Erlang's maximum number of simultaneous open ports?

Question

Does the erlang TCP/IP library have some limitations? I've done some searching but can't find any definitive answers.

I have set the ERL_MAX_PORTS environment variable to 12000 and configured Yaws to use unlimited connections.

I've written a simple client application that connects to an appmod I've written for Yaws and am testing the number of simultaneous connections by launch X number of clients all at the same time.

I find that when I get to about 100 clients, the Yaws server stops accepting more TCP connections and the client errors out with

Error in process  with exit value: {{badmatch,{error,socket_closed_remotely}}

I know there must be a limit to the number of open simultaneous connections, but 100 seems really low. I've looked through all the yaws documentation and have removed any limit on connections.

This is on a 2.16Ghz Intel Core 2 Duo iMac running Snow Leopard.

A quick test on a Vista Machine shows that I get the same problems at about 300 connections.

Is my test unreasonable? I.e. is it silly to open 100+ connections simultaneously to test Yaws' concurrency?

Thanks.

Answer 1

It seems you hit a system limitation, try to increase the max number of open files using

$ ulimit -n 500

Python on Snow Leopard, how to open >255 sockets?

Erlang itself has a limit of 1024:

From http://www.erlang.org/doc/man/erlang.html

The maximum number of ports that can be open at the same time is 1024 by default, but can be configured by the environment variable ERL_MAX_PORTS.

EDIT:

The system call listen() has a parameter backlog which determines how many requests can be queued, please check whether a delay between requests to establish connections helps. This could be your problem.