The result_set param is useful to obtain a result set quickly and
    easily. However, if the result set is going to be large, this comes with
    a cost in time and resources such as memory, since Virtuoso would have to
    obtain all results from the statement and build the result-set arrays in
    memory before returning.A more efficient way is to obtain a cursor handle and iterate
    through the result set one row at a time:To keep Virtuoso from obtaining the whole result set from the
    remote, pass NULL as the result_set parameter
    when calling rexecute.