github.com/ari-anchor/sei-tendermint@v0.0.0-20230519144642-dc826b7b56bb/spec/consensus/proposer-based-timestamp/v1/pbts-algorithm_001_draft.md (about) 1 # PBTS: Protocol Specification (first draft) 2 3 This specification is **OUTDATED**. Please refer to the [new version][algorithm]. 4 5 ## Updated Consensus Algorithm 6 7 ### Outline 8 9 The algorithm in the [arXiv paper][arXiv] evaluates rules of the received messages without making explicit how these messages are received. In our solution, we will make some message filtering explicit. We will assume that there are message reception steps (where messages are received and possibly stored locally for later evaluation of rules) and processing steps (the latter roughly as described in a way similar to the pseudo code of the arXiv paper). 10 11 In contrast to the original algorithm the field `proposal` in the `PROPOSE` message is a pair `(v, time)`, of the proposed consensus value `v` and the proposed time `time`. 12 13 #### **[PBTS-RECEPTION-STEP.0]** 14 15 In the reception step at process `p` at local time `now_p`, upon receiving a message `m`: 16 17 - if the message `m` is of type `PROPOSE` and satisfies `now_p - PRECISION < m.time < now_p + PRECISION + MSGDELAY`, then mark the message as `timely` 18 19 > if `m` does not satisfy the constraint consider it `untimely` 20 21 22 #### **[PBTS-PROCESSING-STEP.0]** 23 24 In the processing step, based on the messages stored, the rules of the algorithms are 25 executed. Note that the processing step only operates on messages 26 for the current height. The consensus algorithm rules are defined by the following updates to arXiv paper. 27 28 #### New `StartRound` 29 30 There are two additions 31 32 - in case the proposer's local time is smaller than the time of the previous block, the proposer waits until this is not the case anymore (to ensure the block time is monotonically increasing) 33 - the proposer sends its time `now_p` as part of its proposal 34 35 We update the timeout for the `PROPOSE` step according to the following reasoning: 36 37 - If a correct proposer needs to wait to make sure its proposed time is larger than the `blockTime` of the previous block, then it sends by realtime `blockTime + ACCURACY` (By this time, its local clock must exceed `blockTime`) 38 - the receiver will receive a `PROPOSE` message by `blockTime + ACCURACY + MSGDELAY` 39 - the receiver's local clock will be `<= blockTime + 2 * ACCURACY + MSGDELAY` 40 - thus when the receiver `p` enters this round it can set its timeout to a value `waitingTime => blockTime + 2 * ACCURACY + MSGDELAY - now_p` 41 42 So we should set the timeout to `max(timeoutPropose(round_p), waitingTime)`. 43 44 > If, in the future, a block delay parameter `BLOCKDELAY` is introduced, this means 45 that the proposer should wait for `now_p > blockTime + BLOCKDELAY` before sending a `PROPOSE` message. 46 Also, `BLOCKDELAY` needs to be added to `waitingTime`. 47 48 #### **[PBTS-ALG-STARTROUND.0]** 49 50 ```go 51 function StartRound(round) { 52 blockTime ← block time of block h_p - 1 53 waitingTime ← blockTime + 2 * ACCURACY + MSGDELAY - now_p 54 round_p ← round 55 step_p ← propose 56 if proposer(h_p, round_p) = p { 57 wait until now_p > blockTime // new wait condition 58 if validValue_p != nil { 59 proposal ← (validValue_p, now_p) // added "now_p" 60 } 61 else { 62 proposal ← (getValue(), now_p) // added "now_p" 63 } 64 broadcast ⟨PROPOSAL, h_p, round_p, proposal, validRound_p⟩ 65 } 66 else { 67 schedule OnTimeoutPropose(h_p,round_p) to be executed after max(timeoutPropose(round_p), waitingTime) 68 } 69 } 70 ``` 71 72 #### New Rule Replacing Lines 22 - 27 73 74 - a validator prevotes for the consensus value `v` **and** the time `t` 75 - the code changes as the `PROPOSAL` message carries time (while `lockedValue` does not) 76 77 #### **[PBTS-ALG-UPON-PROP.0]** 78 79 ```go 80 upon timely(⟨PROPOSAL, h_p, round_p, (v,t), −1⟩) from proposer(h_p, round_p) while step_p = propose do { 81 if valid(v) ∧ (lockedRound_p = −1 ∨ lockedValue_p = v) { 82 broadcast ⟨PREVOTE, h_p, round_p, id(v,t)⟩ 83 } 84 else { 85 broadcast ⟨PREVOTE, h_p, round_p, nil⟩ 86 } 87 step_p ← prevote 88 } 89 ``` 90 91 #### New Rule Replacing Lines 28 - 33 92 93 In case consensus is not reached in round 1, in `StartRound` the proposer of future rounds may propose the same value but with a different time. 94 Thus, the time `tprop` in the `PROPOSAL` message need not match the time `tvote` in the (old) `PREVOTE` messages. 95 A validator may send `PREVOTE` for the current round as long as the value `v` matches. 96 This gives the following rule: 97 98 #### **[PBTS-ALG-OLD-PREVOTE.0]** 99 100 ```go 101 upon timely(⟨PROPOSAL, h_p, round_p, (v, tprop), vr⟩) from proposer(h_p, round_p) AND 2f + 1 ⟨PREVOTE, h_p, vr, id((v, tvote)⟩ 102 while step_p = propose ∧ (vr ≥ 0 ∧ vr < round_p) do { 103 if valid(v) ∧ (lockedRound_p ≤ vr ∨ lockedValue_p = v) { 104 broadcast ⟨PREVOTE, h_p, roundp, id(v, tprop)⟩ 105 } 106 else { 107 broadcast ⟨PREVOTE, hp, roundp, nil⟩ 108 } 109 step_p ← prevote 110 } 111 ``` 112 113 #### New Rule Replacing Lines 36 - 43 114 115 - As above, in the following `(v,t)` is part of the message rather than `v` 116 - the stored values (i.e., `lockedValue`, `validValue`) do not contain the time 117 118 #### **[PBTS-ALG-NEW-PREVOTE.0]** 119 120 ```go 121 upon timely(⟨PROPOSAL, h_p, round_p, (v,t), ∗⟩) from proposer(h_p, round_p) AND 2f + 1 ⟨PREVOTE, h_p, round_p, id(v,t)⟩ while valid(v) ∧ step_p ≥ prevote for the first time do { 122 if step_p = prevote { 123 lockedValue_p ← v 124 lockedRound_p ← round_p 125 broadcast ⟨PRECOMMIT, h_p, round_p, id(v,t))⟩ 126 step_p ← precommit 127 } 128 validValue_p ← v 129 validRound_p ← round_p 130 } 131 ``` 132 133 #### New Rule Replacing Lines 49 - 54 134 135 - we decide on `v` as well as on the time from the proposal message 136 - here we do not care whether the proposal was received timely. 137 138 > In particular we need to take care of the case where the proposer is untimely to one correct validator only. We need to ensure that this validator decides if all decide. 139 140 #### **[PBTS-ALG-DECIDE.0]** 141 142 ```go 143 upon ⟨PROPOSAL, h_p, r, (v,t), ∗⟩ from proposer(h_p, r) AND 2f + 1 ⟨PRECOMMIT, h_p, r, id(v,t)⟩ while decisionp[h_p] = nil do { 144 if valid(v) { 145 decision_p [h_p] = (v,t) // decide on time too 146 h_p ← h_p + 1 147 reset lockedRound_p , lockedValue_p, validRound_p and validValue_p to initial values and empty message log 148 StartRound(0) 149 } 150 } 151 ``` 152 153 **All other rules remains unchanged.** 154 155 Back to [main document][main_v1]. 156 157 [main_v1]: ./pbts_001_draft.md 158 159 [algorithm]: ../pbts-algorithm_002_draft.md 160 [algorithm_v1]: ./pbts-algorithm_001_draft.md 161 162 [arXiv]: https://arxiv.org/abs/1807.04938