[erlang-questions] Increase the handle limit

[Peer Stritzinger]

On Fri, Oct 21, 2011 at 9:35 AM, Joel Reymont <joelr1@REDACTED> wrote:
> I don't think you can.
>
> I bump against this all the time on the Mac.
>
> Erlang uses the FD_SETSIZE setting from the system header files when compiled, normally 1024.

I took the time and wrote a little test because this sounded too
unbelievable, but nobody disagreed.

TL;DR Version: This is not true.  Tested on MacOSX 10.5.8 on PowerPC
with Erlang R14B03
(used the oldest version of Mac OSX anybody sane would run and the
Erlang is also not cutting edge version):

Could open about 56000 files the I hit some OS system limit.  Didn't
try to increase further since this already 50 times the amount of
FD_SETSIZE which is indeed set to 1024 on my system.

In order to be able to do this I had to do this:

Set ERL_MAX_PORTS (see erlang manpage) to increase the number of ports.

Set ulimit -n to allow more open files in the process

Start Erlang with +P to allow enough processes

With this settings I get up to about 10000 open files since I can't
set the ulimit above the system limit.  In order to get more I had to

      sysctl -w kern.maxfiles=120000
      sysctl -w kern.maxfilesperproc=100000

The increase ulimits -n and rerun the test:

    {enfile,56016}

Error enfile means from open(2):

    [ENFILE]           The system file table is full.

Since I set maxfiles to 120000 there should have been more files
possible, don't know what limit I hit, maybe number of files in a
directory?

Definitely not a Erlang limit though.

The program I used is below.
>
> Editing this value and re-compiling Erlang causes epmd to stop working.

This is no wonder.  Editing the header doesn't change the system call
internals, probably epmd uses select() which fails because the system
call  won't handle sets with increased set size.

Editing the system headers is definitely not to recommend.  It may
break all kinds of libraries in a subtle way.

> My solution is to save the old epmd and recompile after editing the system header files.
>
> On Oct 21, 2011, at 7:25 AM, Martin Dimitrov wrote:
>
>> Hi all,
>>
>> I am developing on a Windows 7 machine, Erlang R14B04. The limit of open
>> handles seems to be 1200. But this is not imposed by the operating
>> system (Windows has a hard coded limit of 16 million handles). So my
>> question is how can I increase the handle limit in Erlang?

All this probably won't help you solving the Windows problem in a
systematic way, unfortunately (actually fortunately I think ;-) I'm no
Windows expert.

Looking the the corresponding source files of ERTS might help:

* find out how Erlang finds out about file descriptor changes

* find out where the limit comes from

Also what might lead you to the reason of the limit is the exact error
message you get when you hit the limit.

Cheers
-- Peer

Little program used to find limit and reason:

-module(test_fds).
-compile([export_all]).

count() ->
    count(1, []).

count(N, Fds) ->
    case file:open(integer_to_list(N), [write]) of
	{ok, F} ->
	    count(N+1, [F| Fds]);
	{error, Err} ->
	    [ file:close(F) || F <- Fds ],
	    {Err, N}
    end.


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