[rstuart4133]

> Not correct, but it's very easy to think timestamps will solve this. Timestamps aren't good because system times aren't synced across different computers precisely.

They can be. That's what Google Spanner does, using GPS and atomic clocks. It's not hard or expensive. An atomic clock + GPS will set you back under $1000 https://www.ebay.com/itm/174750548607 for one in a nice box, $200 for a PCB https://www.ebay.com/itm/353611628534. Apparently it gets you to with 1e-11, which is about 10 pico seconds (I think).

But that doesn't solve the problem. Lets say you have two event producers, and both produce two events at times t and t+1. Once they both arrive, it's trivial to process then in the right order. Your problem is there is an unreliable network connecting you to these producers. Those atomic clocks can guarantee those events t and t+1 are distinguishable events if they are just 10ps apart, but how long do you wait for t to arrive before you decide to process the event at t+1 because there was no event at t. I can absolutely guarantee you whatever time you decide is reasonable, the universe will at some point screw you over and drop the event occurring at on your doorstep just after you decided to process t1.

Your issue isn't that it's difficult, it's is you are living in a state of sin if you believe the problem solvable given the premises.

PS: Google Spanner doesn't attempt to do the impossible. In Spanners case there is a single event producer, and Spanner is "merely" trying to record the event consistently across multiple nodes. If there are multiple event producers then it will serialise them in some order, but if there are two disconnected, independent Spanners out there processing the same events from the same producers Google is not claiming there would decide on the same order. That would need a God more powerful than Google.