QiangCai opened a new pull request #3681: [CARBONDATA-3752] Reuse Exchange to fix performance issue
URL:
https://github.com/apache/carbondata/pull/3681
### Why is this PR needed?
Spark ReusedExchange rule can't recognition the same Exchange plan on carbon table.
So the query on the carbon table doesn't reuse Exchange, it leads to bad performance.
For Example:
```
create table t1(c1 int, c2 string) using carbondata
explain
select c2, sum(c1) from t1 group by c2
union all
select c2, sum(c1) from t1 group by c2
```
physical plan as following:
```
Union
:- *(2) HashAggregate(keys=[c2#37], functions=[sum(cast(c1#36 as bigint))])
: +- Exchange hashpartitioning(c2#37, 200)
: +- *(1) HashAggregate(keys=[c2#37], functions=[partial_sum(cast(c1#36 as bigint))])
: +- *(1) FileScan carbondata default.t1[c1#36,c2#37] ReadSchema: struct<c1:int,c2:string>
+- *(4) HashAggregate(keys=[c2#37], functions=[sum(cast(c1#36 as bigint))])
+- Exchange hashpartitioning(c2#37, 200)
+- *(3) HashAggregate(keys=[c2#37], functions=[partial_sum(cast(c1#36 as bigint))])
+- *(3) FileScan carbondata default.t1[c1#36,c2#37] ReadSchema: struct<c1:int,c2:string>
```
after change, physical plan as following:
```
Union
:- *(2) HashAggregate(keys=[c2#37], functions=[sum(cast(c1#36 as bigint))])
: +- Exchange hashpartitioning(c2#37, 200)
: +- *(1) HashAggregate(keys=[c2#37], functions=[partial_sum(cast(c1#36 as bigint))])
: +- *(1) FileScan carbondata default.t1[c1#36,c2#37] ReadSchema: struct<c1:int,c2:string>
+- *(4) HashAggregate(keys=[c2#37], functions=[sum(cast(c1#36 as bigint))])
+- ReusedExchange [c2#37, sum#54L], Exchange hashpartitioning(c2#37, 200)
```
### What changes were proposed in this PR?
change CarbonFileIndex class to case class.
### Does this PR introduce any user interface change?
- No
### Is any new testcase added?
- Yes
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