ab测试中的Erlang/牛仔崩溃(套接字重置)

正在试用Cowboy（Erlang）http库，helloworld示例：https://github.com/extend/cowboy/tree/master/examples/hello_world

当以这种方式使用Apache的"ab"测试工具时，我会得到"连接重置"：

d7 ~/cb/cowboy/examples/hello_world % !564
ab -n 30000 -c 5000 http://127.0.0.1:8080/
This is ApacheBench, Version 2.3 <$Revision: 655654 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/
Benchmarking 127.0.0.1 (be patient)
Completed 3000 requests
Completed 6000 requests
Completed 9000 requests
Completed 12000 requests
Completed 15000 requests
Completed 18000 requests
Completed 21000 requests
Completed 24000 requests
Completed 27000 requests
apr_socket_recv: Connection reset by peer (104)

使用较小值（如-n 5000-c 1000）进行测试可以正常工作。

崩溃或重置erl/Cowboy流程的问题可能是什么？我观察到beam的内存使用率在顶部，它增长到了像120MB这样的smth，没有什么淫秽的（我在那个vm上有3G的RAM）。

ulimit设置也相当慷慨：

% ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 24088
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 65535
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 16000
cpu time               (seconds, -t) unlimited
max user processes              (-u) 24088
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

erl/牛仔可能有什么问题？

操作系统：Debian 7 x64。