Increase default sockets for zmq gc. Avoids scaling issues.
    https://github.com/zeromq/pyzmq/issues/471

def _increase_gc_sockets():
    """Increase default sockets for zmq gc. Avoids scaling issues.
    https://github.com/zeromq/pyzmq/issues/471
    """
    ctx = zmq.Context()
    ctx.max_sockets = MAX_SOCKETS
    gc.context = ctx