Question

有人可以帮我理解如何为以下查询创建mapper和reducer。下面提到的是查询的查询和结果。我想知道：

为什么它有Map1和Map4，为什么不是Map2和Map3
为什么减少2,3而不是

有没有办法改善查询的性能？

hive>
        > select agegroup , sum(safe_cnt),sum(unsafe_cnt) from
        > (
        > select case when b.age <= 25 then 'age25' when (b.age > 25 and b.age < 35) then 'age35'
        > when (b.age >= 35 and b.age < 45) then 'age45' else 'age50' end as agegroup ,
        >  a.safe_cnt, a.unsafe_cnt  from
        > (select cust_id, sum (case when place = 'safe' then 1 else 0 end) as safe_cnt, sum (case when place = 'unsafe' then 1 else 0 end) as unsafe_cnt from               directive_ana.sensor_main group by cust_id) a
        > left outer join directive_ana.cust_main b where a.cust_id = b.cust_id
        > ) e
        > group by agegroup ;
    Query ID = root_xxxxx_xxxxxXxxx_xxx_xxx_xxx
    Total jobs = 1
    Launching Job 1 out of 1

状态：正在运行（在App ID为application_147071xxxxx_xxx的YARN群集上执行）

--------------------------------------------------------------------------------
VERTICES      STATUS  TOTAL  COMPLETED  RUNNING  PENDING  FAILED  KILLED
--------------------------------------------------------------------------------
Map 1 ..........   SUCCEEDED      1          1        0        0       0       0
Map 4 ..........   SUCCEEDED      1          1        0        0       0       0
Reducer 2 ......   SUCCEEDED      1          1        0        0       0       0
Reducer 3 ......   SUCCEEDED      1          1        0        0       0       0
--------------------------------------------------------------------------------
VERTICES: 04/04  [==========================>>] 100%  ELAPSED TIME: 9.17 s
--------------------------------------------------------------------------------
OK
age25   8       7
age35   202     166
age45   194     163
age50   740     611
Time taken: 14.04 seconds, Fetched: 4 row(s)

无法理解hive查询的Mapper和reducer

0 个答案: