Having used D1 in production - it's not very reliable. There was a comment on HN from one of D1 devs [1] saying that D1 is a sql wrapper on top of durable objects that mimicks sqlite distributed like nature.
> I'll let you in on a sort of dirty secret:
It's almost always better to use Durable Objects storage, rather than D1. Even if you only want a single global database, it's better to implement that as a singleton Durable Object, than by using D1. Because that's all D1 itself actually is: a singleton Durable Object that exposes an API to its SQLite database. It's just a wrapper.
> I'll let you in on a sort of dirty secret: It's almost always better to use Durable Objects storage, rather than D1. Even if you only want a single global database, it's better to implement that as a singleton Durable Object, than by using D1. Because that's all D1 itself actually is: a singleton Durable Object that exposes an API to its SQLite database. It's just a wrapper.
[1] https://news.ycombinator.com/item?id=48611834