Why are validator balances no longer part of ValidatorRecord?

[akhila-raju]

Validator_balances was separated into its own UInt64 array, rather than being part of ValidatorRecord. What was the thought process behind this decision?

'validator_registry': [ValidatorRecord],
'validator_balances': ['uint64']

[JustinDrake]

It's an optimisation to minimise the amount of hashing when computing the beacon state root. The validator_registry (which contains most of the state) changes slowly and requires little hashing effort to maintain. The validator_balances is a smaller part of the state with much higher churn, hence why it is segregated.

[akhila-raju]

Thank you!