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%%%
%%% Copyright 2012, Basho Technologies, Inc. All Rights Reserved.
%%%
%%% Licensed under the Apache License, Version 2.0 (the "License");
%%% you may not use this file except in compliance with the License.
%%% You may obtain a copy of the License at
%%%
%%% http://www.apache.org/licenses/LICENSE-2.0
%%%
%%% Unless required by applicable law or agreed to in writing, software
%%% distributed under the License is distributed on an "AS IS" BASIS,
%%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
%%% See the License for the specific language governing permissions and
%%% limitations under the License.
%%%
%%%-------------------------------------------------------------------
%%% File: folsom_sample_slide.erl
%%% @author Russell Brown <russelldb@basho.com>
%%% @doc
%%% Sliding window sample. Last Window seconds readings are recorded.
%%% @end
%%%-----------------------------------------------------------------
-module(folsom_sample_slide_uniform).
-export([
new/1,
update/2,
get_values/1,
moment/0,
trim/2,
resize/2
]).
-include("folsom.hrl").
new({Window, SampleSize}) ->
Sample = #slide_uniform{window = Window, size = SampleSize},
Pid = folsom_sample_slide_sup:start_slide_server(?MODULE, Sample#slide_uniform.reservoir, Sample#slide_uniform.window),
Sample#slide_uniform{server=Pid}.
update(#slide_uniform{reservoir = Reservoir, size = Size} = Sample0, Value) ->
Now = folsom_utils:timestamp(),
Moment = folsom_utils:now_epoch(Now),
MCnt = folsom_utils:update_counter(Reservoir, Moment, 1),
Sample = case MCnt > Size of
true ->
{Rnd, _NewSeed} = random:uniform_s(MCnt, Now),
maybe_update(Reservoir, {{Moment, Rnd}, Value}, Size),
Sample0;
false ->
ets:insert(Reservoir, {{Moment, MCnt}, Value}),
Sample0
end,
Sample.
resize(Sample, NewSize) ->
folsom_sample_slide_server:resize(Sample#slide.server, NewSize),
Sample#slide{window = NewSize}.
maybe_update(Reservoir, {{_Moment, Rnd}, _Value}=Obj, Size) when Rnd =< Size ->
ets:insert(Reservoir, Obj);
maybe_update(_Reservoir, _Obj, _Size) ->
ok.
get_values(#slide_uniform{window = Window, reservoir = Reservoir}) ->
Oldest = moment() - Window,
ets:select(Reservoir, [{{{'$1', '_'},'$2'},[{'>=', '$1', Oldest}],['$2']}]).
moment() ->
folsom_utils:now_epoch().
trim(Reservoir, Window) ->
Oldest = moment() - Window,
ets:select_delete(Reservoir, [{{{'$1', '_'},'_'},[{'<', '$1', Oldest}],['true']}]),
%% and trim the counters
ets:select_delete(Reservoir, [{{'$1','_'},[{is_integer, '$1'}, {'<', '$1', Oldest}],['true']}]).