presto-main/src/main/java/io/prestosql/sql/planner/plan/ExchangeNode.java/ExchangeNode/gatheringExchange
class ExchangeNode:    public static ExchangeNode gatheringExchange(PlanNodeId id, Scope scope, PlanNode child)
    {
        return new ExchangeNode(
                id,
                ExchangeNode.Type.GATHER,
                scope,
                new PartitioningScheme(Partitioning.create(SINGLE_DISTRIBUTION, ImmutableList.of()), child.getOutputSymbols()),
                ImmutableList.of(child),
                ImmutableList.of(child.getOutputSymbols()),
                Optional.empty());
    }