sysctl kern.ipc.somaxconn limit 65535 why?

Chuck Swiger cswiger at
Thu Jan 5 01:49:50 UTC 2012

Hi, Xin--

On Jan 4, 2012, at 5:32 PM, Xin Li wrote:
> I am personally quite convinced that FreeBSD should make such change
> though -- having more than 64K of outstanding and unhandled
> connections does not sound a great idea (i.e. it's not a connection
> limit after all, but the pending handle connection.  If my math were
> right, 64K connections would require about 1Gbps bandwidth in and out
> if they happen in the same second.)  But I agree this would be a good
> stress test, which might expose some bugs we don't know today.

I think I agree with the change from a correctness standpoint-- listen(2) accepts an int backlog argument.

I'm not convinced that there are many scenarios where needing to exceed a listen queue backlog of 64K would be beneficial to a real-world system, and I am sure there are many scenarios where it would be counterproductive, but folks can adjust kern.ipc.somaxconn as they see fit and perhaps Dan or others would gain some value from it.


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