[JDEV] Stress testing and connection limits

Thomas Charron tcharron at ductape.net
Wed Jun 14 14:46:33 CDT 2000

Quoting Chuck Bohling <chuck at ultris.com>:
> ulimit on my Linux server that jserver is running on reports 1024 open file
> handles. I've tried changing that number with ulimit but I'm not sure if
> the
> number of handles really changes. I don't think so. The implication from
> what you've said is that the max number of jabber users connected at one
> point is limited. In my case, 1024. Is that true? Isn't that as fairly
> serious restriction? I was expecting to have a powerful server with 10's
> maybe 100's of thousands of connected users. Can the kernel be rebuilt with
> a larger size? If I change the limit to 100,000 or 200,000, will Linux
> still
> run?

  Yes, it will still run fine.  The kernel, however, will consume a large 
amount of memory in simply managing that many IP sockets at the same time.  I 
cannot say exactly how much, but there is overhead.  A safer number would be 
like 32,000.

  To address this situation, two things can be done.  One is *ALREADY* being 
worked on by the team, in the usage of a connection multiplexor of sorts, which 
would basically allow several low end machines accepting connections in front 
of a larger 'processing' machine, almost like a Web Server <-> application 
server environment.  The second option would be to modify the servers to allow 
UDP communications.  This would introduce overhead in and of itself, and a 
lower level protocol would be required simply do to the fact that delivery 
information, etc, would now have to be handled at the application level, 
instead of by the OS.  For background data, UDP is a connectionless protocol, 
so using it in a connected environment requires a subprotocol to be used to 
perform the virtual 'connection'.  The svc_http actually does something 
simular, but in an HTTP connectionless environment.  It does NOT handle 
gaurunteed delivery, which is something that would also need to be in a UDP 
based service.

Thomas Charron
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