Clarifying the Flight case

[lookfwd]

Really great talk on JOTB17, and there was this question on the flight case and idempotency VS commutativity but the explanation wasn't very clear. I think that we need a little diagram or example or test that clarifies what happens in this case. e.g.

                          | Flight Went Through    | Flight Didn't go Through |
                          ----------------------------------------------------|
I do commit & do cancel   | have two bookings, one | Will have an extra add   |
                          | cancel, if the first   | and remove but yes - the |
                          | booking goes after the | system is hapilly        |
                          | 1st cancel, there's no | correct so +1            |
                          | reason to not go       |                          |
                          | through thus ending    |                          |
                          | in a booked state. The |                          |
                          | only solution here,    |                          |
                          | would be to have       |                          |
                          | monotonic IDs for      |                          |
                          | the booking orders     |                          |
                          | which means            |                          |
                          | serialization. This    |                          |
                          | then should be a       |                          |
                          | necessary and          |                          |
                          | explicit requirement   |                          |
                          | because that system    |                          |
                          | can't be CA and would  |                          |
                          | add significant        |                          |
                          | latency and be a       |                          |
                          | single point of at     |                          |
                          | least partial failure. |                          |