
Banks have never heard of SYN/ACK - AndrewDucker
http://www.jwz.org/blog/2015/06/speaking-of-the-marvels-of-internet-commerce/
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Danack
From the fine article:

    
    
      1. Customer places an order.
      2. SYN: Can I charge $30?
      3. SYN/ACK: Yes.
      4. ACK + SYN: Do it.
      5. SYN/ACK: I am gonna do it.
      6. ACK: I see that you're gonna do it.
      

"If that was their model, then at no point does a communication failure cause
a charge to be in an ambiguous state. If I never get the message in #5, the
customer is not charged. If I get the message in #5 and my response in #6 is
not received, the customer is not charged."

Er.....that doesn't appear to solve anything, instead it just pushes the error
state down a level; there's still an ambiguous state where #6 is sent and not
received.

The client thinks the charge is going to take place, and so thinks the client
will be charged, but the bank never gets #6 and so never makes the charge, aka
distributed atomic operations are hard.

~~~
AndrewDucker
He doesn't say that the change makes things perfect - he says "There's only
one possible failure mode and not two, and that failure mode is the safer one"

