Yadong Qi created SPARK-11580:
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Summary: Just do final aggregation when there is no Exchange
Key: SPARK-11580
URL: https://issues.apache.org/jira/browse/SPARK-11580
Project: Spark
Issue Type: Improvement
Components: SQL
Affects Versions: 1.5.1
Reporter: Yadong Qi
I do the SQL as below:
{code}
cache table src as select * from src distribute by key;
select key, count(value) from src group by key;
{code}
and the Physical Plan is
{code}
TungstenAggregate(key=[key#0],
functions=[(count(value#1),mode=Final,isDistinct=false)],
output=[key#0,_c1#28L])
TungstenAggregate(key=[key#0],
functions=[(count(value#1),mode=Partial,isDistinct=false)],
output=[key#0,currentCount#41L])
InMemoryColumnarTableScan [key#0,value#1], (InMemoryRelation [key#0,value#1],
true, 10000, StorageLevel(true, true, false, true, 1), (TungstenExchange
hashpartitioning(key#0)), Some(src))
{code}
I think if there is no Exchange, just do final aggregation is better, like:
{code}
TungstenAggregate(key=[key#0],
functions=[(count(value#1),mode=Final,isDistinct=false)],
output=[key#0,_c1#28L])
InMemoryColumnarTableScan [key#0,value#1], (InMemoryRelation [key#0,value#1],
true, 10000, StorageLevel(true, true, false, true, 1), (TungstenExchange
hashpartitioning(key#0)), Some(src))
{code}
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