presto-main/src/main/java/io/prestosql/execution/scheduler/PhasedExecutionSchedule.java/PhasedExecutionSchedule/visitSemiJoin
class PhasedExecutionSchedule:        @Override
        public Set<PlanFragmentId> visitSemiJoin(SemiJoinNode node, PlanFragmentId currentFragmentId)
        {
            return processJoin(node.getFilteringSource(), node.getSource(), currentFragmentId);
        }