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https://issues.apache.org/jira/browse/MAPREDUCE-3768?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13196723#comment-13196723
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Arun C Murthy commented on MAPREDUCE-3768:
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Eli - Do we know why Hive behaves this way? We've seen significant gains, with
literally thousands of jobs, with MAPREDUCE-2450. Maybe something odd with Hive?
> 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 branch-23.
> {noformat}
> ant very-clean package test -Dtestcase=TestCliDriver -Dqfile=skewjoin.q
> {noformat}
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