Switch to `BinaryTrie` state

What is wrong?

Shard chains use BinaryTrie for better efficiency. See https://github.com/ethereum/wiki/wiki/Wishlist#trie

How can it be fixed

1. Set BinaryTrie as the default trie of FlatTrieBackend.
2. Apply FlatTrieBackend in most sharding tests.

Will switch transaction trie and receipt trie in other tickets.

[NIC619]

The reason being is that different backends result in different state roots. So the original protocol will keep using NestedTrieBackend, the sharding one will only use FlatTrieBackend.

Ahh I see. I was under the wrong impression. If this is the case, then there won’t be a consensus failure problem.

And if sharing will only use FlatTrieBackend then I suppose we can just have touch_account raise NotImplementedError if used and remove the code that use it:

class ShardingComputation(BaseComputation):
    def apply_message(self):
        ...
        with self.vm_state.state_db() as state_db:
            state_db.touch_account(self.msg.storage_address)
        ...

[jannikluhn]

Yes, did this in https://github.com/ethereum/py-evm/pull/291