Active registry roots #1104
Active registry roots #1104
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Possible replacement of `latest_active_index_roots` with `latest_active_registry_roots` to allow for significantly more efficient light clients (see item 17 in #1054). Key changes: * Validator information (including indices) is pre-shuffled and grouped by committee. * Validator information relevant to light clients (`validator.effective_balance` and `validator.slashed`) is kept "close" to the validator index to avoid accessing `validator_registry`. * Validator information (`index`, `effective_balance`, `slashed`) is compactified into a `uint64` which is friendly to SSZ packing. * Shuffled pubkeys are available but kept separate from compact validator information. Light clients with pubkeys cached do not need to re-download and re-authenticate them.
specs/core/0_beacon-chain.md
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| shard = (get_start_shard(state, epoch) + committee_number) % SHARD_COUNT | ||
| for index in get_crosslink_committee(state, epoch, shard): | ||
| validator = validator_registry[index] | ||
| active_registry[shard].pubkeys.append(validator.pubkey) |
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You're sorting validators by their crosslink committee shard. This isn't going to be particularly useful for light clients unless we merge the two committees.
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That's a good point. Maybe we want to wait until phase 1 to put this light-client infrastructure in place.
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The active_index_roots in combination with the historical randaomixes being in state was generic enough to serve proofs about the historic crosslink and persistent committees.
If we go this new path, we should either wait or intend to put both committees in the registry root.
| validator = validator_registry[index] | ||
| committees[shard].pubkeys.append(validator.pubkey) | ||
| # index (top 7 bytes) + slashed (8th bit) + effective_balance (bottom 7 bits) | ||
| compact_validator = index << 8 + validator.slashed << 7 + validator.effective_balance // GWEI_PER_ETH |
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| compact_validator = index << 8 + validator.slashed << 7 + validator.effective_balance // GWEI_PER_ETH | |
| compact_validator = index << 8 + validator.slashed << 7 + validator.effective_balance // EFFECTIVE_BALANCE_INCREMENT |
Same value, but it might not be in other configurations / future. So let's use the increment constant instead.
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"pre-shuffling": could this simplify the spec more? I.e. we compute a list of shuffled active indices after the randao (or effectively the shuffling seed) is updated, and then just have the data (committees, active indices) available when we need it? Clients can already optimize it themselves, but it may actually reduce the spec complexity (if we can have this index list somewhere around...). |
We actually used to store the shuffling entirely in state, but after much debate removed it to (1) reduce state size and (2) give optionality to clients esp in resource restricted environments. |
JustinDrake
added
the
milestone:June 30 freeze 🥶
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Close in favour of #1219. |
Possible replacement of
latest_active_index_rootswithlatest_active_registry_rootsto allow for significantly more efficient light clients (see item 17 in #1054). Key changes:validator.effective_balanceandvalidator.slashed) is kept "close" to the validator index to avoid accessingvalidator_registry.index,effective_balance,slashed) is compactified into auint64which is friendly to SSZ packing.