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Add notes about sync committee stability

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Alex Stokes 2021-05-07 10:06:44 -07:00
parent 86104ea361
commit 04a9595415
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6
specs/altair/beacon-chain.md
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@ -277,6 +277,9 @@ def get_sync_committee_indices(state: BeaconState, epoch: Epoch) -> Sequence[Val
"""
Return the sequence of sync committee indices (which may include duplicate indices)
for a given ``state`` and ``epoch``.
Note: This function is not stable during a sync committee period as
a validator's effective balance may change enough to affect the sampling.
"""
MAX_RANDOM_BYTE = 2**8 - 1
base_epoch = Epoch((max(epoch // EPOCHS_PER_SYNC_COMMITTEE_PERIOD, 1) - 1) * EPOCHS_PER_SYNC_COMMITTEE_PERIOD)
@ -310,6 +313,9 @@ def get_sync_committee(state: BeaconState, epoch: Epoch) -> SyncCommittee:
``SyncCommittee`` can also contain duplicate pubkeys, when ``get_sync_committee_indices``
returns duplicate indices. Implementations must take care when handling
optimizations relating to aggregation and verification in the presence of duplicates.
Note: This function should only be called at sync committee period boundaries, as
``get_sync_committee_indices`` is not stable within a given period.
"""
indices = get_sync_committee_indices(state, epoch)
pubkeys = [state.validators[index].pubkey for index in indices]