[zzzcpan]

> That function can do whatever it wants, including any number of reads, writes, and arbitrary logic based on the reads. But critically, it can't talk back to the calling client, except for to send the final result.

If that function can still do everything the client did and the client still has to wait for a transaction - you are only eliminating interactive communications overhead, not actually improving or simplifying anything fundamentally. There is still consensus, coordination happening during that waiting and all of this is still fundamentally incompatible with computers spread across the globe communicating over unreliable links.

What would actually be a big improvement is eliminating waiting for coordination, but would require some change in programming model [1].

> The Calvin way is so much easier, it seems like there must be some very good reason that it's not what CockroachDB does.

It's just not "so much easier", that's the reason.

[1] https://arxiv.org/pdf/1901.01930.pdf