Allow it for (*Trie).Put. And distinguish empty value and nil value for
(*Trie).PutBatch, because batch is already capable of handling both nil
and empty value. For (*Trie).PutBatch putting nil value means deletion,
while putting empty value means just putting LeafNode with an empty
value.
We use them quite frequently (consider children for a new branch
node) and it is better to get rid of unneeded allocations.
Signed-off-by: Evgeniy Stratonikov <evgeniy@nspcc.ru>
This is not a problem in practice, as all keys are prefixed
by a contract ID. However in theory it can lead to a different
state root after new portion of changes thus this fix.
Because trie size is rather big, it can't be stored in memory.
Thus some form of caching should also be implemented. To avoid
marshaling/unmarshaling of items which are close to root and are used
very frequenly we can save them across the persists.
This commit implements pruning items at the specified depth,
replacing them by hash nodes.
Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>
MPT is a trie with a branching factor = 16, i.e. it consists of sequences in
16-element alphabet.
Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>
