But for other problems such as distributed databases, you can't do joins across 2 geographically separated data centers That's where replication comes in as yo

But for other problems such as distributed databases, you can't do joins across 2 geographically separated data centers That's where replication comes in as your (arguably) most powerful weapon. I work with databases for, literally, decades and have never seen a successful implementation of two-phase-commits or joins on geographically distinct entities.