From: John Joyce <dangerwillrobinsondanger@...>
Date: 2007-05-14T00:33:54+09:00
Subject: Re: DRb connection error with more than 250+ DRb services


On May 13, 2007, at 8:59 PM, Michal Suchanek wrote:

> On 13/05/07, Marcin Raczkowski <swistak@mailx.expro.pl> wrote:
>> On Friday 11 May 2007 08:25, J. Wook wrote:
>> > Simple test codes are here:
>> >
>> >
>> > class TestServer
>> >   include DRb::DRbUndumped
>> >
>> >   def initialize
>> >     @obj = Array.new
>> >   end
>> >
>> >   def register(addr)
>> >     @obj << addr
>> >   end
>> >
>> >   def sum
>> >     s = 0
>> >     @obj.each do |t|
>> >       v = DRbObject.new_with_uri(t).get_value
>> >       if v.nil?
>> >         puts s.to_s + " & error"
>> >       end
>> >       s += v
>> >     end
>> >     return s
>> >   end
>> > end
>> >
>> > class TestClient
>> >   include DRb::DRbUndumped
>> >
>> >   def initialize(addr, server, value)
>> >     DRbObject.new_with_uri(server).register(addr)
>> >     @value = value
>> >   end
>> >   def get_value
>> >     @value
>> >   end
>> > end
>> >
>> >
>> > uri = "druby://localhost:"
>> > server_uri = uri + "40000"
>> > server = DRb.start_service(server_uri, TestServer.new)
>> >
>> > max_size = 300
>> >
>> > (1..max_size).each do |t|
>> >   client_uri = uri + (40000 + t).to_s
>> >   DRb.start_service(client_uri, TestClient.new(client_uri,  
>> server_uri,
>> > t))
>> > end
>> >
>> > sum = DRbObject.new_with_uri(server_uri).sum
>> > puts sum
>> >
>> >
>> > For max_size = 10, sum = 55
>> > For max_size = 100, sum = 5050
>> >
>> > ...
>> >
>> > but
>> >
>> > For max_size = 300,
>> > DRb::DRbConnError exception raised.
>> >
>> > try to make another DRb server after that error in the same  
>> process....
>> > #<Errno::EMFILE: Too many open files - socket(2)> raised.
>> >
>> >
>> > How can I open more than 300 DRb connection?
>> > (I need to make about 1,000 connections .... )
>>
>> question probably everyone want's to ask.why the hell you need 1000
>> connections? dont' tell me you have 1000 servers with drbservers  
>> running
>> somewhere
>>
>
> It's been said that it's some 250 connections. For one, the
> application might act as some sort of proxy which would double the
> number of sockets.
>
> Apparently it either uses some other files of uses about 4
> handles/connection. It looks quite a lot and could be probably lowered
> but it does not change the fact that 1000 is a safe default for
> non-server applications but can be easily reached by servers.
>
> I wonder why such limits are imposed. It is probably some workaround
> for a flaw in UNIX design that introduces possible DoS by exhausting
> kernel memory/structures. Maybe it was fixed in some kernels (if
> that's even possible) but nobody cared to fix the limit as well.
>
> Thanks
>
> Michal
>
But aren't most socket-type connections really two file descriptors  
(coming and going)?
So the 250 would already be 500...?