otp-22: performance degradation

[John Högberg]

Hi!

Thanks for pointing this out. As far as I can tell it doesn't have anything to do with dict, but is caused by lists:mapfoldl/3 using much more stack space than in OTP 21. We'll try to have this fixed before OTP 23.0-rc3.

/John

-----Original Message-----
From: erlang-questions <erlang-questions-bounces@REDACTED> On Behalf Of Alexey Antipov
Sent: Tuesday, March 31, 2020 11:08
To: erlang-questions@REDACTED
Subject: otp-22: performance degradation

Hi,

I  noticed that using of dict in some cases is significantly degraded in otp-22 comparing with otp-21.

Code:

~~~~~
#!/usr/bin/env escript

-mode(compile).

main([]) ->
  {Time,_} = timer:tc(fun() ->
                          %% lists:foldl has no degradation
                          lists:mapfoldl(fun(K,Dict) -> {1,dict:store(K,1,Dict)} end,
                                         dict:new(),
                                         lists:seq(1, 166666))
                      end),
  io:format("Time: ~b~n", [Time]),
  ok.
~~~~~

21.3.8.3: Time: 615437
22.3: Time: 5405957
23.0-rc2: Time: 5569684

Is this a known issue?
Should I create an issue at bugs.erlang.org?

Thanks