liyunzhang_intel commented on HIVE-16600:

[~lirui]: one thing you proposed in review board
bq.Does multi insert always branch at SEL like this? Please try more cases to 
I think it is yes, [~xuefuz]: can you give us you option about this? multi 
insert case
  // TS[0]-SEL[1]-RS[2]-SEL[3]-SEL[4]-FS[5]

there is definitely a SEL(SEL[3]) after RS( multi -insert RS , here RS[2]), if 
the children size of SEL(SEL[3]) is more than 1, this is how we judge a 
multi-insert case?

> Refactor SetSparkReducerParallelism#needSetParallelism to enable parallel 
> order by in multi_insert cases
> --------------------------------------------------------------------------------------------------------
>                 Key: HIVE-16600
>                 URL: https://issues.apache.org/jira/browse/HIVE-16600
>             Project: Hive
>          Issue Type: Sub-task
>            Reporter: liyunzhang_intel
>            Assignee: liyunzhang_intel
>         Attachments: HIVE-16600.1.patch, HIVE-16600.2.patch, 
> HIVE-16600.3.patch, HIVE-16600.4.patch, HIVE-16600.5.patch, 
> HIVE-16600.6.patch, HIVE-16600.7.patch, mr.explain, mr.explain.log.HIVE-16600
> multi_insert_gby.case.q
> {code}
> set hive.exec.reducers.bytes.per.reducer=256;
> set hive.optimize.sampling.orderby=true;
> drop table if exists e1;
> drop table if exists e2;
> create table e1 (key string, value string);
> create table e2 (key string);
> FROM (select key, cast(key as double) as keyD, value from src order by key) a
>     SELECT key, value
>     SELECT key;
> select * from e1;
> select * from e2;
> {code} 
> the parallelism of Sort is 1 even we enable parallel order 
> by("hive.optimize.sampling.orderby" is set as "true").  This is not 
> reasonable because the parallelism  should be calcuated by  
> [Utilities.estimateReducers|https://github.com/apache/hive/blob/master/ql/src/java/org/apache/hadoop/hive/ql/optimizer/spark/SetSparkReducerParallelism.java#L170]
> this is because SetSparkReducerParallelism#needSetParallelism returns false 
> when [children size of 
> RS|https://github.com/apache/hive/blob/master/ql/src/java/org/apache/hadoop/hive/ql/optimizer/spark/SetSparkReducerParallelism.java#L207]
>  is greater than 1.
> in this case, the children size of {{RS[2]}} is two.
> the logical plan of the case
> {code}
>    TS[0]-SEL[1]-RS[2]-SEL[3]-SEL[4]-FS[5]
>                             -SEL[6]-FS[7]
> {code}

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