[erlang-questions] Out of memory and garbage collection

Christian chsu79@REDACTED
Thu Jan 22 14:02:11 CET 2009

Notice how gen_server allows init to return this form of tuple:

And handle_call has:{reply,Reply,NewState,hibernate}

And the other callbacks have similar forms as well.

2009/1/22 Jeroen Koops <koops.j@REDACTED>:
> Interesting, and consistent with what I'm seeing. I have an application that
> spawns a few thousand gen_servers. Each server instance initializes itself
> with a couple of mnesia queries, which may produce a lot of temporary data.
> The data that is eventually used as the gen_server's state is very limited,
> however.
> In my test-setup, after initialization, the gen_server's just sit idle, and
> indeed seem to hang on to all heap-memory needed during initialization,
> leading to an out-of-memory error after creating only a few hundred
> processes. This is solved by forcing a garbage collection right after
> initialization, and probably also by using the fullsweep_after spawn option
> (which I still have to look into).
> Thanks!
> On Thu, Jan 22, 2009 at 1:33 PM, Christian <chsu79@REDACTED> wrote:
>> 2009/1/22 Jeroen Koops <koops.j@REDACTED>:
>> > Hi,
>> >
>> > I have a simple question: In Java, it is guaranteed that, before an
>> > OutOfMemoryException it thrown, all possible garbage collection has been
>> > done. So, out of memory really means out of memory.
>> >
>> > Does a similar guarantee hold for Erlang as well? Or is it possible for
>> > the
>> > system to terminate with an out of memory error while garbage collection
>> > could have freed more memory?
>> The later. This article could probably be worth to read:
>>  http://www.lshift.net/blog/2008/10/31/erlangs-gc-only-runs-when-youre-running
>> This led to the strategy: "This sounds reasonable - let's try
>> hibernating after every message and see what happens." in this
>> article:
>>  http://www.metabrew.com/article/a-million-user-comet-application-with-mochiweb-part-2/
>> Garbage collection is per-process in the default memory model. As a
>> strategy, long running processes should probably do only little work
>> so they can be hibernated, and frequent work should probably be done
>> in short lived processes so all resources are freed instantly when
>> they die.
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