[jira] [Created] (HIVE-11502) Map side aggregation is extremely slow

["Yongzhi Chen (JIRA)" <ji...@apache.org>]

Yongzhi Chen created HIVE-11502:
-----------------------------------

             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}




--
This message was sent by Atlassian JIRA
(v6.3.4#6332)