Erlang/OTP 17.1でmapsを使用する場合の注意点 ref: http://qiita.com/sile/items/48f1268d2e03915ca479

bench.erl

-module(bench).

-export([bench/0]).

-spec bench() -> [Result] when
      Result :: {module(), ElementSize::pos_integer(), InsertAverageNanoSeconds::non_neg_integer()}.
bench() ->
    ElementSizeList = [1, 10, 100, 1000, 10000, 100000], 
    InputList = [shuffle(lists:seq(0, Size - 1)) || Size <- ElementSizeList],

    ModuleList = [dict, gb_trees, maps],

    lists:sort(
      [do_bench(Module, Input) || Module <- ModuleList,
                                  Input <- InputList]).

-spec do_bench(module(), [non_neg_integer()]) -> Result when
      Result :: {module(), ElementSize::pos_integer(), InsertAverageNanoSeconds::non_neg_integer()}.
do_bench(Module, Input) ->
    ElementSize = length(Input),
    LoopCount = 100000 div ElementSize,  % 一回のベンチマーク中の挿入操作の回数を等しくさせるために、ループ数で調整する

    Empty = make_empty(Module),
    Fun   = get_insert_fun(Module),

    {TotalMicroSeconds, _} =
        timer:tc(fun () -> bench_loop(LoopCount, Empty, Fun, Input) end),
    AverageNanoSeconds = round((TotalMicroSeconds * 1000) / 100000),
    {Module, ElementSize, AverageNanoSeconds}.

-spec make_empty(module()) -> term().
make_empty(dict)     -> dict:new();
make_empty(gb_trees) -> gb_trees:empty();
make_empty(maps)     -> maps:new().

-spec get_insert_fun(module()) -> fun ((term(), term(), term()) -> term()).
get_insert_fun(dict)     -> fun dict:store/3;
get_insert_fun(gb_trees) -> fun gb_trees:enter/3;
get_insert_fun(maps)     -> fun maps:put/3.

-spec shuffle(list()) -> list().
shuffle(List) ->
    [X||{_,X} <- lists:keysort(1, [{random:uniform(), N} || N <- List])].

-spec bench_loop(non_neg_integer(), term(), function(), [non_neg_integer()]) -> ok.
bench_loop(0, _, _, _)                      -> ok;
bench_loop(LoopCount, Empty, Fun, Input) ->
    _ = lists:foldl(fun (N, Acc) -> Fun(N, N, Acc) end, Empty, Input),
    bench_loop(LoopCount - 1, Empty, Fun, Input).

erl_map.c

/* maps:get/2
 * return value if key *matches* a key in the map                                                                                                                                                                                                                                                                    
 * exception bad_key if none matches
 */

int erts_maps_get(Eterm key, Eterm map, Eterm *value) {
    Eterm *ks,*vs;
    map_t *mp;
    Uint n,i;

    mp  = (map_t*)map_val(map);
    n   = map_get_size(mp);

    if (n == 0)
        return 0;

    ks  = map_get_keys(mp);
    vs  = map_get_values(mp);

    if (is_immed(key)) {
        for( i = 0; i < n; i++) {
            if (ks[i] == key) {
                *value = vs[i];
                return 1;
            }
        }
    }

    for( i = 0; i < n; i++) {
        if (EQ(ks[i], key)) {
            *value = vs[i];
            return 1;
        }
    }
    return 0;
}