state machine cleanup
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Jae Kwon
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9e1794eaea
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4d5fda7516
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@ -5,59 +5,64 @@ Consensus State Machine Overview:
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* NewHeight, NewRound, Propose, Prevote, Precommit represent state machine steps. (aka RoundStep).
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* To "prevote/precommit" something means to broadcast a prevote/precommit vote for something.
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* During NewHeight/NewRound/Propose/Prevote/Precommit:
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* Nodes gossip the locked proposal, if locked on a proposal.
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* Nodes gossip the proposal proposed by the designated proposer for that round.
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* Nodes gossip the proposal block proposed by the designated proposer for that round.
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* Nodes gossip prevotes/precommits for rounds [0...currentRound+1] (currentRound+1 for catch-up)
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* Nodes also gossip prevotes for the proposal's POL (proof-of-lock) round if proposed.
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* Upon each state transition, the height/round/step is broadcast to neighboring peers.
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* The set of +2/3 of precommits from the same round for a block "commits the block".
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* The set of +2/3 of precommits at the same round for the same block is called a Commit, or Validation.
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* A block contains the last block's Validation, which includes the Commit precommits.
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While all the precommits in the Validation are from the same height & round (ordered by validator index),
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some precommits may be nil (if the validator's precommit vote didn't reach the proposer in time),
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or some precommits may be for different blockhashes for the last block hash (which is fine).
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* NewRound:
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* Set up new round. --> Then, goto Propose
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* NewRound(height:H,round:R):
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* Set up new round. --> goto Propose(H,R)
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* NOTE: Not much happens in this step. It exists for clarity.
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* Propose:
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* Propose(height:H,round:R):
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* Upon entering Propose:
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* The designated proposer proposes a block.
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* The designated proposer proposes a block for (H,R).
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* The Propose step ends:
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* After `timeoutPropose` after entering Propose. --> Then, goto Prevote
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* After receiving proposal block and POL prevotes are ready. --> Then, goto Prevote
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* After any +2/3 prevotes received for the next round. --> Then, goto Prevote next round
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* After any +2/3 precommits received for the next round. --> Then, goto Precommit next round
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* After +2/3 precommits received for a particular block. --> Then, goto Commit
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* After `timeoutPropose` after entering Propose. --> goto Prevote(H,R)
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* After receiving proposal block and all POL prevotes. --> goto Prevote(H,R)
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* After any +2/3 prevotes received for (H,R+1). --> goto Prevote(H,R+1)
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* After any +2/3 precommits received for (H,R+1). --> goto Precommit(H,R+1)
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* After +2/3 precommits received for a particular block. --> goto Commit(H)
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* Prevote:
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* Prevote(height:H,round:R):
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* Upon entering Prevote, each validator broadcasts its prevote vote.
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* If the validator is locked on a block, it prevotes that.
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* Else, if the proposed block from the previous step is good, it prevotes that.
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* Else, if the proposed block from Propose(H,R) is good, it prevotes that.
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* Else, if the proposal is invalid or wasn't received on time, it prevotes <nil>.
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* The Prevote step ends:
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* After +2/3 prevotes for a particular block or <nil>. --> Then, goto Precommit
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* After `timeoutPrevote` after receiving any +2/3 prevotes. --> Then, goto Precommit
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* After any +2/3 prevotes received for the next round. --> Then, goto Prevote next round
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* After any +2/3 precommits received for the next round. --> Then, goto Precommit next round
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* After +2/3 precommits received for a particular block. --> Then, goto Commit
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* After +2/3 prevotes for a particular block or <nil>. --> goto Precommit(H,R)
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* After `timeoutPrevote` after receiving any +2/3 prevotes. --> goto Precommit(H,R)
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* After any +2/3 prevotes received for (H,R+1). --> goto Prevote(H,R+1)
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* After any +2/3 precommits received for (H,R+1). --> goto Precommit(H,R+1)
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* After +2/3 precommits received for a particular block. --> goto Commit(H)
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* Precommit:
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* Precommit(height:H,round:R):
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* Upon entering Precommit, each validator broadcasts its precommit vote.
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* If the validator had seen +2/3 of prevotes for a particular block,
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* If the validator had seen +2/3 of prevotes for a particular block from Prevote(H,R),
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it locks (changes lock to) that block and precommits that block.
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* Else, if the validator had seen +2/3 of prevotes for nil, it unlocks and precommits <nil>.
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* Else, if +2/3 of prevotes for a particular block or nil is not received on time,
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* Else, if the validator had seen +2/3 of prevotes for <nil>, it unlocks and precommits <nil>.
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* Else, if +2/3 of prevotes for a particular block or <nil> is not received on time,
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it precommits what it's locked on, or <nil>.
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* The Precommit step ends:
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* After +2/3 precommits for a particular block. --> Then, goto Commit
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* After +2/3 precommits for <nil>. --> Then, goto NewRound next round
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* After `timeoutPrecommit` after receiving any +2/3 precommits. --> Then, goto NewRound next round
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* After any +2/3 prevotes received for the next round. --> Then, goto Prevote next round
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* After any +2/3 precommits received for the next round. --> Then, goto Precommit next round
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* After +2/3 precommits for a particular block. --> goto Commit(H)
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* After +2/3 precommits for <nil>. --> goto NewRound(H,R+1)
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* After `timeoutPrecommit` after receiving any +2/3 precommits. --> goto NewRound(H,R+1)
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* After any +2/3 prevotes received for (H,R+1). --> goto Prevote(H,R+1)
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* After any +2/3 precommits received for (H,R+1). --> goto Precommit(H,R+1)
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* Commit:
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* Commit(height:H):
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* Set CommitTime = now
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* Wait until block is received, then goto NewHeight
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* Wait until block is received. --> goto NewHeight(H+1)
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* NewHeight:
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* Upon entering NewHeight,
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* Move Precommits to LastCommit and increment height.
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* Wait until `CommitTime+timeoutCommit` to receive straggler commits. --> Then, goto NewRound round 0
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* NewHeight(height:H):
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* Move Precommits to LastCommit and increment height.
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* Set StartTime = CommitTime+timeoutCommit
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* Wait until `StartTime` to receive straggler commits. --> goto NewRound(H,0)
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* Proof of Safety:
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If a good validator commits at round R, it's because it saw +2/3 of precommits for round R.
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