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From "Devaraj Das (JIRA)" <j...@apache.org>
Subject [jira] Issue Comment Edited: (HADOOP-3130) Shuffling takes too long to get the last map output.
Date Sat, 29 Mar 2008 12:24:46 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3130?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12583316#action_12583316
] 

devaraj edited comment on HADOOP-3130 at 3/29/08 5:24 AM:
--------------------------------------------------------------

Runping, from the logs it is clear that the backoff strategy hasn't kicked in. I see the following
lines repeating over and over again:
{noformat}
2008-03-29 00:24:16,243 INFO org.apache.hadoop.mapred.ReduceTask: task_200803282211_0482_r_000143_0
Need 1 map output(s)
2008-03-29 00:24:16,245 INFO org.apache.hadoop.mapred.ReduceTask: task_200803282211_0482_r_000143_0:
Got 0 new map-outputs & 0 obsolete map-outputs from tasktracker and 0 map-outputs from
previous failures
2008-03-29 00:24:16,245 INFO org.apache.hadoop.mapred.ReduceTask: task_200803282211_0482_r_000143_0
Got 0 known map output location(s); scheduling...
2008-03-29 00:24:16,245 INFO org.apache.hadoop.mapred.ReduceTask: task_200803282211_0482_r_000143_0
Scheduled 0 of 0 known outputs (0 slow hosts and 0 dup hosts)
{noformat}
This looks like the reducer isn't getting the event for one map from its host tasktracker.
If it had backed off, you would have seen non-zero "slow hosts". 

Did the reducer finally succeed in getting the map output? Which version of hadoop are you
on?

      was (Author: devaraj):
    Runping, from the logs it is clear that the backoff strategy hasn't kicked in. I see the
following lines repeating over and over again:
<noformat>
2008-03-29 00:24:16,243 INFO org.apache.hadoop.mapred.ReduceTask: task_200803282211_0482_r_000143_0
Need 1 map output(s)
2008-03-29 00:24:16,245 INFO org.apache.hadoop.mapred.ReduceTask: task_200803282211_0482_r_000143_0:
Got 0 new map-outputs & 0 obsolete map-outputs from tasktracker and 0 map-outputs from
previous failures
2008-03-29 00:24:16,245 INFO org.apache.hadoop.mapred.ReduceTask: task_200803282211_0482_r_000143_0
Got 0 known map output location(s); scheduling...
2008-03-29 00:24:16,245 INFO org.apache.hadoop.mapred.ReduceTask: task_200803282211_0482_r_000143_0
Scheduled 0 of 0 known outputs (0 slow hosts and 0 dup hosts)
</noformat>
This looks like the reducer isn't getting the event for one map from its host tasktracker.
If it had backed off, you would have seen non-zero "slow hosts". 

Did the reducer finally succeed in getting the map output? Which version of hadoop are you
on?
  
> Shuffling takes too long to get the last map output.
> ----------------------------------------------------
>
>                 Key: HADOOP-3130
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3130
>             Project: Hadoop Core
>          Issue Type: Bug
>            Reporter: Runping Qi
>         Attachments: shuffling.log
>
>
> I noticed that towards the end of shufflling, the map output fetcher of the reducer backs
off too aggressively.
> I attach a fraction of one reduce log of my job.
> Noticed that the last map output was not fetched in 2 minutes.

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