sendfile returning ENOTCONN under heavy load

[Kevin Day]

I'm using thttpd on a server that pushes 300-400mbps of static content, 
using sendfile(2).

Once the load reaches a certain point (around 800-1000 clients 
downloading, anywhere from 150-250mbps), sendfile() will start randomly 
returning ENOTCONN, and the client is disconnected. I've raised 
kern.ipc.nsfbufs pretty high and that hasn't made any difference. Is 
there any easy way to tell exactly why the sockets are being closed? I 
can't seem to find any obvious signs of memory exhaustion or anything.

Thanks,

Kevin