides of is https://github.com/pingcap/tikv (not the DB built on top, but just that one for KV). A nice published list of all cons of all database systems would be ideal.