Github user jeanlyn commented on the pull request:
https://github.com/apache/spark/pull/6682#issuecomment-109871137
@yhuai .Yes,the full outer join cases shuffled the null key to the same
reducer in spark-sql ,and the hive plan generated like:
```sql
explain select a.value,b.value,c.value,d.value from
a full outer join b
on a.key = b.key
full outer join c
on a.key = c.key
full outer join d
on a.key = d.key
STAGE PLANS:
Stage: Stage-1
Map Reduce
Map Operator Tree:
TableScan
alias: a
Statistics: Num rows: 0 Data size: 0 Basic stats: NONE Column
stats: NONE
Reduce Output Operator
key expressions: key (type: string)
sort order: +
Map-reduce partition columns: key (type: string)
Statistics: Num rows: 0 Data size: 0 Basic stats: NONE Column
stats: NONE
value expressions: value (type: string)
TableScan
alias: b
Statistics: Num rows: 0 Data size: 0 Basic stats: NONE Column
stats: NONE
Reduce Output Operator
key expressions: key (type: string)
sort order: +
Map-reduce partition columns: key (type: string)
Statistics: Num rows: 0 Data size: 0 Basic stats: NONE Column
stats: NONE
value expressions: value (type: string)
TableScan
alias: c
Statistics: Num rows: 0 Data size: 0 Basic stats: NONE Column
stats: NONE
Reduce Output Operator
key expressions: key (type: string)
sort order: +
Map-reduce partition columns: key (type: string)
Statistics: Num rows: 0 Data size: 0 Basic stats: NONE Column
stats: NONE
value expressions: value (type: string)
TableScan
alias: d
Statistics: Num rows: 0 Data size: 0 Basic stats: NONE Column
stats: NONE
Reduce Output Operator
key expressions: key (type: string)
sort order: +
Map-reduce partition columns: key (type: string)
Statistics: Num rows: 0 Data size: 0 Basic stats: NONE Column
stats: NONE
value expressions: value (type: string)
Reduce Operator Tree:
Join Operator
condition map:
Outer Join 0 to 1
Outer Join 0 to 2
Outer Join 0 to 3
keys:
0 key (type: string)
1 key (type: string)
2 key (type: string)
3 key (type: string)
outputColumnNames: _col1, _col6, _col11, _col16
Statistics: Num rows: 0 Data size: 0 Basic stats: NONE Column
stats: NONE
Select Operator
expressions: _col1 (type: string), _col6 (type: string), _col11
(type: string), _col16 (type: string)
outputColumnNames: _col0, _col1, _col2, _col3
Statistics: Num rows: 0 Data size: 0 Basic stats: NONE Column
stats: NONE
File Output Operator
compressed: false
Statistics: Num rows: 0 Data size: 0 Basic stats: NONE Column
stats: NONE
table:
input format: org.apache.hadoop.mapred.TextInputFormat
output format:
org.apache.hadoop.hive.ql.io.HiveIgnoreKeyTextOutputFormat
serde: org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe
Stage: Stage-0
Fetch Operator
limit: -1
Processor Tree:
ListSink
```
@chenghao-intel has a solution in #6413
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