[erlang-questions] Garbage collecting binaries

Nicholas Frechette <>
Thu Oct 7 16:57:19 CEST 2010


A bit hard to understand what is happening without seeing f(A)'s code.
AFAIK, even if you don't keep a reference to a binary, if you keep a
reference to a binary created from it, it'll keep it in full in memory.
ie:
A = << some large binary>>.
<<B:32/binary, _/binary>> = A.
If you keep no references to A but you do to B, A will remain in memory
because B will have been created as a pointer offset from A (as an
optimization).

Nicholas

On Thu, Oct 7, 2010 at 10:07 AM, tom kelly <> wrote:

> Hello List,
>
> I need some help on garbage collecting binaries.
> I have an application that handles large binaries and under load it eats up
> all the available memory then falls over, even when I start all the
> data-handling processes with "{spawn_opt,[{fullsweep_after, 20}]}".
>
> Reading point 5.15 on the page:
> http://www.erlang.org/faq/how_do_i.html
> leads me to think that calling the garbage collector on the process that
> created a binary will clean it up but my shell experiment below shows me
> I'm
> wrong. It's now 10 minutes since I've done this experiment and the large
> binary is still in memory.
>
> Maybe I have to call the garbage collector of the process whose heap is
> storing the binary? If so, which process is it?
>
> Any pointers as to what I'm doing wrong or mis-understand will be greatly
> appreciated.
>
> I'm on a legacy R12B5 system.
>
> //Tom.
>
>
>
> 18> process_info(self(),total_heap_size).
> {total_heap_size,4181}
>
> 19> A = L(100000).
> [140,161,41,128,44,96,215,43,15,164,88,107,1,167,4,125,118,
>  180,121,181,160,124,244,140,169,215,31,82,43|...]
>
> 20> process_info(self(),total_heap_size).
> {total_heap_size,1149851}
>
> 21> f(A).
> ok
>
> 22> erlang:garbage_collect().
> true
>
> 23> process_info(self(),total_heap_size).
> {total_heap_size,3194}
>
>
> 24> memory(binary).
> 6536
>
> 25> A = B(100000).
> <<232,241,55,171,218,35,86,122,211,185,232,1,203,249,181,
>  218,176,33,88,131,102,56,102,82,158,114,200,174,253,...>>
>
> 26> memory(binary).
> 106704
>
> 27> f(A).
> ok
>
> 28> memory(binary).
> 106704
>
> 29> erlang:garbage_collect().
> true
>
> 30> memory(binary).
> 106560
>


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