[erlang-questions] Performance of maps:get()

[Lukas Larsson]

Hello,

You do not ever want to run benchmarking in the shell. The code in the
shell and .beam files are very different and the performance differs
wildly. Compile your tests into a module and try again to see if you get
better results. When I do it I get {0,0} as the result.

Lukas

On Wed, May 18, 2016 at 5:35 AM, Avinash Dhumane <nistrigunya@REDACTED>
wrote:

> For my algorithm trading application, gains even in 5 to 10 microseconds
> matter.
>
> I used maps extensively to improve expressiveness of the design.
>
> But, here is a small observation about maps. I am not sure if the
> performance variation seen is indeed true, or if my test case is wrong. In
> either case, please point me to the right way of efficiently using of maps.
>
> avinash@REDACTED:~/tws$ erl
> Erlang/OTP 18 [erts-7.3] [source] [64-bit] [smp:2:2] [async-threads:10]
> [hipe] [kernel-poll:false]
>
> Eshell V7.3  (abort with ^G)
>
> %%% compute average of timer:tc() return values (timings)
>
> 1> Avg = fun(PerfList) -> Sum = lists:sum(lists:map(fun({Time, _}) -> Time
> end, PerfList)), Len = erlang:length(PerfList), Sum div Len  end.
> #Fun<erl_eval.6.50752066>
>
> %%% a test map of size 3
>
> 2> Map = #{{a, 1} => 100, {a, 2} => 200, {a, 3} => 300}.
> #{{a,1} => 100,{a,2} => 200,{a,3} => 300}
>
> %%% performance: without maps:get()
>
> 3> PerfList1 = lists:map(fun(_) -> timer:tc(fun() -> K1 = {a, 1}, K2 = {a,
> 2}, K3 = {a, 3}, #{K1 := V1, K2 := V2, K3 := V3} = Map, {V1, V2, V3} end)
> end, lists:seq(1,100)).
> [{111,{100,200,300}},
>  {81,{100,200,300}},
>  {88,{100,200,300}},
> .....details deleted.....
>  {91,{100,200,...}},
>  {83,{100,...}},
>  {85,{...}},
>  {107,...},
>  {...}|...]
>
> %%% performance: with maps:get()
>
> 4> PerfList2 = lists:map(fun(_) -> timer:tc(fun() -> {maps:get({a,1},
> Map), maps:get({a,2}, Map), maps:get({a,3}, Map)} end) end, lists:seq(1,
> 100)).
> [{13,{100,200,300}},
>  {12,{100,200,300}},
>  {33,{100,200,300}},
> .....details deleted.....
>  {13,{100,200,...}},
>  {12,{100,...}},
>  {12,{...}},
>  {12,...},
>  {...}|...]
>
> %%% compare performance: maps:get() is 7-times faster
>
> 5> {Avg(PerfList1), Avg(PerfList2)}.
> {89,13}
> 6>
>
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>
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