se the
         leader is not reading tuples fast enough, but requires the leader
         process to wait for worker processes to start up before the first
         tuples can be produced.  The degree to which the leader can help or
         hinder performance depends on the plan type, number of workers and
         query duration.
        </p></dd><dt id="GUC-OLD-SNAPSHOT-THRESHOLD"><span class="term"><code class="varname">old_snapshot_threshold</code> (<code class="type">integer</code>)
       <a id="id-