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分布式执行计划调度

分布式执行计划的简单调度模型如下:

在执行计划生成的最后阶段,以 EXCHANGE 节点为界,拆分成多个子计划,每个子计划被封装成为一个 DFO,在并行度大于 1 的场景下,会一次调度两个 DFO,依次完成 DFO 树的遍历执行;在并行度等于 1 的场景下,每个 DFO 会将产生的数据存入中间结果管理器,按照后序遍历的形式完成整个 DFO 树的遍历执行。

单 DFO 调度

示例:在并行度为 1 的场景下,对于查询计划执行单 DFO 调度。

======================================================================================
|ID|OPERATOR                             |NAME                 |EST. ROWS |COST      |
--------------------------------------------------------------------------------------
|0 |LIMIT                                |                     |10        |6956829987|
|1 | PX COORDINATOR MERGE SORT           |                     |10        |6956829985|
|2 |  EXCHANGE OUT DISTR                 |:EX10002             |10        |6956829976|
|3 |   LIMIT                             |                     |10        |6956829976|
|4 |    TOP-N SORT                       |                     |10        |6956829975|
|5 |     HASH GROUP BY                   |                     |454381562 |5815592885|
|6 |      HASH JOIN                      |                     |500918979 |5299414557|
|7 |       EXCHANGE IN DISTR             |                     |225943610 |2081426759|
|8 |        EXCHANGE OUT DISTR (PKEY)    |:EX10001             |225943610 |1958446695|
|9 |         MATERIAL                    |                     |225943610 |1958446695|
|10|          HASH JOIN                  |                     |225943610 |1480989849|
|11|           JOIN FILTER CREATE        |                     |30142669  |122441311 |
|12|            PX PARTITION ITERATOR    |                     |30142669  |122441311 |
|13|             TABLE SCAN              |CUSTOMER             |30142669  |122441311 |
|14|           EXCHANGE IN DISTR         |                     |731011898 |900388059 |
|15|            EXCHANGE OUT DISTR (PKEY)|:EX10000             |731011898 |614947815 |
|16|             JOIN FILTER USE         |                     |731011898 |614947815 |
|17|              PX BLOCK ITERATOR      |                     |731011898 |614947815 |
|18|               TABLE SCAN            |ORDERS               |731011898 |614947815 |
|19|       PX PARTITION ITERATOR         |                     |3243094528|1040696710|
|20|        TABLE SCAN                   |LINEITEM(I_L_Q06_001)|3243094528|1040696710|
======================================================================================

如下图所示,DFO 树除 ROOT DFO 外,在垂直方向上被分别划分为 0、1、2 号 DFO, 从而后序遍历调度的顺序为 0->1->2,即可完成整个计划树的迭代。

1

两 DFO 调度

示例:对于并行度大于 1 的计划, 对于查询计划执行两 DFO 调度。

Query Plan
=============================================================================
|ID|OPERATOR                                   |NAME    |EST. ROWS|COST     |
-----------------------------------------------------------------------------
|0 |PX COORDINATOR MERGE SORT                  |        |9873917  |692436562|
|1 | EXCHANGE OUT DISTR                        |:EX10002|9873917  |689632565|
|2 |  SORT                                     |        |9873917  |689632565|
|3 |   SUBPLAN SCAN                            |VIEW5   |9873917  |636493382|
|4 |    WINDOW FUNCTION                        |        |29621749 |629924873|
|5 |     HASH GROUP BY                         |        |29621749 |624266752|
|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       |
|12|            EXCHANGE IN DISTR              |        |1        |53       |
|13|             EXCHANGE OUT DISTR (BROADCAST)|:EX10000|1        |53       |
|14|              PX BLOCK ITERATOR            |        |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|
|21|         TABLE SCAN                        |PARTSUPP|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 号和 2 号 DFO,依次迭代完成执行。

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