Always use a relational database. Make sure to use one that supports recursive queries, and that doesn't suck. If you need to shard your database, do that. F

Always use a relational database. Make sure to use one that supports recursive queries, and that doesn't suck. If you need to shard your database, do that. For example, say you're building a ridesharing app. You'll have databases of users and drivers, but you can totally shard the driver DB by city, and even the user DB can be sharded this way (copying into a shard an entry from a main truth db). The DB of available cars and rides can be in-memory only -- if you lose it you can let the client-side apps drive recovery. You can use things like FDW to get a view that looks like a single DB, and then you can write queries purely in SQL. Look ma', no hand-coded joins and such.