They never return errors, so their interface should reflect that. This allows
to remove quite a lot of useless and never tested code.
Notice that Get still does return an error. It can be made not to do that, but
usually we need to differentiate between successful/unsuccessful accesses
anyway, so this doesn't help much.
Prevent
2021-03-27T00:05:23.382+0300 WARN blockQueue: failed adding block into the blockchain {"error": "error while trying to apply MPT changes: key not found", "blockHeight": 12757, "nextIndex": 12758}
after node restart (node reads "local" root hash that it doesn't have).
It was completely ruined by bf20db09e0. MPT was
updating bc.dao directly which shouldn't ever happen, it must write into the
same cache and then Persist these KVs as usual.
