Yongzhi Chen created HIVE-11502:
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Summary: Map side aggregation is extremely slow
Key: HIVE-11502
URL: https://issues.apache.org/jira/browse/HIVE-11502
Project: Hive
Issue Type: Bug
Components: Logical Optimizer, Physical Optimizer
Affects Versions: 1.2.0
Reporter: Yongzhi Chen
Assignee: Yongzhi Chen
For the query as following:
{noformat}
create table tbl2 as
select col1, max(col2) as col2
from tbl1 group by col1;
{noformat}
If the column for group by has many different values (for example 400000), the
map side aggregation is very slow. I ran the query which took more than 3 hours
, after 3 hours, I have to kill the query.
The same query can finish in 7 seconds, if I turn off map side aggregation by:
{noformat}
set hive.map.aggr = false;
{noformat}
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