presto-main/src/main/java/io/prestosql/sql/planner/PlanFragmenter.java/FragmentProperties/setCoordinatorOnlyDistribution
class FragmentProperties:        public FragmentProperties setCoordinatorOnlyDistribution()
        {
            if (partitioningHandle.isPresent() && partitioningHandle.get().isCoordinatorOnly()) {
                // already single node distribution
                return this;
            }

            // only system SINGLE can be upgraded to COORDINATOR_ONLY
            checkState(!partitioningHandle.isPresent() || partitioningHandle.get().equals(SINGLE_DISTRIBUTION),
                    "Cannot overwrite partitioning with %s (currently set to %s)",
                    COORDINATOR_DISTRIBUTION,
                    partitioningHandle);

            partitioningHandle = Optional.of(COORDINATOR_DISTRIBUTION);

            return this;
        }