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Replace committee exponential backoff with max progress #808

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merged 10 commits into from
Mar 26, 2019
Merged

Replace committee exponential backoff with max progress #808

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dd39d25
Replace committee exponential backoff with max progress
vbuterin Mar 19, 2019
db92235
Removed some no-longer-necessary functions
vbuterin Mar 19, 2019
c5ee74d
Justin fixes
vbuterin Mar 19, 2019
b50e148
Update 0_beacon-chain.md
JustinDrake Mar 19, 2019
d0c473d
Merge branch 'dev' into vbuterin-patch-18
vbuterin Mar 26, 2019
2c8e9a1
Merge branch 'dev' into vbuterin-patch-18
djrtwo Mar 26, 2019
cdbba3e
Merge branch 'vbuterin-patch-18' of github.com:ethereum/eth2.0-specs …
djrtwo Mar 26, 2019
a8410b8
add some attestation tests. fix genesi crosslink bug
djrtwo Mar 26, 2019
9fa6055
add more attestation tests
djrtwo Mar 26, 2019
2c5a68b
remove registry_change options from shuffling functions
djrtwo Mar 26, 2019
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122 changes: 25 additions & 97 deletions specs/core/0_beacon-chain.md
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Original file line number Diff line number Diff line change
Expand Up @@ -64,9 +64,7 @@
- [`split`](#split)
- [`get_epoch_committee_count`](#get_epoch_committee_count)
- [`get_shuffling`](#get_shuffling)
- [`get_previous_epoch_committee_count`](#get_previous_epoch_committee_count)
- [`get_current_epoch_committee_count`](#get_current_epoch_committee_count)
- [`get_next_epoch_committee_count`](#get_next_epoch_committee_count)
- [`get_crosslink_committees_at_slot`](#get_crosslink_committees_at_slot)
- [`get_block_root`](#get_block_root)
- [`get_state_root`](#get_state_root)
Expand Down Expand Up @@ -185,8 +183,10 @@ Code snippets appearing in `this style` are to be interpreted as Python code.
| `MAX_INDICES_PER_SLASHABLE_VOTE` | `2**12` (= 4,096) |
| `MAX_EXIT_DEQUEUES_PER_EPOCH` | `2**2` (= 4) |
| `SHUFFLE_ROUND_COUNT` | 90 |
| `MAX_CROSSLINK_EPOCHS` | `2**6` (= 64) |
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* For the safety of crosslinks `TARGET_COMMITTEE_SIZE` exceeds [the recommended minimum committee size of 111](https://vitalik.ca/files/Ithaca201807_Sharding.pdf); with sufficient active validators (at least `SLOTS_PER_EPOCH * TARGET_COMMITTEE_SIZE`), the shuffling algorithm ensures committee sizes of at least `TARGET_COMMITTEE_SIZE`. (Unbiasable randomness with a Verifiable Delay Function (VDF) will improve committee robustness and lower the safe minimum committee size.)
* `MAX_CROSSLINK_EPOCHS` should be a small constant times `SHARD_COUNT // EPOCH_LENGTH`

### Deposit contract

Expand Down Expand Up @@ -598,12 +598,7 @@ The types are defined topologically to aid in facilitating an executable version

# Randomness and committees
'latest_randao_mixes': ['bytes32', LATEST_RANDAO_MIXES_LENGTH],
'previous_shuffling_start_shard': 'uint64',
'current_shuffling_start_shard': 'uint64',
'previous_shuffling_epoch': 'uint64',
'current_shuffling_epoch': 'uint64',
'previous_shuffling_seed': 'bytes32',
'current_shuffling_seed': 'bytes32',

# Finality
'previous_epoch_attestations': [PendingAttestation],
Expand Down Expand Up @@ -826,20 +821,6 @@ def get_shuffling(seed: Bytes32,

**Note**: this definition and the next few definitions make heavy use of repetitive computing. Production implementations are expected to appropriately use caching/memoization to avoid redoing work.

### `get_previous_epoch_committee_count`

```python
def get_previous_epoch_committee_count(state: BeaconState) -> int:
"""
Return the number of committees in the previous epoch of the given ``state``.
"""
previous_active_validators = get_active_validator_indices(
state.validator_registry,
state.previous_shuffling_epoch,
)
return get_epoch_committee_count(len(previous_active_validators))
```

### `get_current_epoch_committee_count`

```python
Expand All @@ -849,25 +830,11 @@ def get_current_epoch_committee_count(state: BeaconState) -> int:
"""
current_active_validators = get_active_validator_indices(
state.validator_registry,
state.current_shuffling_epoch,
get_current_epoch(state),
)
return get_epoch_committee_count(len(current_active_validators))
```

### `get_next_epoch_committee_count`

```python
def get_next_epoch_committee_count(state: BeaconState) -> int:
"""
Return the number of committees in the next epoch of the given ``state``.
"""
next_active_validators = get_active_validator_indices(
state.validator_registry,
get_current_epoch(state) + 1,
)
return get_epoch_committee_count(len(next_active_validators))
```

### `get_crosslink_committees_at_slot`

```python
Expand All @@ -886,40 +853,27 @@ def get_crosslink_committees_at_slot(state: BeaconState,
next_epoch = current_epoch + 1

assert previous_epoch <= epoch <= next_epoch
committees_per_epoch = get_epoch_committee_count(get_active_validator_indices(
state.validator_registry,
epoch,
))

if epoch == current_epoch:
committees_per_epoch = get_current_epoch_committee_count(state)
seed = state.current_shuffling_seed
shuffling_epoch = state.current_shuffling_epoch
shuffling_start_shard = state.current_shuffling_start_shard
elif epoch == previous_epoch:
committees_per_epoch = get_previous_epoch_committee_count(state)
seed = state.previous_shuffling_seed
shuffling_epoch = state.previous_shuffling_epoch
shuffling_start_shard = state.previous_shuffling_start_shard
shuffling_start_shard = (
state.current_shuffling_start_shard - EPOCH_LENGTH * committees_per_epoch
) % SHARD_COUNT
elif epoch == next_epoch:
epochs_since_last_registry_update = current_epoch - state.validator_registry_update_epoch
if registry_change:
committees_per_epoch = get_next_epoch_committee_count(state)
seed = generate_seed(state, next_epoch)
shuffling_epoch = next_epoch
current_committees_per_epoch = get_current_epoch_committee_count(state)
shuffling_start_shard = (state.current_shuffling_start_shard + current_committees_per_epoch) % SHARD_COUNT
elif epochs_since_last_registry_update > 1 and is_power_of_two(epochs_since_last_registry_update):
committees_per_epoch = get_next_epoch_committee_count(state)
seed = generate_seed(state, next_epoch)
shuffling_epoch = next_epoch
shuffling_start_shard = state.current_shuffling_start_shard
else:
committees_per_epoch = get_current_epoch_committee_count(state)
seed = state.current_shuffling_seed
shuffling_epoch = state.current_shuffling_epoch
shuffling_start_shard = state.current_shuffling_start_shard
current_epoch_committees = get_current_epoch_committee_count(state)
shuffling_start_shard = (
state.current_shuffling_start_shard + EPOCH_LENGTH * current_epoch_committees
) % SHARD_COUNT

shuffling = get_shuffling(
seed,
generate_seed(state, epoch),
state.validator_registry,
shuffling_epoch,
epoch,
)
offset = slot % SLOTS_PER_EPOCH
committees_per_slot = committees_per_epoch // SLOTS_PER_EPOCH
Expand Down Expand Up @@ -1529,12 +1483,7 @@ def get_genesis_beacon_state(genesis_validator_deposits: List[Deposit],

# Randomness and committees
latest_randao_mixes=Vector([ZERO_HASH for _ in range(LATEST_RANDAO_MIXES_LENGTH)]),
previous_shuffling_start_shard=GENESIS_START_SHARD,
current_shuffling_start_shard=GENESIS_START_SHARD,
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previous_shuffling_epoch=GENESIS_EPOCH,
current_shuffling_epoch=GENESIS_EPOCH,
previous_shuffling_seed=ZERO_HASH,
current_shuffling_seed=ZERO_HASH,

# Finality
previous_epoch_attestations=[],
Expand Down Expand Up @@ -1574,7 +1523,6 @@ def get_genesis_beacon_state(genesis_validator_deposits: List[Deposit],
genesis_active_index_root = hash_tree_root(get_active_validator_indices(state.validator_registry, GENESIS_EPOCH))
for index in range(LATEST_ACTIVE_INDEX_ROOTS_LENGTH):
state.latest_active_index_roots[index] = genesis_active_index_root
state.current_shuffling_seed = generate_seed(state, GENESIS_EPOCH)

return state
```
Expand Down Expand Up @@ -1855,7 +1803,7 @@ def process_crosslinks(state: BeaconState) -> None:
total_balance = get_total_balance(state, crosslink_committee)
if 3 * participating_balance >= 2 * total_balance:
state.latest_crosslinks[shard] = Crosslink(
epoch=slot_to_epoch(slot),
epoch=min(slot_to_epoch(slot), state.latest_crosslinks[shard].epoch + MAX_CROSSLINK_EPOCHS),
crosslink_data_root=winning_root
)
```
Expand Down Expand Up @@ -2060,14 +2008,6 @@ def should_update_validator_registry(state: BeaconState) -> bool:
# Must have finalized a new block
if state.finalized_epoch <= state.validator_registry_update_epoch:
return False
# Must have processed new crosslinks on all shards of the current epoch
shards_to_check = [
(state.current_shuffling_start_shard + i) % SHARD_COUNT
for i in range(get_current_epoch_committee_count(state))
]
for shard in shards_to_check:
if state.latest_crosslinks[shard].epoch <= state.validator_registry_update_epoch:
return False
return True
```

Expand Down Expand Up @@ -2119,30 +2059,17 @@ def update_validator_registry(state: BeaconState) -> None:
Run the following function:

```python
def update_registry_and_shuffling_data(state: BeaconState) -> None:
# First set previous shuffling data to current shuffling data
state.previous_shuffling_epoch = state.current_shuffling_epoch
state.previous_shuffling_start_shard = state.current_shuffling_start_shard
state.previous_shuffling_seed = state.current_shuffling_seed
def update_registry(state: BeaconState) -> None:
current_epoch = get_current_epoch(state)
next_epoch = current_epoch + 1
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# Check if we should update, and if so, update
if should_update_validator_registry(state):
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update_validator_registry(state)
# If we update the registry, update the shuffling data and shards as well
state.current_shuffling_epoch = next_epoch
state.current_shuffling_start_shard = (
state.current_shuffling_start_shard +
get_current_epoch_committee_count(state) % SHARD_COUNT
)
state.current_shuffling_seed = generate_seed(state, state.current_shuffling_epoch)
else:
# If processing at least one crosslink keeps failing, then reshuffle every power of two,
# but don't update the current_shuffling_start_shard
epochs_since_last_registry_update = current_epoch - state.validator_registry_update_epoch
if epochs_since_last_registry_update > 1 and is_power_of_two(epochs_since_last_registry_update):
state.current_shuffling_epoch = next_epoch
state.current_shuffling_seed = generate_seed(state, state.current_shuffling_epoch)
# If we update the registry, update the shuffling data 2/3 or and shards as well
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state.current_shuffling_start_shard = (
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state.current_shuffling_start_shard +
get_current_epoch_committee_count(state) % SHARD_COUNT
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)
```

**Invariant**: the active index root that is hashed into the shuffling seed actually is the `hash_tree_root` of the validator set that is used for that epoch.
Expand Down Expand Up @@ -2397,7 +2324,8 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
# the attestation is trying to create
Crosslink(
crosslink_data_root=attestation.data.crosslink_data_root,
epoch=slot_to_epoch(attestation.data.slot)
epoch=min(slot_to_epoch(attestation.data.slot),
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attestation.data.previous_crosslink.epoch + MAX_CROSSLINK_EPOCHS)
)
}
assert state.latest_crosslinks[attestation.data.shard] in acceptable_crosslink_data
Expand Down