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分布式執(zhí)行計(jì)劃的簡(jiǎn)單調(diào)度模型如下：
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在執(zhí)行計(jì)劃生成的最后階段，以 EXCHANGE 節(jié)點(diǎn)為界，拆分成多個(gè)子計(jì)劃，每個(gè)子計(jì)劃被封裝成為一個(gè) DFO，在并行度大于 1 的場(chǎng)景下，會(huì)一次調(diào)度兩個(gè) DFO，依次完成 DFO 樹(shù)的遍歷執(zhí)行；在并行度等于 1 的場(chǎng)景下，每個(gè) DFO 會(huì)將產(chǎn)生的數(shù)據(jù)存入中間結(jié)果管理器，按照后序遍歷的形式完成整個(gè) DFO 樹(shù)的遍歷執(zhí)行。
單 DFO 調(diào)度
示例：在并行度為 1 的場(chǎng)景下，對(duì)于查詢計(jì)劃執(zhí)行單 DFO 調(diào)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|
======================================================================================如下圖所示，DFO 樹(shù)除 ROOT DFO 外，在垂直方向上被分別劃分為 0、1、2 號(hào) DFO, 從而后序遍歷調(diào)度的順序?yàn)?0->1->2，即可完成整個(gè)計(jì)劃樹(shù)的迭代。
兩 DFO 調(diào)度
示例：對(duì)于并行度大于 1 的計(jì)劃, 對(duì)于查詢計(jì)劃執(zhí)行兩 DFO 調(diào)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|
=============================================================================如下圖所示，DFO 樹(shù)除 ROOT DFO 外，被劃分為 3 個(gè) DFO，調(diào)度時(shí)會(huì)先調(diào) 0 和 1 對(duì)應(yīng)的 DFO，待 0 號(hào) DFO 執(zhí)行完畢后，會(huì)再調(diào)度 1 號(hào)和 2 號(hào) DFO，依次迭代完成執(zhí)行。
本文名稱：創(chuàng)新互聯(lián)OceanBase教程：OceanBase分布式執(zhí)行計(jì)劃調(diào)度
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