[erlang-questions] Understanding memory usage

Erik Søe Sørensen <>
Mon Jan 28 09:46:17 CET 2013


2013/1/26 Ward Bekker (TTY) <>

> Hi,
>
> I run into high memory usage (>1.5GB) when running `crack_util:crack` from
> this module: https://gist.github.com/4642789 (make sure crypto is
> running: `crypto:start()`). As far as I can see, it's not creating (or
> holding on to)  huge pieces of data.
>
> Why is that?
>

It happens in this line:
lists:seq(0, Products-1)).
because
Products = round(math:pow(length(?CHAR_LIST), TryLength)) = 59^5 = 714924299
lists:seq() is, as anything else in Erlang, calculated eagerly, so you get
a full representation of the list.
In a 32-bit Erlang VM, that takes 5,7GB.

You may want to write a function that folds over a range of integers, and
use that instead of lists:foldl(_,_,lists:seq(A,B)) :-)

/Erik
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