bank::vote_accounts returns a hash-map which is slow to iterate, but all uses only require an iterator: https://github.com/solana-labs/solana/blob/b3dc98856/runtime/src/bank.rs#L4300-L4306 Similarly, calculate_stake_weighted_timestamp takes a hash-map whereas it only requires an iterator: https://github.com/solana-labs/solana/blob/b3dc98856/sdk/src/stake_weighted_timestamp.rs#L21-L28