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Posted to common-dev@hadoop.apache.org by "Devaraj Das (JIRA)" <ji...@apache.org> on 2008/03/29 13:24:46 UTC
[jira] Issue Comment Edited: (HADOOP-3130) Shuffling takes too long
to get the last map output.
[ 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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