在并行度为 1 的场景下, 对于如下查询计划执行单 DFO 调度。

两 DFO 调度示例

=============================================================================
|ID|OPERATOR                                   |NAME    |EST. ROWS|COST     |
-----------------------------------------------------------------------------
|0 |PX COORDINATOR MERGE SORT                  |        |9873917  |692436562|
|1 | EXCHANGE OUT DISTR                        |:EX10002|9873917  |689632565|
|2 |  SORT                                     |        |9873917  |689632565|
|4 |    WINDOW FUNCTION                        |        |29621749 |629924873|
|6 |      HASH JOIN                            |        |31521003 |591048941|
|7 |       JOIN FILTER CREATE                  |        |407573   |7476793  |
|8 |        EXCHANGE IN DISTR                  |        |407573   |7476793  |
|9 |         EXCHANGE OUT DISTR (BROADCAST)    |:EX10001|407573   |7303180  |
|10|          HASH JOIN                        |        |407573   |7303180  |
|11|           JOIN FILTER CREATE              |        |1        |53       |
|13|             EXCHANGE OUT DISTR (BROADCAST)|:EX10000|1        |53       |
|15|               TABLE SCAN                  |NATION  |1        |53       |
|16|           JOIN FILTER USE                 |        |10189312 |3417602  |
|17|            PX BLOCK ITERATOR              |        |10189312 |3417602  |
|18|             TABLE SCAN                    |SUPPLIER|10189312 |3417602  |
|19|       JOIN FILTER USE                     |        |803481600|276540086|
|20|        PX PARTITION ITERATOR              |        |803481600|276540086|
=============================================================================

如下图所示，DFO 树除 ROOT DFO 外, 被划分为 3 个 DFO, 调度时会先调 0 和 1 对应的 DFO, 待 0 号 DFO 执行完毕后, 会再调度 1 和 2 号 DFO, 依次迭代完成执行。