> whatever shall you stamp when you should have one node on Earth and another on Mars?
Again, if you were familiar with the content of the papers, you could answer this yourself.
How it would work is establishing a phase locked loop between the oscillator on earth and the oscillator on mars, and then running a TrueTime style interval protocol. The downside of "Mars Spanner" is the very long round trip time would make the two phase commit protocol unacceptably long latency. However, the basic properties would still hold.
I don't know how else to explain it to you: a communicating distributed system can establish a single, canonical, total order on events. This is not a physical impossibility.
"Can establish a ... total order on events" is somewhat vacuous, the point is how it corresponds to the actual observed ordering. Otherwise you can just label arbitrarily, 1, 2, 3, ... that's also an ordering. I'm saying there is no such correspondence that is globally correct. It doesn't matter what protocol you run. You cannot synchronize two clocks that are apart. You can only synchronize them when they are in the same place.
I perfectly understand that with communication you can establish (read: impose) any arbitrary ordering you want and get nodes to agree to that. That's not really a useful resolution except in a narrow sense of "sometimes we really don't care about strict observed ordering," which may or may not be true.
The larger point is, Spanner doesn't solve any distributed database problem. It simply notices that on the timescale that today's workload appears to operate at, all the nodes can still be approximated as being collocated. There is, after all, a clock inside a computer as well, and this just extends it a little further.
Again, if you were familiar with the content of the papers, you could answer this yourself.
How it would work is establishing a phase locked loop between the oscillator on earth and the oscillator on mars, and then running a TrueTime style interval protocol. The downside of "Mars Spanner" is the very long round trip time would make the two phase commit protocol unacceptably long latency. However, the basic properties would still hold.
I don't know how else to explain it to you: a communicating distributed system can establish a single, canonical, total order on events. This is not a physical impossibility.