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  • Subject: Re: Altering the SOMAXCONN value.
  • From: John Dorn <jdorn@xxxxxxxxxx>
  • Date: Wed, 22 Oct 1997 09:36:06 -0400
  • Organization: I/NET, Inc.

In our server products we default the connection queue size to 64 and
allow our customers to change this value if it is not appropriate.  I
have never seen any (AS/400) documentation that indicates the optimal
setting, or if a large value effects the system/processing in a
negative way.  The size of the queue depends on the maximum concurrent
requests the server can expect, the system performance and how quickly
the server can turn around to grab the next request using accept().

FYI: For non-threaded programs, the socket functions givedescriptor()
and takedescriptor() can be used to transfer socket descriptors between
jobs on the AS/400.  Also, the CPA (Common Programming APIs) OS/400
option is free, just needs to be installed (asked in another response).
Many ported UNIX applications require this option to be installed.

Hope the helps,

John Dorn
I/NET, Inc.

Walden Leverich wrote:
> 
> Why would you want to? Usually you have one thread listen for connections,
> pass the connection off to another thread for processing, and then go back
> to listening for connections. The SOMAXCONN should be large enough to
> handle the backlog that will occur while you spawn a thread, so 5 is
> usually sufficient and 512 should be more than enough.
> 
> However, now that I am thinking about this, the 400 does not support
> threads, so I'm not sure how you would handle this on the 400. I doubt you
> can pass connection handles between jobs, but maybe you can. How are you
> processing the connections? Anyway, if you have more than 512 clients
> waiting on the server to listen() for them you may have a problem.
> 
> -Walden
> 
> -----Original Message-----
> From:   Ed.Doxtator@ssa.co.uk [SMTP:Ed.Doxtator@ssa.co.uk]
> Sent:   Monday, October 20, 1997 11:35 AM
> To:     MIDRANGE-L@midrange.com
> Subject:        Altering the SOMAXCONN value.
> 
> Hey All!
> 
> We're in the middle of doing some TCP/IP stress-testing, and in the course
> of our research, we've found that when you do a listen(), there's two
> parameters allowed.  The first is the socket you're going to listen on.
> The second is the maximum number of connections TCP/IP will backlog before
> connection requests to that socket are rejected.
> 
> The usual limit for Unix systems appears to be something like 5.  The
> AS/400 has a maximum number allowed, defined in QSYSINC/SYS(SOCKET) called
> SOMAXCONN.  The limit is 512.
> 
> Has anyone changed this limit to something higher?  If so, what happened?
> 
> Look after yerselves...
> 
> Thanks,
> 
> -Doc
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