hadoop - 如何确定执行配置单元查询所需的作业总数

Question

有没有办法确定执行查询所需的作业总数。

例如，在下面的 2 个查询中，连接和子查询的数量相同，但一个查询需要 2 个作业，而其他查询需要 3 个

 select t1.item_dim_key hive, t2.item_dim_key as monet 
   from ext_dist_it_dim_key t1 
        left outer join (select distinct item_dim_key from PO_ITEM_DIM) t2 on t1.item_dim_key=t2.item_dim_key 
   where t2.item_dim_key is null;

WARNING: Hive-on-MR is deprecated in Hive 2 and may not be available in the future versions. Consider using a different execution engine (i.e. spark, tez) or using Hive 1.X releases.
Query ID = 20190208020329_258ee4c0-5819-4842-b479-d549c82a0779
**Total jobs = 3**

hive> select t1.item_dim_key hive, t2.item_dim_key as monet 
       from (select distinct item_dim_key from PO_ITEM_DIM) t1 
            left outer join ext_dist_it_dim_key t2 on t1.item_dim_key=t2.item_dim_key 
      where t2.item_dim_key is null;

WARNING: Hive-on-MR is deprecated in Hive 2 and may not be available in the future versions. Consider using a different execution engine (i.e. spark, tez) or using Hive 1.X releases.
Query ID = 20190208020624_9ea3dc20-ffc8-4461-9516-7a4770d1dd6b
**Total jobs = 2**

是否有可能知道执行一个查询需要多少个作业？计算作业数量所需的参数是什么。

谢谢

Answer 1

使用EXPLAIN , 它显示了查询执行计划。只有计划才能确定地回答这个问题。根据统计数据或表(文件)大小，优化器可以将一些连接转换为映射连接等。