The thing I'm confused about is why migrating your production system onto a custom in-house data store (that you've written and you maintain) is easier / less work than migrating onto something you can use off the shelf which solves the problem you have.

I hear the argument that migrating from (say), postgres -> postgres + books is easier than moving everything into cockroachdb. But why is postgres + books easier than postgres + cockroach? The latter doesn't require you to write your own database from scratch. (And writing your own database is fun, so if you're doing it for that reason I understand, but thats not what the post says.)

Edit: Ah, I see - my confusion was because I missed the part which mentioned that this is just built on top of spanner. That makes sense!