presto-main/src/main/java/io/prestosql/operator/aggregation/TypedKeyValueHeap.java/TypedKeyValueHeap/getSerializedType
class TypedKeyValueHeap:    public static Type getSerializedType(Type keyType, Type valueType)
    {
        return RowType.anonymous(ImmutableList.of(BIGINT, new ArrayType(keyType), new ArrayType(valueType)));
    }