Apache2::RequestIO sendfile

If I use $r->sendfile($filenam) and the file is always the same then
does mod_perl open and read this file on every execution or is it
cached? I am wondering if it will be better to copy the contents of
file (500bytes) in the perl module instead.

Is there a overhead or chances of running out of file handles if we
use sendfile? Or is there a better way of using senfile that will
ensure minimal overhead?