How does PostgreSQL compare to VoltDB? I'm trying to get a handle on the different databases, and VoltDB sounds exciting, but everyone's talking about PostgreSQL. Then there's Mnesia which I hear is, as all things Erlang, excellent, though it's kinda tied to Erlang. I know it's hard to say what's best, but what would you say is the best DB for a completely new multilingual project that needs throughput but prioritize…
WhatsApp I hear uses Mnesia. If you use Erlang and can fit everything in memory that does look pretty nice. It integrates right into the language.
This isn't necessarily a bad thing; it's a very easy model to reason about, it rarely has an issue if your cluster doesn't span more than one data center, and it lets you know when it happens via events you can subscribe to. But doing anything different, up to and including healing the partition automatically, is left to the user.
There's also a few warts due to its history; disc only tables have a rather small max size (so if you're not expecting everything to be stored in RAM as well, you don't want to use Mnesia), indexes are shockingly inefficient for writes, and a few other odds and ends that I don't really remember. For persisted, but fast, storage in Erlang, where partitions aren't common, it's great, but outside of those sorts of use cases there's probably something better.