he default value is 2.  Setting this value to 0
         disables parallel query execution.
        </p><p>
         Note that parallel queries may consume very substantially more
         resources than non-parallel queries, because each worker process is
         a completely separate process which has roughly the same impact on the
         system as an additional user session.  This should be taken into
         account when choosing a value for this setting, as well as when
         configuring other s