anchor.diff:  -spec update_tag_cache(gb_set()) -> 'ok'.
   update_tag_cache(TagCache) ->
       gen_server:cast(?MODULE, {update_tag_cache, TagCache}).
  -
  --spec gc_blacklist([node()]) -> 'ok'.
  -gc_blacklist(Nodes) ->
  -    gen_server:cast(?MODULE, {gc_blacklist, Nodes}).
   
   %% ===================================================================
   %% gen_server callbacks
  
positive.code: gc_blacklist() ->
      gen_server:call(?MODULE, gc_blacklist).
  
  -spec choose_write_nodes(non_neg_integer(), [node()]) -> {'ok', [node()]}.
  choose_write_nodes(K, Exclude) ->
      gen_server:call(?MODULE, {choose_write_nodes, K, Exclude}).
  
negative.code: -export([get_tags/1,
           get_nodeinfo/1,
           get_read_nodes/0,
           get_hosted_tags/1,
           gc_blacklist/0,
           gc_blacklist/1,
           choose_write_nodes/2,
  