[erlang-questions] simple question about list memory consumption

CGS <>
Fri Jul 6 14:54:24 CEST 2012


Thank you all for your time in answering. It seems my memory entered
holiday already. :)

Regards,
CGS





On Fri, Jul 6, 2012 at 2:38 PM, Magnus Henoch <
> wrote:

> Hm, ignore my previous answer, then; I was under the impression that
> small enough integers would be stored as immediates in the
> list cell...
>
> ----- Original Message -----
> >
> > http://www.erlang.org/doc/efficiency_guide/advanced.html
> >
> >
> > The data structure you want for space efficiency is binary.
> >
> > On Friday, July 6, 2012, CGS wrote:
> >
> >
> > Hi everyone,
> >
> >
> > I am puzzled by a behavior I didn't expect, so, if anyone can help to
> > understand it, I would appreciate.
> >
> >
> > Let's consider a string of latin1 characters. When dumped to a file
> > on a harddisk it occupies, as expected, 1 B per character. When
> > loaded in a variable in Erlang shell, I get about 21 B per character
> > (at least free is reporting that). Of course, it is hard to test on
> > one character due to changing RAM consumption of other processes.
> > So, my test case consisted in (I voided writing down and reading
> > from a file in the test case):
> > 1. stabilizing the environment (no other processes were started, but
> > the OS ones and watching for the RAM consumption stabilization at
> > the level of MB - give or take 1MB);
> > 2. opening an Erlang shell (few MB consumption - stable);
> > 3. executing:
> >
> >
> > L = lists:map(fun(_) -> 107 end,lists:seq(1,10000000)), ok.
> >
> >
> > where (I know it's obvious, but just for completeness):
> > - 107 is representing "k" character;
> > - the 'ok' atom at the end is for not writing the content of L in the
> > shell;
> > - the list [107,107,...] is equivalent to "kk..." string (which
> > written in a plain text file it gives 1 B per character as it is
> > expected).
> >
> >
> > The occupied RAM jumped by 214-217 MB for 10^7 characters (at 10^6
> > characters, I got 21 MB, so, it is related to the string length
> > only), which gives about 21 B per character (one can compute within
> > the errors the exact the size, but I took that value as the minimum
> > possible).
> >
> >
> > Erlang shell reports "Erlang R15B01 (erts-5.9.1) [source] [smp:4:4]
> > [async-threads:0] [hipe] [kernel-poll:false] [dtrace]".
> >
> >
> > I know that this isn't a big problem, but I am missing something here
> > for sure. Can anyone point what I am missing? Thank you in advance.
> >
> >
> > Regards,
> > CGS
> >
> >
> > _______________________________________________
> > erlang-questions mailing list
> > 
> > http://erlang.org/mailman/listinfo/erlang-questions
> >
>
> --
> Magnus Henoch
> Erlang Solutions Ltd
> http://www.erlang-solutions.com/
>
>
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