As a DBA, I can say that it takes 5 to 10 years for a new database or file system to be ready (reliable, few global mutexes, third-party tools, programming language support, etc.) for production with paid customers.

So you should be using MySQL or Postgres for the Source of Truth (SoT) and things like Cassandra or CockroachDB for specialized use cases (caches, end-user metrics with TTL, etc.) But I would never put important data in a distributed database since there's too many moving parts and it's impossible to verify if the input matches the output over a decade.

If you need multi-master for failover today, I would pick Percona XtraDB Cluster (I've used it in production for 5 years) or MySQL 8.

https://dev.mysql.com/doc/refman/8.0/en/group-replication-mu...

If you don't have paying clients, then it really doesn't matter what tools you choose.

An example of the above is MongoDB, irrationally beloved by HN. Until recently it had a global write mutex and a POS (myisam-class) storage engine. After most companies migrated off of it for production, there are two Innodb-class storage engines now (native and WiredTiger) that add credibility ... after a decade of data loss and poor write performance. Those new engines will be ready for heavy-duty use in ... about 5 years.