%% @doc What's stored in the database.
%% 'index' is the primary key, 'hash' is also indexed.
-record(plop, {
          index :: non_neg_integer(),           % Primary key.
          hash :: binary(),          % Hash over #plop_entry{} in mtl.
          mtl :: mtl(),              % Merkle Tree Leaf.
          spt :: spt()               % Signed Plop Timestamp.
         }).