hive-issues mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Yongzhi Chen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-11502) Map side aggregation is extremely slow
Date Mon, 10 Aug 2015 21:16:45 GMT

    [ https://issues.apache.org/jira/browse/HIVE-11502?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14680783#comment-14680783
] 

Yongzhi Chen commented on HIVE-11502:
-------------------------------------

[~gopalv], I have confirmed that HIVE-7041 caused the regression. Because the hadoop bug is
there for a long time, after hive switch to use hadoop's hashcode, we got hadoop's bug. Thanks
for find the root cause by pointing the hadoop bug.

After I add code in serde/src/java/org/apache/hadoop/hive/serde2/io/DoubleWritable.java
{noformat}
   @Override
   public int hashCode() {
     long v = Double.doubleToLongBits(super.get());
     return (int) (v ^ (v >>> 32));
   }
{noformat}
The group by query can finish in 15 seconds. 

So next step is, how do we fix the issue now? 


> 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) and it is in
type double, 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)

Mime
View raw message