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What is the correct behavior of the Paxos agent in this scenario?

I look at Paxos, and I am confused about how the algorithm should behave on this contrived example. I hope the diagram below explains the scenario.

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A few points:

  • Each agent acts as an initiator / acceptor / student
  • Prepare messages have the form (instance, proposal_num)
  • Suggested messages are in the form (instance, proposal_num, proposal_val)
  • Server1 and Server2 both decide to start the application process at the same time
  • At the beginning, messages M1, M2 and M3 occur simultaneously

It seems that although the protocol is "correct", i.e. only one value is selected S2, Server1 and Server2 believe that it was selected due to different offer numbers.

Is only the Paxos algorithm executed when a message is Decide(...)sent to students? I must have misunderstood that Paxos Made Simple, but I thought the choice was made when the developers reached a quorum for their posts Propose(...).

If the choice is made only after the message has been Decide(...)sent to the agents, should Server2 stop sending Decide(1, 5, S2)when it is being restored because it has seen a later one Prepare(1, 7)?

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2 answers

Just reformulate the terms (let it also throw 1, because we are considering only one iteration of Paxos):

1) Offer (n) == offer (n) a message from the creator with the current identifier n

2) AcceptPrepare (n, v) == ack (n, v), , n. v , node , o.w. v

3) CreateDecide (n, v) == accept! (x, v), x. , prepare (n), n > x

(n), - n accept! (n, v). (n + x), x > 0, ​​ n + x - - ack (n, v) accept! ( n, v), , , n + x, x > 0 (AKA, accept! (n, v))

, accept! (n, v), .

, server2 accept! (5, S2), , 5 < 7.

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, node , ( AcceptPropose ), , . Decide , , node , .

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, , : , , , , , ? , , : , , - , , , , .

:

, accept! (n, v), .

-, AcceptPropose. Promises, Propose messsages /. AcceptPropose .

-, , AcceptPropose. , , node AcceptPropose , , . , AcceptPropose / Decided, , .

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