increase Number of filedescriptors

["Torsten Valentin" <winsock2@musiker.de>]

I'm about to use pen (http://siag.nu/pen) as a loadbalancer for a really
large number of ssl-connections that remain open for up to a few weeks
each. So there's about 10.000 simultaneous connections that need to be
handled. I compiled PEN and it works fine as far as I can see. The pen
docu says I can compile pen so that it is able to handle 20.000
connections, but there might be limitations by the OS. This is where my
question is aiming. 

What are those limitations, why are they, where are they, how can I
modify them? What disadvantages are there after modifying this to 20.000
?

After starting pen (on an OpenBSD3.0 machine with generic kernel) I saw
that conn_max (max number of simultaneous connections) is limited to 256
though I compiled pen for 20.000 simultaneous connections.

>From pen-manual: 
"--with-fd_setsize=N     set FD_SETSIZE to N

To use Pen with a very large number of simultaneous connections, the
preprocessing macro FD_SETSIZE must be increased. The default value
varies
between operating systems, as does the maximum supported. Pen will try
to
catch attempts to run out of spec."

Thanks in advance!

T.