[erlang-questions] Erlang Memory Question

[Robert Virding]

The obvious question is whether you are sure you actually need to optimise
to save memory? Premature optimisation and all that. (Actually sensible
advice) Maybe reviewing algorithms and datastructures will do the trick for
you.

Robert

>From my Nexus
 On Sep 24, 2014 7:37 PM, "Eranga Udesh" <eranga.erl@REDACTED> wrote:

> Thanks all for your advice. Let me see how I can apply them to my program.
> It looks like my code/logic is going to get ugly and induce a performance
> penalty, in order to save memory.
>
> Cheers,
> - Eranga
>
> On Wed, Sep 24, 2014 at 7:58 PM, Robert Raschke <rtrlists@REDACTED>
> wrote:
>
>> I always thought that is one of the reasons to have processes.
>> If you've got something big you want to throw away quickly, make a
>> process for it.
>>
>> $ erl
>> Erlang R16B03-1 (erts-5.10.4) [source] [64-bit] [smp:8:8]
>> [async-threads:10] [hipe] [kernel-poll:false]
>>
>> Eshell V5.10.4  (abort with ^G)
>> 1> erlang:memory().
>> [{total,14148416},
>>  {processes,4091608},
>>  {processes_used,4091488},
>>  {system,10056808},
>>  {atom,194289},
>>  {atom_used,172614},
>>  {binary,1514552},
>>  {code,4026600},
>>  {ets,262688}]
>> 2> Pid = spawn(
>> 2>   fun () ->
>> 2>     X = binary:copy(<<1,2,3,4,5,6,7,8>>, 1024),
>> 2>     Y = binary:copy(X, 1024),
>> 2>     receive stop -> ok end
>> 2>   end
>> 2> ).
>> <0.35.0>
>> 3> erlang:memory().
>> [{total,22643832},
>>  {processes,4203448},
>>  {processes_used,4203448},
>>  {system,18440384},
>>  {atom,194289},
>>  {atom_used,175110},
>>  {binary,9685320},
>>  {code,4221791},
>>  {ets,267056}]
>> 4> Pid ! stop.
>> stop
>> 5> erlang:memory().
>> [{total,13587776},
>>  {processes,4084496},
>>  {processes_used,4084384},
>>  {system,9503280},
>>  {atom,194289},
>>  {atom_used,175110},
>>  {binary,748144},
>>  {code,4221791},
>>  {ets,267056}]
>> 6>
>>
>>
>> Regards,
>> Robby
>>
>>
>> On 24 September 2014 02:13, Eranga Udesh <eranga.erl@REDACTED> wrote:
>>
>>> Well, yes I may deliberately lie.
>>>
>>> However my suggestion is to, instead of doing a full sweep by the
>>> garbage collector (GC) to identify data going out of scope and reclaim, can
>>> the program (or rather I) deliberately say I (the calling process) is
>>> finished using the said data, so the GC may free that part.
>>>
>>> Then the GC may carry out it's own logic, which it currently does to
>>> verify if the same data is referenced by any other processes, etc., and
>>> decide if to GC or not.
>>>
>>> = Eranga
>>>
>>> On Tue, Sep 23, 2014 at 12:42 PM, Richard A. O'Keefe <ok@REDACTED>
>>> wrote:
>>>
>>>>
>>>> On 23/09/2014, at 2:24 PM, Eranga Udesh wrote:
>>>>
>>>> > Thanks for the information received so far.
>>>> >
>>>> > Wouldn't it be good for Erlang to have a single object garbage
>>>> collection function/bif?
>>>>
>>>> NO.  In C it's called free() and it's a major cause of errors.
>>>>
>>>> > For example, when I no longer require a large object, I force to
>>>> garbage collect it, without making a full sweep?
>>>>
>>>> Why should the garbage collector *believe* you that the "object"
>>>> is free?  You could be deliberately lying.  You could (and
>>>> probably are) be mistaken.  How is it to know which bits you
>>>> want to keep without doing its usual thing?  In a shared heap
>>>> implementation (which Erlang has had and may have again) the
>>>> fact that *you've* finished with the object doesn't mean
>>>> everyone *else* has.  A meaningful operation should not depend
>>>> on implementation details like that.
>>>> >
>>>> > As mentioned in the document, a full sweep may degrade the
>>>> performance.
>>>>
>>>> Not half as much as freeing too much would!
>>>>
>>>> This is micro-optimisation.  Avoid passing around large
>>>> objects in the first place.
>>>>
>>>>
>>>
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>>>
>>>
>>
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