presto-main/src/main/java/io/prestosql/execution/scheduler/AllAtOnceExecutionSchedule.java/AllAtOnceExecutionSchedule/processFragment
class AllAtOnceExecutionSchedule:        public void processFragment(PlanFragmentId planFragmentId)
        {
            PlanFragment planFragment = fragments.get(planFragmentId);
            checkArgument(planFragment != null, "Fragment not found: %s", planFragmentId);

            planFragment.getRoot().accept(this, null);
            schedulerOrder.add(planFragmentId);
        }