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From "Eli Collins (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-3768) MR-2450 introduced a significant performance regression
Date Tue, 31 Jan 2012 21:57:59 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-3768?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13197303#comment-13197303

Eli Collins commented on MAPREDUCE-3768:

I don't. This is a pretty straightforward query and it runs 7x faster on MR1 and the same
MR2 build w/o MR-2450 so I suspect MR-2450 had an unintended side-effect, making a thousand
jobs faster doesn't imply it didn't introduce a new bug.
> MR-2450 introduced a significant performance regression
> -------------------------------------------------------
>                 Key: MAPREDUCE-3768
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-3768
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: mrv2
>    Affects Versions: 0.23.1
>            Reporter: Eli Collins
>            Priority: Blocker
> MAPREDUCE-2450 introduced, or at least triggers, a significant performance regression
in Hive. With MR-2450 the execution time of TestCliDriver.skewjoin goes from 2 minutes to
15 minutes. Reverting this change from the build fixes the issue.
> Here's the relevant query:
> {noformat}
> FROM src src1 JOIN src src2 ON (src1.key = src2.key)
> INSERT OVERWRITE TABLE dest_j1 SELECT src1.key, src2.value; 
> {noformat}
> You can reproduce this by running the following from Hive 8.0 against Hadoop built from
> {noformat}
> ant very-clean package test -Dtestcase=TestCliDriver -Dqfile=skewjoin.q
> {noformat}

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