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Date: Tue, 17 Feb 2009 21:02:02 -0800 (PST)
From: "Andy Pavlo (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Updated: (HADOOP-5241) Reduce tasks get stuck because of
 over-estimated task size (regression from 0.18)
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     [ https://issues.apache.org/jira/browse/HADOOP-5241?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Andy Pavlo updated HADOOP-5241:
-------------------------------

    Attachment: hadoop-patched-jobtracker.log.gz

JobTracker logfile running same benchmarks as before without any errors.

> Reduce tasks get stuck because of over-estimated task size (regression from 0.18)
> ---------------------------------------------------------------------------------
>
>                 Key: HADOOP-5241
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5241
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: mapred
>    Affects Versions: 0.19.0
>         Environment: Red Hat Enterprise Linux Server release 5.2
> JDK 1.6.0_11
> Hadoop 0.19.0
>            Reporter: Andy Pavlo
>            Assignee: Sharad Agarwal
>            Priority: Blocker
>             Fix For: 0.19.1
>
>         Attachments: 5241_v1.patch, hadoop-jobtracker.log.gz, hadoop-patched-jobtracker.log.gz, hadoop_task_screenshot.png
>
>
> I have a simple MR benchmark job that computes PageRank on about 600 GB of HTML files using a 100 node cluster. For some reason, my reduce tasks get caught in a pending state. The JobTracker's log gets filled with the following messages:
> 2009-02-12 15:47:29,839 WARN org.apache.hadoop.mapred.JobInProgress: No room for reduce task. Node tracker_d-59.cs.wisc.edu:localhost/127.0.0.1:33227 has 110125027328 bytes free; but we expect reduce input to take 399642198235
> 2009-02-12 15:47:29,852 WARN org.apache.hadoop.mapred.JobInProgress: No room for reduce task. Node tracker_d-67.cs.wisc.edu:localhost/127.0.0.1:48626 has 107537776640 bytes free; but we expect reduce input to take 399642198235
> 2009-02-12 15:47:29,885 WARN org.apache.hadoop.mapred.JobInProgress: No room for reduce task. Node tracker_d-73.cs.wisc.edu:localhost/127.0.0.1:58849 has 113631690752 bytes free; but we expect reduce input to take 399642198235
> <SNIP>
> The weird thing is that I get through about 70 reduce tasks completing before it hangs. If I reduce the amount of the input data on 100 nodes down to 200GB, then it seems to work. As I scale the amount of input to the number of nodes, I can get it work some of the times on 50 nodes and without any problems on 25 nodes and less.
> Note that it worked without any problems on Hadoop 0.18 late last year without changing any of the input data or the actual MR code.

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