remote exchange (GATHER, SINGLE, [])
    local exchange (GATHER, UNKNOWN, [])
        remote exchange (REPARTITION, ROUND_ROBIN, [])
            final aggregation over (linestatus, returnflag)
                local exchange (GATHER, SINGLE, [])
                    remote exchange (REPARTITION, HASH, ["linestatus", "returnflag"])
                        partial aggregation over (linestatus, returnflag)
                            scan lineitem
