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Use effective balances to determine column custody #4218

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Mar 28, 2025
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Use effective balances to determine column custody #4218

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17 changes: 9 additions & 8 deletions specs/fulu/validator.md
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Original file line number Diff line number Diff line change
Expand Up @@ -48,7 +48,7 @@ document and used throughout.
| Name | Value | Description |
| - | - | - |
| `VALIDATOR_CUSTODY_REQUIREMENT` | `8` | Minimum number of custody groups an honest node with validators attached custodies and serves samples from |
| `BALANCE_PER_ADDITIONAL_CUSTODY_GROUP` | `Gwei(32 * 10**9)` | Balance increment corresponding to one additional group to custody |
| `BALANCE_PER_ADDITIONAL_CUSTODY_GROUP` | `Gwei(32 * 10**9)` | Effective balance increment corresponding to one additional group to custody |

## Helpers

Expand Down Expand Up @@ -108,15 +108,15 @@ A node with validators attached downloads and custodies a higher minimum of cust
determined by `get_validators_custody_requirement(state, validator_indices)`. Here, `state` is the
current `BeaconState` and `validator_indices` is the list of indices corresponding to validators
attached to the node. Any node with at least one validator attached, and with the sum of the
balances of all attached validators being `total_node_balance`, downloads and custodies
effective balances of all attached validators being `total_node_balance`, downloads and custodies
`total_node_balance // BALANCE_PER_ADDITIONAL_CUSTODY_GROUP` custody groups per slot, with a minimum
of `VALIDATOR_CUSTODY_REQUIREMENT` and of course a maximum of `NUMBER_OF_CUSTODY_GROUPS`. The node
SHOULD dynamically adjust its custody groups following any changes to the balances of attached
validators.
SHOULD dynamically adjust its custody groups following any changes to the effective balances of
attached validators.

```python
def get_validators_custody_requirement(state: BeaconState, validator_indices: Sequence[ValidatorIndex]) -> uint64:
total_node_balance = sum(state.balances[index] for index in validator_indices)
total_node_balance = sum(state.validators[index].effective_balance for index in validator_indices)
count = total_node_balance // BALANCE_PER_ADDITIONAL_CUSTODY_GROUP
return min(max(count, VALIDATOR_CUSTODY_REQUIREMENT), NUMBER_OF_CUSTODY_GROUPS)
```
Expand All @@ -125,9 +125,10 @@ This higher custody is advertised in the node's Metadata by setting a higher `cu
and in the node's ENR by setting a higher `custody_group_count`. As with the regular custody
requirement, a node with validators MAY still choose to custody, advertise and serve more than
this minimum. As with the regular custody requirement, a node MUST backfill columns when syncing. In
addition, when the validator custody requirement increases, due to an increase in the total balance
of the attached validators, a node MUST backfill columns from the new custody groups. However, a
node MAY wait to advertise a higher custody in its Metadata and ENR until backfilling is complete.
addition, when the validator custody requirement increases, due to an increase in the total
effective balance of the attached validators, a node MUST backfill columns from the new custody
groups. However, a node MAY wait to advertise a higher custody in its Metadata and ENR until
backfilling is complete.

*Note:* The node SHOULD manage validator custody (and any changes during its lifetime) without any
input from the user, for example by using existing signals about validator metadata to compute the
Expand Down