pub enum Note {
EpochRefused {
from: NodeId,
ts: u64,
why: Refusal,
},
ReportIgnored {
from: NodeId,
nts: u64,
why: Refusal,
},
ReachReported {
leader: NodeId,
nts: u64,
},
LeadershipYielded {
to: NodeId,
round: u64,
},
ProposalIgnored {
slot: u64,
},
WindowFull {
slot_in: u64,
slot_out: u64,
},
SlotReproposed {
slot: u64,
},
ProposalDisplaced {
slot: u64,
},
CollectedBelow {
slot: u64,
},
CaughtUpFrom {
slot: u64,
},
}Expand description
A decision a protocol took, in the vocabulary this stack narrates in.
Variants§
EpochRefused
An announcement of a new epoch was refused. The trace holds the refusal that went back on the wire; it does not hold what was wrong with the announcement.
ReportIgnored
A peer’s report of how far it had reached was not acted on. Nothing at all reaches the trace from this decision — it is the shape of silence that cost the most to diagnose.
ReachReported
This process volunteered how far it had reached to a leader that may never have been told it
had become one. The same NACK as a refusal goes on the wire, so the trace cannot tell the
two decisions apart; this says which it was.
LeadershipYielded
A leader was preempted by a higher ballot and did not take up another, because Ω no longer trusts it. Nothing at all reaches the trace from this decision — a leader that stops competing sends no message, sets no timer and raises no indication, so a run in which it correctly stood down and one in which it was never told apart look identical.
ProposalIgnored
A proposal was dropped because this leader already had one for the slot — Figure 7’s
if ∄c' : ⟨s, c'⟩ ∈ proposals, which is what keeps at most one commander per slot. The
decision produces no effect whatever.
WindowFull
A replica held requests it was not allowed to propose for, because slot_in had reached
slot_out + WINDOW — Invariant R5. Nothing at all reaches the trace from this decision:
a replica whose window is full sends nothing and looks exactly like one with nothing to do,
which is the shape the fourth liveness violation wears.
SlotReproposed
A proposal outstanding past its threshold was proposed again for the same slot — the replica’s half of Liu et al.’s fourth liveness fix. Where the leader is on this machine the proposal is a function call, so the repeat can reach the trace as nothing whatever; this says it happened, and the trace cannot tell it from a first proposal in any case.
ProposalDisplaced
A replica’s own command lost its slot to somebody else’s and went back into requests —
Figure 1’s if c'' ≠ c' then requests := requests ∪ {c''}. The decision produces no effect
until the command is proposed again at a later slot, and a replica that dropped it instead
would lose an append in silence.
CollectedBelow
State for every slot below slot was discarded, because enough replicas have applied it —
the source’s §4.2. Nothing at all reaches the trace from this decision: collecting sends
no message, sets no timer and raises no indication, so a run that collects and one that has
stopped collecting look identical from outside. Which matters, because stopping is the
specified behaviour when too few replicas remain to report.
CaughtUpFrom
A replica asked a peer for the decisions from slot onwards, because the consensus beneath
it has collected them and can no longer answer. Nothing at all reaches the trace from the
decision itself, and the request that follows is indistinguishable on the wire from any
other; this says why it was made.