> Luckily, global orders are rarely needed and are easy to impose yourself (outside distributed cases): just let all involved parties synchronize with a common process.

When there are multiple agents/actors in a distributed system, and the timestamp resolution is datetime64, and clock synchronization and network latency are variable, and non-centralized resilience is necessary to eliminate single points of failure, global ordering is impractical to impossible because there is no natural unique key with which to impose a [partial] preorder [1][2]: there are key collisions when you try and merge the streams.

Just don't cross the streams.

[1] https://en.wikipedia.org/wiki/Preorder_(disambiguation)

[2] https://en.wikipedia.org/wiki/Partially_ordered_set

The C in CAP theorem is for Consistency [3][4]. Sequential consistency is elusive because something probably has to block/lock somewhere unless you've optimally distributed the components of the CFG control flow graph.

[3] https://en.wikipedia.org/wiki/Consistency_model

[4] https://en.wikipedia.org/wiki/CAP_theorem

FWIU, TLA+ can help find such issues. [5]

[5] https://en.wikipedia.org/wiki/TLA%2B