[numbsafari]

It doesn’t exist. This isn’t how banks transfer funds between accounts.

It’s fake. As a result, you can’t actually evaluate the engineering trade offs of the proposed solution.

Here’s the thing: do you even need transactions (in the sense of ACID transactions that are resolved heuristically, as described in this article) between your microservices? Likely not.

And what are the implications of having to wait around for PGSQL and Mongo negotiate a transaction between a third data store? Probably blocking and latency and all the associated problems which will lead to … not use transaction across service boundaries.

[jen20]

The trick is to work out what you would do if you had to implement the entire system on paper in a 50s style office with triplicate carbon paper. Then do that, but with computers.

[yathaid]

That is not a trick, it is a false analogy. Two humans in eyesight line can be assured that they have exchanged messages successfully. Two computers cannot due to recursing acknowledgements (byzantine generals).

[defrost]

More realistically; Two humans in eyesight line can believe that they have exchanged messages successfully.

Both parties misunderstanding the other is a common trope in movies and novels for a reason.

[jen20]

No, it’s not a false analogy. Go look at an old office building and consider whether people really are “in eyesight line” - assuredly they are not.

The unreliable messaging links (internal mail) mean that resilience against missed messages and guards against not making progress must be built into the business process instead of an infrastructure layer.