magic wtf

qlct.erl

-module(qlct).
-compile([export_all]).

fill(T0, T1, []) -> {T0, T1};

fill(T0, T1, [H | T]) ->
  ets:insert(T0, {H, make_ref()}),
  ets:insert(T1, {H, make_ref()}),
  fill(T0, T1, T).

table(N) ->
  T0 = ets:new(ets, [ordered_set, private]),
  T1 = ets:new(ets, [set, private]),
  fill(T0, T1, lists:seq(0, N)).

i() ->
  [{N, M, i(N, M)} || N <- [50000, 100000, 200000, 500000, 1000000, 2000000, 5000000],
                      M <- [1000, 10000, 20000, 49000]].

i(N, M) ->
  {T0, T1} = table(N),
  {Time0, _} = timer:tc(?MODULE, ets_select2, [T0, T0, 0, [], M]),
  {Time1, _} = timer:tc(?MODULE, ets_select2, [T0, T1, 0, [], M]),
  [ets:delete(T) || T <- [T0, T1]],
  {Time0, Time1}.

ets_select2(_, _, _, Acc, 0) -> Acc;

ets_select2(T, T2, Key, Acc, N) ->
  [V] = ets:lookup(T2, Key),
  Key2 = ets:next(T, Key),
  ets_select2(T, T2, Key2, [V | Acc], N - 1).