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From "Vinod K V (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-5241) Reduce tasks get stuck because of over-estimated task size (regression from 0.18)
Date Fri, 13 Feb 2009 04:25:59 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-5241?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12673139#action_12673139
] 

Vinod K V commented on HADOOP-5241:
-----------------------------------

Hm.. there does seem to be a bug in the estimation as Jothi pointed out quite some time back
here (https://issues.apache.org/jira/browse/HADOOP-657?focusedCommentId=12622464#action_12622464).
The estimate calculated in that case was ~1000GB!!

Logs would definitely help track this one down.

> 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
>            Priority: Blocker
>
> 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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